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Linux/mm/filemap.c

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  1 /*
  2  *      linux/mm/filemap.c
  3  *
  4  * Copyright (C) 1994-1999  Linus Torvalds
  5  */
  6 
  7 /*
  8  * This file handles the generic file mmap semantics used by
  9  * most "normal" filesystems (but you don't /have/ to use this:
 10  * the NFS filesystem used to do this differently, for example)
 11  */
 12 #include <linux/export.h>
 13 #include <linux/compiler.h>
 14 #include <linux/dax.h>
 15 #include <linux/fs.h>
 16 #include <linux/sched/signal.h>
 17 #include <linux/uaccess.h>
 18 #include <linux/capability.h>
 19 #include <linux/kernel_stat.h>
 20 #include <linux/gfp.h>
 21 #include <linux/mm.h>
 22 #include <linux/swap.h>
 23 #include <linux/mman.h>
 24 #include <linux/pagemap.h>
 25 #include <linux/file.h>
 26 #include <linux/uio.h>
 27 #include <linux/hash.h>
 28 #include <linux/writeback.h>
 29 #include <linux/backing-dev.h>
 30 #include <linux/pagevec.h>
 31 #include <linux/blkdev.h>
 32 #include <linux/security.h>
 33 #include <linux/cpuset.h>
 34 #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
 35 #include <linux/hugetlb.h>
 36 #include <linux/memcontrol.h>
 37 #include <linux/cleancache.h>
 38 #include <linux/shmem_fs.h>
 39 #include <linux/rmap.h>
 40 #include "internal.h"
 41 
 42 #define CREATE_TRACE_POINTS
 43 #include <trace/events/filemap.h>
 44 
 45 /*
 46  * FIXME: remove all knowledge of the buffer layer from the core VM
 47  */
 48 #include <linux/buffer_head.h> /* for try_to_free_buffers */
 49 
 50 #include <asm/mman.h>
 51 
 52 /*
 53  * Shared mappings implemented 30.11.1994. It's not fully working yet,
 54  * though.
 55  *
 56  * Shared mappings now work. 15.8.1995  Bruno.
 57  *
 58  * finished 'unifying' the page and buffer cache and SMP-threaded the
 59  * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
 60  *
 61  * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
 62  */
 63 
 64 /*
 65  * Lock ordering:
 66  *
 67  *  ->i_mmap_rwsem              (truncate_pagecache)
 68  *    ->private_lock            (__free_pte->__set_page_dirty_buffers)
 69  *      ->swap_lock             (exclusive_swap_page, others)
 70  *        ->mapping->tree_lock
 71  *
 72  *  ->i_mutex
 73  *    ->i_mmap_rwsem            (truncate->unmap_mapping_range)
 74  *
 75  *  ->mmap_sem
 76  *    ->i_mmap_rwsem
 77  *      ->page_table_lock or pte_lock   (various, mainly in memory.c)
 78  *        ->mapping->tree_lock  (arch-dependent flush_dcache_mmap_lock)
 79  *
 80  *  ->mmap_sem
 81  *    ->lock_page               (access_process_vm)
 82  *
 83  *  ->i_mutex                   (generic_perform_write)
 84  *    ->mmap_sem                (fault_in_pages_readable->do_page_fault)
 85  *
 86  *  bdi->wb.list_lock
 87  *    sb_lock                   (fs/fs-writeback.c)
 88  *    ->mapping->tree_lock      (__sync_single_inode)
 89  *
 90  *  ->i_mmap_rwsem
 91  *    ->anon_vma.lock           (vma_adjust)
 92  *
 93  *  ->anon_vma.lock
 94  *    ->page_table_lock or pte_lock     (anon_vma_prepare and various)
 95  *
 96  *  ->page_table_lock or pte_lock
 97  *    ->swap_lock               (try_to_unmap_one)
 98  *    ->private_lock            (try_to_unmap_one)
 99  *    ->tree_lock               (try_to_unmap_one)
100  *    ->zone_lru_lock(zone)     (follow_page->mark_page_accessed)
101  *    ->zone_lru_lock(zone)     (check_pte_range->isolate_lru_page)
102  *    ->private_lock            (page_remove_rmap->set_page_dirty)
103  *    ->tree_lock               (page_remove_rmap->set_page_dirty)
104  *    bdi.wb->list_lock         (page_remove_rmap->set_page_dirty)
105  *    ->inode->i_lock           (page_remove_rmap->set_page_dirty)
106  *    ->memcg->move_lock        (page_remove_rmap->lock_page_memcg)
107  *    bdi.wb->list_lock         (zap_pte_range->set_page_dirty)
108  *    ->inode->i_lock           (zap_pte_range->set_page_dirty)
109  *    ->private_lock            (zap_pte_range->__set_page_dirty_buffers)
110  *
111  * ->i_mmap_rwsem
112  *   ->tasklist_lock            (memory_failure, collect_procs_ao)
113  */
114 
115 static int page_cache_tree_insert(struct address_space *mapping,
116                                   struct page *page, void **shadowp)
117 {
118         struct radix_tree_node *node;
119         void **slot;
120         int error;
121 
122         error = __radix_tree_create(&mapping->page_tree, page->index, 0,
123                                     &node, &slot);
124         if (error)
125                 return error;
126         if (*slot) {
127                 void *p;
128 
129                 p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
130                 if (!radix_tree_exceptional_entry(p))
131                         return -EEXIST;
132 
133                 mapping->nrexceptional--;
134                 if (shadowp)
135                         *shadowp = p;
136         }
137         __radix_tree_replace(&mapping->page_tree, node, slot, page,
138                              workingset_lookup_update(mapping));
139         mapping->nrpages++;
140         return 0;
141 }
142 
143 static void page_cache_tree_delete(struct address_space *mapping,
144                                    struct page *page, void *shadow)
145 {
146         int i, nr;
147 
148         /* hugetlb pages are represented by one entry in the radix tree */
149         nr = PageHuge(page) ? 1 : hpage_nr_pages(page);
150 
151         VM_BUG_ON_PAGE(!PageLocked(page), page);
152         VM_BUG_ON_PAGE(PageTail(page), page);
153         VM_BUG_ON_PAGE(nr != 1 && shadow, page);
154 
155         for (i = 0; i < nr; i++) {
156                 struct radix_tree_node *node;
157                 void **slot;
158 
159                 __radix_tree_lookup(&mapping->page_tree, page->index + i,
160                                     &node, &slot);
161 
162                 VM_BUG_ON_PAGE(!node && nr != 1, page);
163 
164                 radix_tree_clear_tags(&mapping->page_tree, node, slot);
165                 __radix_tree_replace(&mapping->page_tree, node, slot, shadow,
166                                 workingset_lookup_update(mapping));
167         }
168 
169         page->mapping = NULL;
170         /* Leave page->index set: truncation lookup relies upon it */
171 
172         if (shadow) {
173                 mapping->nrexceptional += nr;
174                 /*
175                  * Make sure the nrexceptional update is committed before
176                  * the nrpages update so that final truncate racing
177                  * with reclaim does not see both counters 0 at the
178                  * same time and miss a shadow entry.
179                  */
180                 smp_wmb();
181         }
182         mapping->nrpages -= nr;
183 }
184 
185 static void unaccount_page_cache_page(struct address_space *mapping,
186                                       struct page *page)
187 {
188         int nr;
189 
190         /*
191          * if we're uptodate, flush out into the cleancache, otherwise
192          * invalidate any existing cleancache entries.  We can't leave
193          * stale data around in the cleancache once our page is gone
194          */
195         if (PageUptodate(page) && PageMappedToDisk(page))
196                 cleancache_put_page(page);
197         else
198                 cleancache_invalidate_page(mapping, page);
199 
200         VM_BUG_ON_PAGE(PageTail(page), page);
201         VM_BUG_ON_PAGE(page_mapped(page), page);
202         if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(page_mapped(page))) {
203                 int mapcount;
204 
205                 pr_alert("BUG: Bad page cache in process %s  pfn:%05lx\n",
206                          current->comm, page_to_pfn(page));
207                 dump_page(page, "still mapped when deleted");
208                 dump_stack();
209                 add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
210 
211                 mapcount = page_mapcount(page);
212                 if (mapping_exiting(mapping) &&
213                     page_count(page) >= mapcount + 2) {
214                         /*
215                          * All vmas have already been torn down, so it's
216                          * a good bet that actually the page is unmapped,
217                          * and we'd prefer not to leak it: if we're wrong,
218                          * some other bad page check should catch it later.
219                          */
220                         page_mapcount_reset(page);
221                         page_ref_sub(page, mapcount);
222                 }
223         }
224 
225         /* hugetlb pages do not participate in page cache accounting. */
226         if (PageHuge(page))
227                 return;
228 
229         nr = hpage_nr_pages(page);
230 
231         __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
232         if (PageSwapBacked(page)) {
233                 __mod_node_page_state(page_pgdat(page), NR_SHMEM, -nr);
234                 if (PageTransHuge(page))
235                         __dec_node_page_state(page, NR_SHMEM_THPS);
236         } else {
237                 VM_BUG_ON_PAGE(PageTransHuge(page), page);
238         }
239 
240         /*
241          * At this point page must be either written or cleaned by
242          * truncate.  Dirty page here signals a bug and loss of
243          * unwritten data.
244          *
245          * This fixes dirty accounting after removing the page entirely
246          * but leaves PageDirty set: it has no effect for truncated
247          * page and anyway will be cleared before returning page into
248          * buddy allocator.
249          */
250         if (WARN_ON_ONCE(PageDirty(page)))
251                 account_page_cleaned(page, mapping, inode_to_wb(mapping->host));
252 }
253 
254 /*
255  * Delete a page from the page cache and free it. Caller has to make
256  * sure the page is locked and that nobody else uses it - or that usage
257  * is safe.  The caller must hold the mapping's tree_lock.
258  */
259 void __delete_from_page_cache(struct page *page, void *shadow)
260 {
261         struct address_space *mapping = page->mapping;
262 
263         trace_mm_filemap_delete_from_page_cache(page);
264 
265         unaccount_page_cache_page(mapping, page);
266         page_cache_tree_delete(mapping, page, shadow);
267 }
268 
269 static void page_cache_free_page(struct address_space *mapping,
270                                 struct page *page)
271 {
272         void (*freepage)(struct page *);
273 
274         freepage = mapping->a_ops->freepage;
275         if (freepage)
276                 freepage(page);
277 
278         if (PageTransHuge(page) && !PageHuge(page)) {
279                 page_ref_sub(page, HPAGE_PMD_NR);
280                 VM_BUG_ON_PAGE(page_count(page) <= 0, page);
281         } else {
282                 put_page(page);
283         }
284 }
285 
286 /**
287  * delete_from_page_cache - delete page from page cache
288  * @page: the page which the kernel is trying to remove from page cache
289  *
290  * This must be called only on pages that have been verified to be in the page
291  * cache and locked.  It will never put the page into the free list, the caller
292  * has a reference on the page.
293  */
294 void delete_from_page_cache(struct page *page)
295 {
296         struct address_space *mapping = page_mapping(page);
297         unsigned long flags;
298 
299         BUG_ON(!PageLocked(page));
300         spin_lock_irqsave(&mapping->tree_lock, flags);
301         __delete_from_page_cache(page, NULL);
302         spin_unlock_irqrestore(&mapping->tree_lock, flags);
303 
304         page_cache_free_page(mapping, page);
305 }
306 EXPORT_SYMBOL(delete_from_page_cache);
307 
308 /*
309  * page_cache_tree_delete_batch - delete several pages from page cache
310  * @mapping: the mapping to which pages belong
311  * @pvec: pagevec with pages to delete
312  *
313  * The function walks over mapping->page_tree and removes pages passed in @pvec
314  * from the radix tree. The function expects @pvec to be sorted by page index.
315  * It tolerates holes in @pvec (radix tree entries at those indices are not
316  * modified). The function expects only THP head pages to be present in the
317  * @pvec and takes care to delete all corresponding tail pages from the radix
318  * tree as well.
319  *
320  * The function expects mapping->tree_lock to be held.
321  */
322 static void
323 page_cache_tree_delete_batch(struct address_space *mapping,
324                              struct pagevec *pvec)
325 {
326         struct radix_tree_iter iter;
327         void **slot;
328         int total_pages = 0;
329         int i = 0, tail_pages = 0;
330         struct page *page;
331         pgoff_t start;
332 
333         start = pvec->pages[0]->index;
334         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
335                 if (i >= pagevec_count(pvec) && !tail_pages)
336                         break;
337                 page = radix_tree_deref_slot_protected(slot,
338                                                        &mapping->tree_lock);
339                 if (radix_tree_exceptional_entry(page))
340                         continue;
341                 if (!tail_pages) {
342                         /*
343                          * Some page got inserted in our range? Skip it. We
344                          * have our pages locked so they are protected from
345                          * being removed.
346                          */
347                         if (page != pvec->pages[i])
348                                 continue;
349                         WARN_ON_ONCE(!PageLocked(page));
350                         if (PageTransHuge(page) && !PageHuge(page))
351                                 tail_pages = HPAGE_PMD_NR - 1;
352                         page->mapping = NULL;
353                         /*
354                          * Leave page->index set: truncation lookup relies
355                          * upon it
356                          */
357                         i++;
358                 } else {
359                         tail_pages--;
360                 }
361                 radix_tree_clear_tags(&mapping->page_tree, iter.node, slot);
362                 __radix_tree_replace(&mapping->page_tree, iter.node, slot, NULL,
363                                 workingset_lookup_update(mapping));
364                 total_pages++;
365         }
366         mapping->nrpages -= total_pages;
367 }
368 
369 void delete_from_page_cache_batch(struct address_space *mapping,
370                                   struct pagevec *pvec)
371 {
372         int i;
373         unsigned long flags;
374 
375         if (!pagevec_count(pvec))
376                 return;
377 
378         spin_lock_irqsave(&mapping->tree_lock, flags);
379         for (i = 0; i < pagevec_count(pvec); i++) {
380                 trace_mm_filemap_delete_from_page_cache(pvec->pages[i]);
381 
382                 unaccount_page_cache_page(mapping, pvec->pages[i]);
383         }
384         page_cache_tree_delete_batch(mapping, pvec);
385         spin_unlock_irqrestore(&mapping->tree_lock, flags);
386 
387         for (i = 0; i < pagevec_count(pvec); i++)
388                 page_cache_free_page(mapping, pvec->pages[i]);
389 }
390 
391 int filemap_check_errors(struct address_space *mapping)
392 {
393         int ret = 0;
394         /* Check for outstanding write errors */
395         if (test_bit(AS_ENOSPC, &mapping->flags) &&
396             test_and_clear_bit(AS_ENOSPC, &mapping->flags))
397                 ret = -ENOSPC;
398         if (test_bit(AS_EIO, &mapping->flags) &&
399             test_and_clear_bit(AS_EIO, &mapping->flags))
400                 ret = -EIO;
401         return ret;
402 }
403 EXPORT_SYMBOL(filemap_check_errors);
404 
405 static int filemap_check_and_keep_errors(struct address_space *mapping)
406 {
407         /* Check for outstanding write errors */
408         if (test_bit(AS_EIO, &mapping->flags))
409                 return -EIO;
410         if (test_bit(AS_ENOSPC, &mapping->flags))
411                 return -ENOSPC;
412         return 0;
413 }
414 
415 /**
416  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
417  * @mapping:    address space structure to write
418  * @start:      offset in bytes where the range starts
419  * @end:        offset in bytes where the range ends (inclusive)
420  * @sync_mode:  enable synchronous operation
421  *
422  * Start writeback against all of a mapping's dirty pages that lie
423  * within the byte offsets <start, end> inclusive.
424  *
425  * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
426  * opposed to a regular memory cleansing writeback.  The difference between
427  * these two operations is that if a dirty page/buffer is encountered, it must
428  * be waited upon, and not just skipped over.
429  */
430 int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
431                                 loff_t end, int sync_mode)
432 {
433         int ret;
434         struct writeback_control wbc = {
435                 .sync_mode = sync_mode,
436                 .nr_to_write = LONG_MAX,
437                 .range_start = start,
438                 .range_end = end,
439         };
440 
441         if (!mapping_cap_writeback_dirty(mapping))
442                 return 0;
443 
444         wbc_attach_fdatawrite_inode(&wbc, mapping->host);
445         ret = do_writepages(mapping, &wbc);
446         wbc_detach_inode(&wbc);
447         return ret;
448 }
449 
450 static inline int __filemap_fdatawrite(struct address_space *mapping,
451         int sync_mode)
452 {
453         return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
454 }
455 
456 int filemap_fdatawrite(struct address_space *mapping)
457 {
458         return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
459 }
460 EXPORT_SYMBOL(filemap_fdatawrite);
461 
462 int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
463                                 loff_t end)
464 {
465         return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
466 }
467 EXPORT_SYMBOL(filemap_fdatawrite_range);
468 
469 /**
470  * filemap_flush - mostly a non-blocking flush
471  * @mapping:    target address_space
472  *
473  * This is a mostly non-blocking flush.  Not suitable for data-integrity
474  * purposes - I/O may not be started against all dirty pages.
475  */
476 int filemap_flush(struct address_space *mapping)
477 {
478         return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
479 }
480 EXPORT_SYMBOL(filemap_flush);
481 
482 /**
483  * filemap_range_has_page - check if a page exists in range.
484  * @mapping:           address space within which to check
485  * @start_byte:        offset in bytes where the range starts
486  * @end_byte:          offset in bytes where the range ends (inclusive)
487  *
488  * Find at least one page in the range supplied, usually used to check if
489  * direct writing in this range will trigger a writeback.
490  */
491 bool filemap_range_has_page(struct address_space *mapping,
492                            loff_t start_byte, loff_t end_byte)
493 {
494         pgoff_t index = start_byte >> PAGE_SHIFT;
495         pgoff_t end = end_byte >> PAGE_SHIFT;
496         struct page *page;
497 
498         if (end_byte < start_byte)
499                 return false;
500 
501         if (mapping->nrpages == 0)
502                 return false;
503 
504         if (!find_get_pages_range(mapping, &index, end, 1, &page))
505                 return false;
506         put_page(page);
507         return true;
508 }
509 EXPORT_SYMBOL(filemap_range_has_page);
510 
511 static void __filemap_fdatawait_range(struct address_space *mapping,
512                                      loff_t start_byte, loff_t end_byte)
513 {
514         pgoff_t index = start_byte >> PAGE_SHIFT;
515         pgoff_t end = end_byte >> PAGE_SHIFT;
516         struct pagevec pvec;
517         int nr_pages;
518 
519         if (end_byte < start_byte)
520                 return;
521 
522         pagevec_init(&pvec);
523         while (index <= end) {
524                 unsigned i;
525 
526                 nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index,
527                                 end, PAGECACHE_TAG_WRITEBACK);
528                 if (!nr_pages)
529                         break;
530 
531                 for (i = 0; i < nr_pages; i++) {
532                         struct page *page = pvec.pages[i];
533 
534                         wait_on_page_writeback(page);
535                         ClearPageError(page);
536                 }
537                 pagevec_release(&pvec);
538                 cond_resched();
539         }
540 }
541 
542 /**
543  * filemap_fdatawait_range - wait for writeback to complete
544  * @mapping:            address space structure to wait for
545  * @start_byte:         offset in bytes where the range starts
546  * @end_byte:           offset in bytes where the range ends (inclusive)
547  *
548  * Walk the list of under-writeback pages of the given address space
549  * in the given range and wait for all of them.  Check error status of
550  * the address space and return it.
551  *
552  * Since the error status of the address space is cleared by this function,
553  * callers are responsible for checking the return value and handling and/or
554  * reporting the error.
555  */
556 int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
557                             loff_t end_byte)
558 {
559         __filemap_fdatawait_range(mapping, start_byte, end_byte);
560         return filemap_check_errors(mapping);
561 }
562 EXPORT_SYMBOL(filemap_fdatawait_range);
563 
564 /**
565  * file_fdatawait_range - wait for writeback to complete
566  * @file:               file pointing to address space structure to wait for
567  * @start_byte:         offset in bytes where the range starts
568  * @end_byte:           offset in bytes where the range ends (inclusive)
569  *
570  * Walk the list of under-writeback pages of the address space that file
571  * refers to, in the given range and wait for all of them.  Check error
572  * status of the address space vs. the file->f_wb_err cursor and return it.
573  *
574  * Since the error status of the file is advanced by this function,
575  * callers are responsible for checking the return value and handling and/or
576  * reporting the error.
577  */
578 int file_fdatawait_range(struct file *file, loff_t start_byte, loff_t end_byte)
579 {
580         struct address_space *mapping = file->f_mapping;
581 
582         __filemap_fdatawait_range(mapping, start_byte, end_byte);
583         return file_check_and_advance_wb_err(file);
584 }
585 EXPORT_SYMBOL(file_fdatawait_range);
586 
587 /**
588  * filemap_fdatawait_keep_errors - wait for writeback without clearing errors
589  * @mapping: address space structure to wait for
590  *
591  * Walk the list of under-writeback pages of the given address space
592  * and wait for all of them.  Unlike filemap_fdatawait(), this function
593  * does not clear error status of the address space.
594  *
595  * Use this function if callers don't handle errors themselves.  Expected
596  * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
597  * fsfreeze(8)
598  */
599 int filemap_fdatawait_keep_errors(struct address_space *mapping)
600 {
601         __filemap_fdatawait_range(mapping, 0, LLONG_MAX);
602         return filemap_check_and_keep_errors(mapping);
603 }
604 EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
605 
606 static bool mapping_needs_writeback(struct address_space *mapping)
607 {
608         return (!dax_mapping(mapping) && mapping->nrpages) ||
609             (dax_mapping(mapping) && mapping->nrexceptional);
610 }
611 
612 int filemap_write_and_wait(struct address_space *mapping)
613 {
614         int err = 0;
615 
616         if (mapping_needs_writeback(mapping)) {
617                 err = filemap_fdatawrite(mapping);
618                 /*
619                  * Even if the above returned error, the pages may be
620                  * written partially (e.g. -ENOSPC), so we wait for it.
621                  * But the -EIO is special case, it may indicate the worst
622                  * thing (e.g. bug) happened, so we avoid waiting for it.
623                  */
624                 if (err != -EIO) {
625                         int err2 = filemap_fdatawait(mapping);
626                         if (!err)
627                                 err = err2;
628                 } else {
629                         /* Clear any previously stored errors */
630                         filemap_check_errors(mapping);
631                 }
632         } else {
633                 err = filemap_check_errors(mapping);
634         }
635         return err;
636 }
637 EXPORT_SYMBOL(filemap_write_and_wait);
638 
639 /**
640  * filemap_write_and_wait_range - write out & wait on a file range
641  * @mapping:    the address_space for the pages
642  * @lstart:     offset in bytes where the range starts
643  * @lend:       offset in bytes where the range ends (inclusive)
644  *
645  * Write out and wait upon file offsets lstart->lend, inclusive.
646  *
647  * Note that @lend is inclusive (describes the last byte to be written) so
648  * that this function can be used to write to the very end-of-file (end = -1).
649  */
650 int filemap_write_and_wait_range(struct address_space *mapping,
651                                  loff_t lstart, loff_t lend)
652 {
653         int err = 0;
654 
655         if (mapping_needs_writeback(mapping)) {
656                 err = __filemap_fdatawrite_range(mapping, lstart, lend,
657                                                  WB_SYNC_ALL);
658                 /* See comment of filemap_write_and_wait() */
659                 if (err != -EIO) {
660                         int err2 = filemap_fdatawait_range(mapping,
661                                                 lstart, lend);
662                         if (!err)
663                                 err = err2;
664                 } else {
665                         /* Clear any previously stored errors */
666                         filemap_check_errors(mapping);
667                 }
668         } else {
669                 err = filemap_check_errors(mapping);
670         }
671         return err;
672 }
673 EXPORT_SYMBOL(filemap_write_and_wait_range);
674 
675 void __filemap_set_wb_err(struct address_space *mapping, int err)
676 {
677         errseq_t eseq = errseq_set(&mapping->wb_err, err);
678 
679         trace_filemap_set_wb_err(mapping, eseq);
680 }
681 EXPORT_SYMBOL(__filemap_set_wb_err);
682 
683 /**
684  * file_check_and_advance_wb_err - report wb error (if any) that was previously
685  *                                 and advance wb_err to current one
686  * @file: struct file on which the error is being reported
687  *
688  * When userland calls fsync (or something like nfsd does the equivalent), we
689  * want to report any writeback errors that occurred since the last fsync (or
690  * since the file was opened if there haven't been any).
691  *
692  * Grab the wb_err from the mapping. If it matches what we have in the file,
693  * then just quickly return 0. The file is all caught up.
694  *
695  * If it doesn't match, then take the mapping value, set the "seen" flag in
696  * it and try to swap it into place. If it works, or another task beat us
697  * to it with the new value, then update the f_wb_err and return the error
698  * portion. The error at this point must be reported via proper channels
699  * (a'la fsync, or NFS COMMIT operation, etc.).
700  *
701  * While we handle mapping->wb_err with atomic operations, the f_wb_err
702  * value is protected by the f_lock since we must ensure that it reflects
703  * the latest value swapped in for this file descriptor.
704  */
705 int file_check_and_advance_wb_err(struct file *file)
706 {
707         int err = 0;
708         errseq_t old = READ_ONCE(file->f_wb_err);
709         struct address_space *mapping = file->f_mapping;
710 
711         /* Locklessly handle the common case where nothing has changed */
712         if (errseq_check(&mapping->wb_err, old)) {
713                 /* Something changed, must use slow path */
714                 spin_lock(&file->f_lock);
715                 old = file->f_wb_err;
716                 err = errseq_check_and_advance(&mapping->wb_err,
717                                                 &file->f_wb_err);
718                 trace_file_check_and_advance_wb_err(file, old);
719                 spin_unlock(&file->f_lock);
720         }
721 
722         /*
723          * We're mostly using this function as a drop in replacement for
724          * filemap_check_errors. Clear AS_EIO/AS_ENOSPC to emulate the effect
725          * that the legacy code would have had on these flags.
726          */
727         clear_bit(AS_EIO, &mapping->flags);
728         clear_bit(AS_ENOSPC, &mapping->flags);
729         return err;
730 }
731 EXPORT_SYMBOL(file_check_and_advance_wb_err);
732 
733 /**
734  * file_write_and_wait_range - write out & wait on a file range
735  * @file:       file pointing to address_space with pages
736  * @lstart:     offset in bytes where the range starts
737  * @lend:       offset in bytes where the range ends (inclusive)
738  *
739  * Write out and wait upon file offsets lstart->lend, inclusive.
740  *
741  * Note that @lend is inclusive (describes the last byte to be written) so
742  * that this function can be used to write to the very end-of-file (end = -1).
743  *
744  * After writing out and waiting on the data, we check and advance the
745  * f_wb_err cursor to the latest value, and return any errors detected there.
746  */
747 int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
748 {
749         int err = 0, err2;
750         struct address_space *mapping = file->f_mapping;
751 
752         if (mapping_needs_writeback(mapping)) {
753                 err = __filemap_fdatawrite_range(mapping, lstart, lend,
754                                                  WB_SYNC_ALL);
755                 /* See comment of filemap_write_and_wait() */
756                 if (err != -EIO)
757                         __filemap_fdatawait_range(mapping, lstart, lend);
758         }
759         err2 = file_check_and_advance_wb_err(file);
760         if (!err)
761                 err = err2;
762         return err;
763 }
764 EXPORT_SYMBOL(file_write_and_wait_range);
765 
766 /**
767  * replace_page_cache_page - replace a pagecache page with a new one
768  * @old:        page to be replaced
769  * @new:        page to replace with
770  * @gfp_mask:   allocation mode
771  *
772  * This function replaces a page in the pagecache with a new one.  On
773  * success it acquires the pagecache reference for the new page and
774  * drops it for the old page.  Both the old and new pages must be
775  * locked.  This function does not add the new page to the LRU, the
776  * caller must do that.
777  *
778  * The remove + add is atomic.  The only way this function can fail is
779  * memory allocation failure.
780  */
781 int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
782 {
783         int error;
784 
785         VM_BUG_ON_PAGE(!PageLocked(old), old);
786         VM_BUG_ON_PAGE(!PageLocked(new), new);
787         VM_BUG_ON_PAGE(new->mapping, new);
788 
789         error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
790         if (!error) {
791                 struct address_space *mapping = old->mapping;
792                 void (*freepage)(struct page *);
793                 unsigned long flags;
794 
795                 pgoff_t offset = old->index;
796                 freepage = mapping->a_ops->freepage;
797 
798                 get_page(new);
799                 new->mapping = mapping;
800                 new->index = offset;
801 
802                 spin_lock_irqsave(&mapping->tree_lock, flags);
803                 __delete_from_page_cache(old, NULL);
804                 error = page_cache_tree_insert(mapping, new, NULL);
805                 BUG_ON(error);
806 
807                 /*
808                  * hugetlb pages do not participate in page cache accounting.
809                  */
810                 if (!PageHuge(new))
811                         __inc_node_page_state(new, NR_FILE_PAGES);
812                 if (PageSwapBacked(new))
813                         __inc_node_page_state(new, NR_SHMEM);
814                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
815                 mem_cgroup_migrate(old, new);
816                 radix_tree_preload_end();
817                 if (freepage)
818                         freepage(old);
819                 put_page(old);
820         }
821 
822         return error;
823 }
824 EXPORT_SYMBOL_GPL(replace_page_cache_page);
825 
826 static int __add_to_page_cache_locked(struct page *page,
827                                       struct address_space *mapping,
828                                       pgoff_t offset, gfp_t gfp_mask,
829                                       void **shadowp)
830 {
831         int huge = PageHuge(page);
832         struct mem_cgroup *memcg;
833         int error;
834 
835         VM_BUG_ON_PAGE(!PageLocked(page), page);
836         VM_BUG_ON_PAGE(PageSwapBacked(page), page);
837 
838         if (!huge) {
839                 error = mem_cgroup_try_charge(page, current->mm,
840                                               gfp_mask, &memcg, false);
841                 if (error)
842                         return error;
843         }
844 
845         error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
846         if (error) {
847                 if (!huge)
848                         mem_cgroup_cancel_charge(page, memcg, false);
849                 return error;
850         }
851 
852         get_page(page);
853         page->mapping = mapping;
854         page->index = offset;
855 
856         spin_lock_irq(&mapping->tree_lock);
857         error = page_cache_tree_insert(mapping, page, shadowp);
858         radix_tree_preload_end();
859         if (unlikely(error))
860                 goto err_insert;
861 
862         /* hugetlb pages do not participate in page cache accounting. */
863         if (!huge)
864                 __inc_node_page_state(page, NR_FILE_PAGES);
865         spin_unlock_irq(&mapping->tree_lock);
866         if (!huge)
867                 mem_cgroup_commit_charge(page, memcg, false, false);
868         trace_mm_filemap_add_to_page_cache(page);
869         return 0;
870 err_insert:
871         page->mapping = NULL;
872         /* Leave page->index set: truncation relies upon it */
873         spin_unlock_irq(&mapping->tree_lock);
874         if (!huge)
875                 mem_cgroup_cancel_charge(page, memcg, false);
876         put_page(page);
877         return error;
878 }
879 
880 /**
881  * add_to_page_cache_locked - add a locked page to the pagecache
882  * @page:       page to add
883  * @mapping:    the page's address_space
884  * @offset:     page index
885  * @gfp_mask:   page allocation mode
886  *
887  * This function is used to add a page to the pagecache. It must be locked.
888  * This function does not add the page to the LRU.  The caller must do that.
889  */
890 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
891                 pgoff_t offset, gfp_t gfp_mask)
892 {
893         return __add_to_page_cache_locked(page, mapping, offset,
894                                           gfp_mask, NULL);
895 }
896 EXPORT_SYMBOL(add_to_page_cache_locked);
897 
898 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
899                                 pgoff_t offset, gfp_t gfp_mask)
900 {
901         void *shadow = NULL;
902         int ret;
903 
904         __SetPageLocked(page);
905         ret = __add_to_page_cache_locked(page, mapping, offset,
906                                          gfp_mask, &shadow);
907         if (unlikely(ret))
908                 __ClearPageLocked(page);
909         else {
910                 /*
911                  * The page might have been evicted from cache only
912                  * recently, in which case it should be activated like
913                  * any other repeatedly accessed page.
914                  * The exception is pages getting rewritten; evicting other
915                  * data from the working set, only to cache data that will
916                  * get overwritten with something else, is a waste of memory.
917                  */
918                 if (!(gfp_mask & __GFP_WRITE) &&
919                     shadow && workingset_refault(shadow)) {
920                         SetPageActive(page);
921                         workingset_activation(page);
922                 } else
923                         ClearPageActive(page);
924                 lru_cache_add(page);
925         }
926         return ret;
927 }
928 EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
929 
930 #ifdef CONFIG_NUMA
931 struct page *__page_cache_alloc(gfp_t gfp)
932 {
933         int n;
934         struct page *page;
935 
936         if (cpuset_do_page_mem_spread()) {
937                 unsigned int cpuset_mems_cookie;
938                 do {
939                         cpuset_mems_cookie = read_mems_allowed_begin();
940                         n = cpuset_mem_spread_node();
941                         page = __alloc_pages_node(n, gfp, 0);
942                 } while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
943 
944                 return page;
945         }
946         return alloc_pages(gfp, 0);
947 }
948 EXPORT_SYMBOL(__page_cache_alloc);
949 #endif
950 
951 /*
952  * In order to wait for pages to become available there must be
953  * waitqueues associated with pages. By using a hash table of
954  * waitqueues where the bucket discipline is to maintain all
955  * waiters on the same queue and wake all when any of the pages
956  * become available, and for the woken contexts to check to be
957  * sure the appropriate page became available, this saves space
958  * at a cost of "thundering herd" phenomena during rare hash
959  * collisions.
960  */
961 #define PAGE_WAIT_TABLE_BITS 8
962 #define PAGE_WAIT_TABLE_SIZE (1 << PAGE_WAIT_TABLE_BITS)
963 static wait_queue_head_t page_wait_table[PAGE_WAIT_TABLE_SIZE] __cacheline_aligned;
964 
965 static wait_queue_head_t *page_waitqueue(struct page *page)
966 {
967         return &page_wait_table[hash_ptr(page, PAGE_WAIT_TABLE_BITS)];
968 }
969 
970 void __init pagecache_init(void)
971 {
972         int i;
973 
974         for (i = 0; i < PAGE_WAIT_TABLE_SIZE; i++)
975                 init_waitqueue_head(&page_wait_table[i]);
976 
977         page_writeback_init();
978 }
979 
980 /* This has the same layout as wait_bit_key - see fs/cachefiles/rdwr.c */
981 struct wait_page_key {
982         struct page *page;
983         int bit_nr;
984         int page_match;
985 };
986 
987 struct wait_page_queue {
988         struct page *page;
989         int bit_nr;
990         wait_queue_entry_t wait;
991 };
992 
993 static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *arg)
994 {
995         struct wait_page_key *key = arg;
996         struct wait_page_queue *wait_page
997                 = container_of(wait, struct wait_page_queue, wait);
998 
999         if (wait_page->page != key->page)
1000                return 0;
1001         key->page_match = 1;
1002 
1003         if (wait_page->bit_nr != key->bit_nr)
1004                 return 0;
1005 
1006         /* Stop walking if it's locked */
1007         if (test_bit(key->bit_nr, &key->page->flags))
1008                 return -1;
1009 
1010         return autoremove_wake_function(wait, mode, sync, key);
1011 }
1012 
1013 static void wake_up_page_bit(struct page *page, int bit_nr)
1014 {
1015         wait_queue_head_t *q = page_waitqueue(page);
1016         struct wait_page_key key;
1017         unsigned long flags;
1018         wait_queue_entry_t bookmark;
1019 
1020         key.page = page;
1021         key.bit_nr = bit_nr;
1022         key.page_match = 0;
1023 
1024         bookmark.flags = 0;
1025         bookmark.private = NULL;
1026         bookmark.func = NULL;
1027         INIT_LIST_HEAD(&bookmark.entry);
1028 
1029         spin_lock_irqsave(&q->lock, flags);
1030         __wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
1031 
1032         while (bookmark.flags & WQ_FLAG_BOOKMARK) {
1033                 /*
1034                  * Take a breather from holding the lock,
1035                  * allow pages that finish wake up asynchronously
1036                  * to acquire the lock and remove themselves
1037                  * from wait queue
1038                  */
1039                 spin_unlock_irqrestore(&q->lock, flags);
1040                 cpu_relax();
1041                 spin_lock_irqsave(&q->lock, flags);
1042                 __wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
1043         }
1044 
1045         /*
1046          * It is possible for other pages to have collided on the waitqueue
1047          * hash, so in that case check for a page match. That prevents a long-
1048          * term waiter
1049          *
1050          * It is still possible to miss a case here, when we woke page waiters
1051          * and removed them from the waitqueue, but there are still other
1052          * page waiters.
1053          */
1054         if (!waitqueue_active(q) || !key.page_match) {
1055                 ClearPageWaiters(page);
1056                 /*
1057                  * It's possible to miss clearing Waiters here, when we woke
1058                  * our page waiters, but the hashed waitqueue has waiters for
1059                  * other pages on it.
1060                  *
1061                  * That's okay, it's a rare case. The next waker will clear it.
1062                  */
1063         }
1064         spin_unlock_irqrestore(&q->lock, flags);
1065 }
1066 
1067 static void wake_up_page(struct page *page, int bit)
1068 {
1069         if (!PageWaiters(page))
1070                 return;
1071         wake_up_page_bit(page, bit);
1072 }
1073 
1074 static inline int wait_on_page_bit_common(wait_queue_head_t *q,
1075                 struct page *page, int bit_nr, int state, bool lock)
1076 {
1077         struct wait_page_queue wait_page;
1078         wait_queue_entry_t *wait = &wait_page.wait;
1079         int ret = 0;
1080 
1081         init_wait(wait);
1082         wait->flags = lock ? WQ_FLAG_EXCLUSIVE : 0;
1083         wait->func = wake_page_function;
1084         wait_page.page = page;
1085         wait_page.bit_nr = bit_nr;
1086 
1087         for (;;) {
1088                 spin_lock_irq(&q->lock);
1089 
1090                 if (likely(list_empty(&wait->entry))) {
1091                         __add_wait_queue_entry_tail(q, wait);
1092                         SetPageWaiters(page);
1093                 }
1094 
1095                 set_current_state(state);
1096 
1097                 spin_unlock_irq(&q->lock);
1098 
1099                 if (likely(test_bit(bit_nr, &page->flags))) {
1100                         io_schedule();
1101                 }
1102 
1103                 if (lock) {
1104                         if (!test_and_set_bit_lock(bit_nr, &page->flags))
1105                                 break;
1106                 } else {
1107                         if (!test_bit(bit_nr, &page->flags))
1108                                 break;
1109                 }
1110 
1111                 if (unlikely(signal_pending_state(state, current))) {
1112                         ret = -EINTR;
1113                         break;
1114                 }
1115         }
1116 
1117         finish_wait(q, wait);
1118 
1119         /*
1120          * A signal could leave PageWaiters set. Clearing it here if
1121          * !waitqueue_active would be possible (by open-coding finish_wait),
1122          * but still fail to catch it in the case of wait hash collision. We
1123          * already can fail to clear wait hash collision cases, so don't
1124          * bother with signals either.
1125          */
1126 
1127         return ret;
1128 }
1129 
1130 void wait_on_page_bit(struct page *page, int bit_nr)
1131 {
1132         wait_queue_head_t *q = page_waitqueue(page);
1133         wait_on_page_bit_common(q, page, bit_nr, TASK_UNINTERRUPTIBLE, false);
1134 }
1135 EXPORT_SYMBOL(wait_on_page_bit);
1136 
1137 int wait_on_page_bit_killable(struct page *page, int bit_nr)
1138 {
1139         wait_queue_head_t *q = page_waitqueue(page);
1140         return wait_on_page_bit_common(q, page, bit_nr, TASK_KILLABLE, false);
1141 }
1142 EXPORT_SYMBOL(wait_on_page_bit_killable);
1143 
1144 /**
1145  * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
1146  * @page: Page defining the wait queue of interest
1147  * @waiter: Waiter to add to the queue
1148  *
1149  * Add an arbitrary @waiter to the wait queue for the nominated @page.
1150  */
1151 void add_page_wait_queue(struct page *page, wait_queue_entry_t *waiter)
1152 {
1153         wait_queue_head_t *q = page_waitqueue(page);
1154         unsigned long flags;
1155 
1156         spin_lock_irqsave(&q->lock, flags);
1157         __add_wait_queue_entry_tail(q, waiter);
1158         SetPageWaiters(page);
1159         spin_unlock_irqrestore(&q->lock, flags);
1160 }
1161 EXPORT_SYMBOL_GPL(add_page_wait_queue);
1162 
1163 #ifndef clear_bit_unlock_is_negative_byte
1164 
1165 /*
1166  * PG_waiters is the high bit in the same byte as PG_lock.
1167  *
1168  * On x86 (and on many other architectures), we can clear PG_lock and
1169  * test the sign bit at the same time. But if the architecture does
1170  * not support that special operation, we just do this all by hand
1171  * instead.
1172  *
1173  * The read of PG_waiters has to be after (or concurrently with) PG_locked
1174  * being cleared, but a memory barrier should be unneccssary since it is
1175  * in the same byte as PG_locked.
1176  */
1177 static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem)
1178 {
1179         clear_bit_unlock(nr, mem);
1180         /* smp_mb__after_atomic(); */
1181         return test_bit(PG_waiters, mem);
1182 }
1183 
1184 #endif
1185 
1186 /**
1187  * unlock_page - unlock a locked page
1188  * @page: the page
1189  *
1190  * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
1191  * Also wakes sleepers in wait_on_page_writeback() because the wakeup
1192  * mechanism between PageLocked pages and PageWriteback pages is shared.
1193  * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
1194  *
1195  * Note that this depends on PG_waiters being the sign bit in the byte
1196  * that contains PG_locked - thus the BUILD_BUG_ON(). That allows us to
1197  * clear the PG_locked bit and test PG_waiters at the same time fairly
1198  * portably (architectures that do LL/SC can test any bit, while x86 can
1199  * test the sign bit).
1200  */
1201 void unlock_page(struct page *page)
1202 {
1203         BUILD_BUG_ON(PG_waiters != 7);
1204         page = compound_head(page);
1205         VM_BUG_ON_PAGE(!PageLocked(page), page);
1206         if (clear_bit_unlock_is_negative_byte(PG_locked, &page->flags))
1207                 wake_up_page_bit(page, PG_locked);
1208 }
1209 EXPORT_SYMBOL(unlock_page);
1210 
1211 /**
1212  * end_page_writeback - end writeback against a page
1213  * @page: the page
1214  */
1215 void end_page_writeback(struct page *page)
1216 {
1217         /*
1218          * TestClearPageReclaim could be used here but it is an atomic
1219          * operation and overkill in this particular case. Failing to
1220          * shuffle a page marked for immediate reclaim is too mild to
1221          * justify taking an atomic operation penalty at the end of
1222          * ever page writeback.
1223          */
1224         if (PageReclaim(page)) {
1225                 ClearPageReclaim(page);
1226                 rotate_reclaimable_page(page);
1227         }
1228 
1229         if (!test_clear_page_writeback(page))
1230                 BUG();
1231 
1232         smp_mb__after_atomic();
1233         wake_up_page(page, PG_writeback);
1234 }
1235 EXPORT_SYMBOL(end_page_writeback);
1236 
1237 /*
1238  * After completing I/O on a page, call this routine to update the page
1239  * flags appropriately
1240  */
1241 void page_endio(struct page *page, bool is_write, int err)
1242 {
1243         if (!is_write) {
1244                 if (!err) {
1245                         SetPageUptodate(page);
1246                 } else {
1247                         ClearPageUptodate(page);
1248                         SetPageError(page);
1249                 }
1250                 unlock_page(page);
1251         } else {
1252                 if (err) {
1253                         struct address_space *mapping;
1254 
1255                         SetPageError(page);
1256                         mapping = page_mapping(page);
1257                         if (mapping)
1258                                 mapping_set_error(mapping, err);
1259                 }
1260                 end_page_writeback(page);
1261         }
1262 }
1263 EXPORT_SYMBOL_GPL(page_endio);
1264 
1265 /**
1266  * __lock_page - get a lock on the page, assuming we need to sleep to get it
1267  * @__page: the page to lock
1268  */
1269 void __lock_page(struct page *__page)
1270 {
1271         struct page *page = compound_head(__page);
1272         wait_queue_head_t *q = page_waitqueue(page);
1273         wait_on_page_bit_common(q, page, PG_locked, TASK_UNINTERRUPTIBLE, true);
1274 }
1275 EXPORT_SYMBOL(__lock_page);
1276 
1277 int __lock_page_killable(struct page *__page)
1278 {
1279         struct page *page = compound_head(__page);
1280         wait_queue_head_t *q = page_waitqueue(page);
1281         return wait_on_page_bit_common(q, page, PG_locked, TASK_KILLABLE, true);
1282 }
1283 EXPORT_SYMBOL_GPL(__lock_page_killable);
1284 
1285 /*
1286  * Return values:
1287  * 1 - page is locked; mmap_sem is still held.
1288  * 0 - page is not locked.
1289  *     mmap_sem has been released (up_read()), unless flags had both
1290  *     FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
1291  *     which case mmap_sem is still held.
1292  *
1293  * If neither ALLOW_RETRY nor KILLABLE are set, will always return 1
1294  * with the page locked and the mmap_sem unperturbed.
1295  */
1296 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
1297                          unsigned int flags)
1298 {
1299         if (flags & FAULT_FLAG_ALLOW_RETRY) {
1300                 /*
1301                  * CAUTION! In this case, mmap_sem is not released
1302                  * even though return 0.
1303                  */
1304                 if (flags & FAULT_FLAG_RETRY_NOWAIT)
1305                         return 0;
1306 
1307                 up_read(&mm->mmap_sem);
1308                 if (flags & FAULT_FLAG_KILLABLE)
1309                         wait_on_page_locked_killable(page);
1310                 else
1311                         wait_on_page_locked(page);
1312                 return 0;
1313         } else {
1314                 if (flags & FAULT_FLAG_KILLABLE) {
1315                         int ret;
1316 
1317                         ret = __lock_page_killable(page);
1318                         if (ret) {
1319                                 up_read(&mm->mmap_sem);
1320                                 return 0;
1321                         }
1322                 } else
1323                         __lock_page(page);
1324                 return 1;
1325         }
1326 }
1327 
1328 /**
1329  * page_cache_next_hole - find the next hole (not-present entry)
1330  * @mapping: mapping
1331  * @index: index
1332  * @max_scan: maximum range to search
1333  *
1334  * Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the
1335  * lowest indexed hole.
1336  *
1337  * Returns: the index of the hole if found, otherwise returns an index
1338  * outside of the set specified (in which case 'return - index >=
1339  * max_scan' will be true). In rare cases of index wrap-around, 0 will
1340  * be returned.
1341  *
1342  * page_cache_next_hole may be called under rcu_read_lock. However,
1343  * like radix_tree_gang_lookup, this will not atomically search a
1344  * snapshot of the tree at a single point in time. For example, if a
1345  * hole is created at index 5, then subsequently a hole is created at
1346  * index 10, page_cache_next_hole covering both indexes may return 10
1347  * if called under rcu_read_lock.
1348  */
1349 pgoff_t page_cache_next_hole(struct address_space *mapping,
1350                              pgoff_t index, unsigned long max_scan)
1351 {
1352         unsigned long i;
1353 
1354         for (i = 0; i < max_scan; i++) {
1355                 struct page *page;
1356 
1357                 page = radix_tree_lookup(&mapping->page_tree, index);
1358                 if (!page || radix_tree_exceptional_entry(page))
1359                         break;
1360                 index++;
1361                 if (index == 0)
1362                         break;
1363         }
1364 
1365         return index;
1366 }
1367 EXPORT_SYMBOL(page_cache_next_hole);
1368 
1369 /**
1370  * page_cache_prev_hole - find the prev hole (not-present entry)
1371  * @mapping: mapping
1372  * @index: index
1373  * @max_scan: maximum range to search
1374  *
1375  * Search backwards in the range [max(index-max_scan+1, 0), index] for
1376  * the first hole.
1377  *
1378  * Returns: the index of the hole if found, otherwise returns an index
1379  * outside of the set specified (in which case 'index - return >=
1380  * max_scan' will be true). In rare cases of wrap-around, ULONG_MAX
1381  * will be returned.
1382  *
1383  * page_cache_prev_hole may be called under rcu_read_lock. However,
1384  * like radix_tree_gang_lookup, this will not atomically search a
1385  * snapshot of the tree at a single point in time. For example, if a
1386  * hole is created at index 10, then subsequently a hole is created at
1387  * index 5, page_cache_prev_hole covering both indexes may return 5 if
1388  * called under rcu_read_lock.
1389  */
1390 pgoff_t page_cache_prev_hole(struct address_space *mapping,
1391                              pgoff_t index, unsigned long max_scan)
1392 {
1393         unsigned long i;
1394 
1395         for (i = 0; i < max_scan; i++) {
1396                 struct page *page;
1397 
1398                 page = radix_tree_lookup(&mapping->page_tree, index);
1399                 if (!page || radix_tree_exceptional_entry(page))
1400                         break;
1401                 index--;
1402                 if (index == ULONG_MAX)
1403                         break;
1404         }
1405 
1406         return index;
1407 }
1408 EXPORT_SYMBOL(page_cache_prev_hole);
1409 
1410 /**
1411  * find_get_entry - find and get a page cache entry
1412  * @mapping: the address_space to search
1413  * @offset: the page cache index
1414  *
1415  * Looks up the page cache slot at @mapping & @offset.  If there is a
1416  * page cache page, it is returned with an increased refcount.
1417  *
1418  * If the slot holds a shadow entry of a previously evicted page, or a
1419  * swap entry from shmem/tmpfs, it is returned.
1420  *
1421  * Otherwise, %NULL is returned.
1422  */
1423 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
1424 {
1425         void **pagep;
1426         struct page *head, *page;
1427 
1428         rcu_read_lock();
1429 repeat:
1430         page = NULL;
1431         pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
1432         if (pagep) {
1433                 page = radix_tree_deref_slot(pagep);
1434                 if (unlikely(!page))
1435                         goto out;
1436                 if (radix_tree_exception(page)) {
1437                         if (radix_tree_deref_retry(page))
1438                                 goto repeat;
1439                         /*
1440                          * A shadow entry of a recently evicted page,
1441                          * or a swap entry from shmem/tmpfs.  Return
1442                          * it without attempting to raise page count.
1443                          */
1444                         goto out;
1445                 }
1446 
1447                 head = compound_head(page);
1448                 if (!page_cache_get_speculative(head))
1449                         goto repeat;
1450 
1451                 /* The page was split under us? */
1452                 if (compound_head(page) != head) {
1453                         put_page(head);
1454                         goto repeat;
1455                 }
1456 
1457                 /*
1458                  * Has the page moved?
1459                  * This is part of the lockless pagecache protocol. See
1460                  * include/linux/pagemap.h for details.
1461                  */
1462                 if (unlikely(page != *pagep)) {
1463                         put_page(head);
1464                         goto repeat;
1465                 }
1466         }
1467 out:
1468         rcu_read_unlock();
1469 
1470         return page;
1471 }
1472 EXPORT_SYMBOL(find_get_entry);
1473 
1474 /**
1475  * find_lock_entry - locate, pin and lock a page cache entry
1476  * @mapping: the address_space to search
1477  * @offset: the page cache index
1478  *
1479  * Looks up the page cache slot at @mapping & @offset.  If there is a
1480  * page cache page, it is returned locked and with an increased
1481  * refcount.
1482  *
1483  * If the slot holds a shadow entry of a previously evicted page, or a
1484  * swap entry from shmem/tmpfs, it is returned.
1485  *
1486  * Otherwise, %NULL is returned.
1487  *
1488  * find_lock_entry() may sleep.
1489  */
1490 struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
1491 {
1492         struct page *page;
1493 
1494 repeat:
1495         page = find_get_entry(mapping, offset);
1496         if (page && !radix_tree_exception(page)) {
1497                 lock_page(page);
1498                 /* Has the page been truncated? */
1499                 if (unlikely(page_mapping(page) != mapping)) {
1500                         unlock_page(page);
1501                         put_page(page);
1502                         goto repeat;
1503                 }
1504                 VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
1505         }
1506         return page;
1507 }
1508 EXPORT_SYMBOL(find_lock_entry);
1509 
1510 /**
1511  * pagecache_get_page - find and get a page reference
1512  * @mapping: the address_space to search
1513  * @offset: the page index
1514  * @fgp_flags: PCG flags
1515  * @gfp_mask: gfp mask to use for the page cache data page allocation
1516  *
1517  * Looks up the page cache slot at @mapping & @offset.
1518  *
1519  * PCG flags modify how the page is returned.
1520  *
1521  * @fgp_flags can be:
1522  *
1523  * - FGP_ACCESSED: the page will be marked accessed
1524  * - FGP_LOCK: Page is return locked
1525  * - FGP_CREAT: If page is not present then a new page is allocated using
1526  *   @gfp_mask and added to the page cache and the VM's LRU
1527  *   list. The page is returned locked and with an increased
1528  *   refcount. Otherwise, NULL is returned.
1529  *
1530  * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
1531  * if the GFP flags specified for FGP_CREAT are atomic.
1532  *
1533  * If there is a page cache page, it is returned with an increased refcount.
1534  */
1535 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
1536         int fgp_flags, gfp_t gfp_mask)
1537 {
1538         struct page *page;
1539 
1540 repeat:
1541         page = find_get_entry(mapping, offset);
1542         if (radix_tree_exceptional_entry(page))
1543                 page = NULL;
1544         if (!page)
1545                 goto no_page;
1546 
1547         if (fgp_flags & FGP_LOCK) {
1548                 if (fgp_flags & FGP_NOWAIT) {
1549                         if (!trylock_page(page)) {
1550                                 put_page(page);
1551                                 return NULL;
1552                         }
1553                 } else {
1554                         lock_page(page);
1555                 }
1556 
1557                 /* Has the page been truncated? */
1558                 if (unlikely(page->mapping != mapping)) {
1559                         unlock_page(page);
1560                         put_page(page);
1561                         goto repeat;
1562                 }
1563                 VM_BUG_ON_PAGE(page->index != offset, page);
1564         }
1565 
1566         if (page && (fgp_flags & FGP_ACCESSED))
1567                 mark_page_accessed(page);
1568 
1569 no_page:
1570         if (!page && (fgp_flags & FGP_CREAT)) {
1571                 int err;
1572                 if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping))
1573                         gfp_mask |= __GFP_WRITE;
1574                 if (fgp_flags & FGP_NOFS)
1575                         gfp_mask &= ~__GFP_FS;
1576 
1577                 page = __page_cache_alloc(gfp_mask);
1578                 if (!page)
1579                         return NULL;
1580 
1581                 if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
1582                         fgp_flags |= FGP_LOCK;
1583 
1584                 /* Init accessed so avoid atomic mark_page_accessed later */
1585                 if (fgp_flags & FGP_ACCESSED)
1586                         __SetPageReferenced(page);
1587 
1588                 err = add_to_page_cache_lru(page, mapping, offset,
1589                                 gfp_mask & GFP_RECLAIM_MASK);
1590                 if (unlikely(err)) {
1591                         put_page(page);
1592                         page = NULL;
1593                         if (err == -EEXIST)
1594                                 goto repeat;
1595                 }
1596         }
1597 
1598         return page;
1599 }
1600 EXPORT_SYMBOL(pagecache_get_page);
1601 
1602 /**
1603  * find_get_entries - gang pagecache lookup
1604  * @mapping:    The address_space to search
1605  * @start:      The starting page cache index
1606  * @nr_entries: The maximum number of entries
1607  * @entries:    Where the resulting entries are placed
1608  * @indices:    The cache indices corresponding to the entries in @entries
1609  *
1610  * find_get_entries() will search for and return a group of up to
1611  * @nr_entries entries in the mapping.  The entries are placed at
1612  * @entries.  find_get_entries() takes a reference against any actual
1613  * pages it returns.
1614  *
1615  * The search returns a group of mapping-contiguous page cache entries
1616  * with ascending indexes.  There may be holes in the indices due to
1617  * not-present pages.
1618  *
1619  * Any shadow entries of evicted pages, or swap entries from
1620  * shmem/tmpfs, are included in the returned array.
1621  *
1622  * find_get_entries() returns the number of pages and shadow entries
1623  * which were found.
1624  */
1625 unsigned find_get_entries(struct address_space *mapping,
1626                           pgoff_t start, unsigned int nr_entries,
1627                           struct page **entries, pgoff_t *indices)
1628 {
1629         void **slot;
1630         unsigned int ret = 0;
1631         struct radix_tree_iter iter;
1632 
1633         if (!nr_entries)
1634                 return 0;
1635 
1636         rcu_read_lock();
1637         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1638                 struct page *head, *page;
1639 repeat:
1640                 page = radix_tree_deref_slot(slot);
1641                 if (unlikely(!page))
1642                         continue;
1643                 if (radix_tree_exception(page)) {
1644                         if (radix_tree_deref_retry(page)) {
1645                                 slot = radix_tree_iter_retry(&iter);
1646                                 continue;
1647                         }
1648                         /*
1649                          * A shadow entry of a recently evicted page, a swap
1650                          * entry from shmem/tmpfs or a DAX entry.  Return it
1651                          * without attempting to raise page count.
1652                          */
1653                         goto export;
1654                 }
1655 
1656                 head = compound_head(page);
1657                 if (!page_cache_get_speculative(head))
1658                         goto repeat;
1659 
1660                 /* The page was split under us? */
1661                 if (compound_head(page) != head) {
1662                         put_page(head);
1663                         goto repeat;
1664                 }
1665 
1666                 /* Has the page moved? */
1667                 if (unlikely(page != *slot)) {
1668                         put_page(head);
1669                         goto repeat;
1670                 }
1671 export:
1672                 indices[ret] = iter.index;
1673                 entries[ret] = page;
1674                 if (++ret == nr_entries)
1675                         break;
1676         }
1677         rcu_read_unlock();
1678         return ret;
1679 }
1680 
1681 /**
1682  * find_get_pages_range - gang pagecache lookup
1683  * @mapping:    The address_space to search
1684  * @start:      The starting page index
1685  * @end:        The final page index (inclusive)
1686  * @nr_pages:   The maximum number of pages
1687  * @pages:      Where the resulting pages are placed
1688  *
1689  * find_get_pages_range() will search for and return a group of up to @nr_pages
1690  * pages in the mapping starting at index @start and up to index @end
1691  * (inclusive).  The pages are placed at @pages.  find_get_pages_range() takes
1692  * a reference against the returned pages.
1693  *
1694  * The search returns a group of mapping-contiguous pages with ascending
1695  * indexes.  There may be holes in the indices due to not-present pages.
1696  * We also update @start to index the next page for the traversal.
1697  *
1698  * find_get_pages_range() returns the number of pages which were found. If this
1699  * number is smaller than @nr_pages, the end of specified range has been
1700  * reached.
1701  */
1702 unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
1703                               pgoff_t end, unsigned int nr_pages,
1704                               struct page **pages)
1705 {
1706         struct radix_tree_iter iter;
1707         void **slot;
1708         unsigned ret = 0;
1709 
1710         if (unlikely(!nr_pages))
1711                 return 0;
1712 
1713         rcu_read_lock();
1714         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, *start) {
1715                 struct page *head, *page;
1716 
1717                 if (iter.index > end)
1718                         break;
1719 repeat:
1720                 page = radix_tree_deref_slot(slot);
1721                 if (unlikely(!page))
1722                         continue;
1723 
1724                 if (radix_tree_exception(page)) {
1725                         if (radix_tree_deref_retry(page)) {
1726                                 slot = radix_tree_iter_retry(&iter);
1727                                 continue;
1728                         }
1729                         /*
1730                          * A shadow entry of a recently evicted page,
1731                          * or a swap entry from shmem/tmpfs.  Skip
1732                          * over it.
1733                          */
1734                         continue;
1735                 }
1736 
1737                 head = compound_head(page);
1738                 if (!page_cache_get_speculative(head))
1739                         goto repeat;
1740 
1741                 /* The page was split under us? */
1742                 if (compound_head(page) != head) {
1743                         put_page(head);
1744                         goto repeat;
1745                 }
1746 
1747                 /* Has the page moved? */
1748                 if (unlikely(page != *slot)) {
1749                         put_page(head);
1750                         goto repeat;
1751                 }
1752 
1753                 pages[ret] = page;
1754                 if (++ret == nr_pages) {
1755                         *start = pages[ret - 1]->index + 1;
1756                         goto out;
1757                 }
1758         }
1759 
1760         /*
1761          * We come here when there is no page beyond @end. We take care to not
1762          * overflow the index @start as it confuses some of the callers. This
1763          * breaks the iteration when there is page at index -1 but that is
1764          * already broken anyway.
1765          */
1766         if (end == (pgoff_t)-1)
1767                 *start = (pgoff_t)-1;
1768         else
1769                 *start = end + 1;
1770 out:
1771         rcu_read_unlock();
1772 
1773         return ret;
1774 }
1775 
1776 /**
1777  * find_get_pages_contig - gang contiguous pagecache lookup
1778  * @mapping:    The address_space to search
1779  * @index:      The starting page index
1780  * @nr_pages:   The maximum number of pages
1781  * @pages:      Where the resulting pages are placed
1782  *
1783  * find_get_pages_contig() works exactly like find_get_pages(), except
1784  * that the returned number of pages are guaranteed to be contiguous.
1785  *
1786  * find_get_pages_contig() returns the number of pages which were found.
1787  */
1788 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
1789                                unsigned int nr_pages, struct page **pages)
1790 {
1791         struct radix_tree_iter iter;
1792         void **slot;
1793         unsigned int ret = 0;
1794 
1795         if (unlikely(!nr_pages))
1796                 return 0;
1797 
1798         rcu_read_lock();
1799         radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
1800                 struct page *head, *page;
1801 repeat:
1802                 page = radix_tree_deref_slot(slot);
1803                 /* The hole, there no reason to continue */
1804                 if (unlikely(!page))
1805                         break;
1806 
1807                 if (radix_tree_exception(page)) {
1808                         if (radix_tree_deref_retry(page)) {
1809                                 slot = radix_tree_iter_retry(&iter);
1810                                 continue;
1811                         }
1812                         /*
1813                          * A shadow entry of a recently evicted page,
1814                          * or a swap entry from shmem/tmpfs.  Stop
1815                          * looking for contiguous pages.
1816                          */
1817                         break;
1818                 }
1819 
1820                 head = compound_head(page);
1821                 if (!page_cache_get_speculative(head))
1822                         goto repeat;
1823 
1824                 /* The page was split under us? */
1825                 if (compound_head(page) != head) {
1826                         put_page(head);
1827                         goto repeat;
1828                 }
1829 
1830                 /* Has the page moved? */
1831                 if (unlikely(page != *slot)) {
1832                         put_page(head);
1833                         goto repeat;
1834                 }
1835 
1836                 /*
1837                  * must check mapping and index after taking the ref.
1838                  * otherwise we can get both false positives and false
1839                  * negatives, which is just confusing to the caller.
1840                  */
1841                 if (page->mapping == NULL || page_to_pgoff(page) != iter.index) {
1842                         put_page(page);
1843                         break;
1844                 }
1845 
1846                 pages[ret] = page;
1847                 if (++ret == nr_pages)
1848                         break;
1849         }
1850         rcu_read_unlock();
1851         return ret;
1852 }
1853 EXPORT_SYMBOL(find_get_pages_contig);
1854 
1855 /**
1856  * find_get_pages_range_tag - find and return pages in given range matching @tag
1857  * @mapping:    the address_space to search
1858  * @index:      the starting page index
1859  * @end:        The final page index (inclusive)
1860  * @tag:        the tag index
1861  * @nr_pages:   the maximum number of pages
1862  * @pages:      where the resulting pages are placed
1863  *
1864  * Like find_get_pages, except we only return pages which are tagged with
1865  * @tag.   We update @index to index the next page for the traversal.
1866  */
1867 unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
1868                         pgoff_t end, int tag, unsigned int nr_pages,
1869                         struct page **pages)
1870 {
1871         struct radix_tree_iter iter;
1872         void **slot;
1873         unsigned ret = 0;
1874 
1875         if (unlikely(!nr_pages))
1876                 return 0;
1877 
1878         rcu_read_lock();
1879         radix_tree_for_each_tagged(slot, &mapping->page_tree,
1880                                    &iter, *index, tag) {
1881                 struct page *head, *page;
1882 
1883                 if (iter.index > end)
1884                         break;
1885 repeat:
1886                 page = radix_tree_deref_slot(slot);
1887                 if (unlikely(!page))
1888                         continue;
1889 
1890                 if (radix_tree_exception(page)) {
1891                         if (radix_tree_deref_retry(page)) {
1892                                 slot = radix_tree_iter_retry(&iter);
1893                                 continue;
1894                         }
1895                         /*
1896                          * A shadow entry of a recently evicted page.
1897                          *
1898                          * Those entries should never be tagged, but
1899                          * this tree walk is lockless and the tags are
1900                          * looked up in bulk, one radix tree node at a
1901                          * time, so there is a sizable window for page
1902                          * reclaim to evict a page we saw tagged.
1903                          *
1904                          * Skip over it.
1905                          */
1906                         continue;
1907                 }
1908 
1909                 head = compound_head(page);
1910                 if (!page_cache_get_speculative(head))
1911                         goto repeat;
1912 
1913                 /* The page was split under us? */
1914                 if (compound_head(page) != head) {
1915                         put_page(head);
1916                         goto repeat;
1917                 }
1918 
1919                 /* Has the page moved? */
1920                 if (unlikely(page != *slot)) {
1921                         put_page(head);
1922                         goto repeat;
1923                 }
1924 
1925                 pages[ret] = page;
1926                 if (++ret == nr_pages) {
1927                         *index = pages[ret - 1]->index + 1;
1928                         goto out;
1929                 }
1930         }
1931 
1932         /*
1933          * We come here when we got at @end. We take care to not overflow the
1934          * index @index as it confuses some of the callers. This breaks the
1935          * iteration when there is page at index -1 but that is already broken
1936          * anyway.
1937          */
1938         if (end == (pgoff_t)-1)
1939                 *index = (pgoff_t)-1;
1940         else
1941                 *index = end + 1;
1942 out:
1943         rcu_read_unlock();
1944 
1945         return ret;
1946 }
1947 EXPORT_SYMBOL(find_get_pages_range_tag);
1948 
1949 /**
1950  * find_get_entries_tag - find and return entries that match @tag
1951  * @mapping:    the address_space to search
1952  * @start:      the starting page cache index
1953  * @tag:        the tag index
1954  * @nr_entries: the maximum number of entries
1955  * @entries:    where the resulting entries are placed
1956  * @indices:    the cache indices corresponding to the entries in @entries
1957  *
1958  * Like find_get_entries, except we only return entries which are tagged with
1959  * @tag.
1960  */
1961 unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
1962                         int tag, unsigned int nr_entries,
1963                         struct page **entries, pgoff_t *indices)
1964 {
1965         void **slot;
1966         unsigned int ret = 0;
1967         struct radix_tree_iter iter;
1968 
1969         if (!nr_entries)
1970                 return 0;
1971 
1972         rcu_read_lock();
1973         radix_tree_for_each_tagged(slot, &mapping->page_tree,
1974                                    &iter, start, tag) {
1975                 struct page *head, *page;
1976 repeat:
1977                 page = radix_tree_deref_slot(slot);
1978                 if (unlikely(!page))
1979                         continue;
1980                 if (radix_tree_exception(page)) {
1981                         if (radix_tree_deref_retry(page)) {
1982                                 slot = radix_tree_iter_retry(&iter);
1983                                 continue;
1984                         }
1985 
1986                         /*
1987                          * A shadow entry of a recently evicted page, a swap
1988                          * entry from shmem/tmpfs or a DAX entry.  Return it
1989                          * without attempting to raise page count.
1990                          */
1991                         goto export;
1992                 }
1993 
1994                 head = compound_head(page);
1995                 if (!page_cache_get_speculative(head))
1996                         goto repeat;
1997 
1998                 /* The page was split under us? */
1999                 if (compound_head(page) != head) {
2000                         put_page(head);
2001                         goto repeat;
2002                 }
2003 
2004                 /* Has the page moved? */
2005                 if (unlikely(page != *slot)) {
2006                         put_page(head);
2007                         goto repeat;
2008                 }
2009 export:
2010                 indices[ret] = iter.index;
2011                 entries[ret] = page;
2012                 if (++ret == nr_entries)
2013                         break;
2014         }
2015         rcu_read_unlock();
2016         return ret;
2017 }
2018 EXPORT_SYMBOL(find_get_entries_tag);
2019 
2020 /*
2021  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
2022  * a _large_ part of the i/o request. Imagine the worst scenario:
2023  *
2024  *      ---R__________________________________________B__________
2025  *         ^ reading here                             ^ bad block(assume 4k)
2026  *
2027  * read(R) => miss => readahead(R...B) => media error => frustrating retries
2028  * => failing the whole request => read(R) => read(R+1) =>
2029  * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
2030  * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
2031  * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
2032  *
2033  * It is going insane. Fix it by quickly scaling down the readahead size.
2034  */
2035 static void shrink_readahead_size_eio(struct file *filp,
2036                                         struct file_ra_state *ra)
2037 {
2038         ra->ra_pages /= 4;
2039 }
2040 
2041 /**
2042  * generic_file_buffered_read - generic file read routine
2043  * @iocb:       the iocb to read
2044  * @iter:       data destination
2045  * @written:    already copied
2046  *
2047  * This is a generic file read routine, and uses the
2048  * mapping->a_ops->readpage() function for the actual low-level stuff.
2049  *
2050  * This is really ugly. But the goto's actually try to clarify some
2051  * of the logic when it comes to error handling etc.
2052  */
2053 static ssize_t generic_file_buffered_read(struct kiocb *iocb,
2054                 struct iov_iter *iter, ssize_t written)
2055 {
2056         struct file *filp = iocb->ki_filp;
2057         struct address_space *mapping = filp->f_mapping;
2058         struct inode *inode = mapping->host;
2059         struct file_ra_state *ra = &filp->f_ra;
2060         loff_t *ppos = &iocb->ki_pos;
2061         pgoff_t index;
2062         pgoff_t last_index;
2063         pgoff_t prev_index;
2064         unsigned long offset;      /* offset into pagecache page */
2065         unsigned int prev_offset;
2066         int error = 0;
2067 
2068         if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
2069                 return 0;
2070         iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
2071 
2072         index = *ppos >> PAGE_SHIFT;
2073         prev_index = ra->prev_pos >> PAGE_SHIFT;
2074         prev_offset = ra->prev_pos & (PAGE_SIZE-1);
2075         last_index = (*ppos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT;
2076         offset = *ppos & ~PAGE_MASK;
2077 
2078         for (;;) {
2079                 struct page *page;
2080                 pgoff_t end_index;
2081                 loff_t isize;
2082                 unsigned long nr, ret;
2083 
2084                 cond_resched();
2085 find_page:
2086                 if (fatal_signal_pending(current)) {
2087                         error = -EINTR;
2088                         goto out;
2089                 }
2090 
2091                 page = find_get_page(mapping, index);
2092                 if (!page) {
2093                         if (iocb->ki_flags & IOCB_NOWAIT)
2094                                 goto would_block;
2095                         page_cache_sync_readahead(mapping,
2096                                         ra, filp,
2097                                         index, last_index - index);
2098                         page = find_get_page(mapping, index);
2099                         if (unlikely(page == NULL))
2100                                 goto no_cached_page;
2101                 }
2102                 if (PageReadahead(page)) {
2103                         page_cache_async_readahead(mapping,
2104                                         ra, filp, page,
2105                                         index, last_index - index);
2106                 }
2107                 if (!PageUptodate(page)) {
2108                         if (iocb->ki_flags & IOCB_NOWAIT) {
2109                                 put_page(page);
2110                                 goto would_block;
2111                         }
2112 
2113                         /*
2114                          * See comment in do_read_cache_page on why
2115                          * wait_on_page_locked is used to avoid unnecessarily
2116                          * serialisations and why it's safe.
2117                          */
2118                         error = wait_on_page_locked_killable(page);
2119                         if (unlikely(error))
2120                                 goto readpage_error;
2121                         if (PageUptodate(page))
2122                                 goto page_ok;
2123 
2124                         if (inode->i_blkbits == PAGE_SHIFT ||
2125                                         !mapping->a_ops->is_partially_uptodate)
2126                                 goto page_not_up_to_date;
2127                         /* pipes can't handle partially uptodate pages */
2128                         if (unlikely(iter->type & ITER_PIPE))
2129                                 goto page_not_up_to_date;
2130                         if (!trylock_page(page))
2131                                 goto page_not_up_to_date;
2132                         /* Did it get truncated before we got the lock? */
2133                         if (!page->mapping)
2134                                 goto page_not_up_to_date_locked;
2135                         if (!mapping->a_ops->is_partially_uptodate(page,
2136                                                         offset, iter->count))
2137                                 goto page_not_up_to_date_locked;
2138                         unlock_page(page);
2139                 }
2140 page_ok:
2141                 /*
2142                  * i_size must be checked after we know the page is Uptodate.
2143                  *
2144                  * Checking i_size after the check allows us to calculate
2145                  * the correct value for "nr", which means the zero-filled
2146                  * part of the page is not copied back to userspace (unless
2147                  * another truncate extends the file - this is desired though).
2148                  */
2149 
2150                 isize = i_size_read(inode);
2151                 end_index = (isize - 1) >> PAGE_SHIFT;
2152                 if (unlikely(!isize || index > end_index)) {
2153                         put_page(page);
2154                         goto out;
2155                 }
2156 
2157                 /* nr is the maximum number of bytes to copy from this page */
2158                 nr = PAGE_SIZE;
2159                 if (index == end_index) {
2160                         nr = ((isize - 1) & ~PAGE_MASK) + 1;
2161                         if (nr <= offset) {
2162                                 put_page(page);
2163                                 goto out;
2164                         }
2165                 }
2166                 nr = nr - offset;
2167 
2168                 /* If users can be writing to this page using arbitrary
2169                  * virtual addresses, take care about potential aliasing
2170                  * before reading the page on the kernel side.
2171                  */
2172                 if (mapping_writably_mapped(mapping))
2173                         flush_dcache_page(page);
2174 
2175                 /*
2176                  * When a sequential read accesses a page several times,
2177                  * only mark it as accessed the first time.
2178                  */
2179                 if (prev_index != index || offset != prev_offset)
2180                         mark_page_accessed(page);
2181                 prev_index = index;
2182 
2183                 /*
2184                  * Ok, we have the page, and it's up-to-date, so
2185                  * now we can copy it to user space...
2186                  */
2187 
2188                 ret = copy_page_to_iter(page, offset, nr, iter);
2189                 offset += ret;
2190                 index += offset >> PAGE_SHIFT;
2191                 offset &= ~PAGE_MASK;
2192                 prev_offset = offset;
2193 
2194                 put_page(page);
2195                 written += ret;
2196                 if (!iov_iter_count(iter))
2197                         goto out;
2198                 if (ret < nr) {
2199                         error = -EFAULT;
2200                         goto out;
2201                 }
2202                 continue;
2203 
2204 page_not_up_to_date:
2205                 /* Get exclusive access to the page ... */
2206                 error = lock_page_killable(page);
2207                 if (unlikely(error))
2208                         goto readpage_error;
2209 
2210 page_not_up_to_date_locked:
2211                 /* Did it get truncated before we got the lock? */
2212                 if (!page->mapping) {
2213                         unlock_page(page);
2214                         put_page(page);
2215                         continue;
2216                 }
2217 
2218                 /* Did somebody else fill it already? */
2219                 if (PageUptodate(page)) {
2220                         unlock_page(page);
2221                         goto page_ok;
2222                 }
2223 
2224 readpage:
2225                 /*
2226                  * A previous I/O error may have been due to temporary
2227                  * failures, eg. multipath errors.
2228                  * PG_error will be set again if readpage fails.
2229                  */
2230                 ClearPageError(page);
2231                 /* Start the actual read. The read will unlock the page. */
2232                 error = mapping->a_ops->readpage(filp, page);
2233 
2234                 if (unlikely(error)) {
2235                         if (error == AOP_TRUNCATED_PAGE) {
2236                                 put_page(page);
2237                                 error = 0;
2238                                 goto find_page;
2239                         }
2240                         goto readpage_error;
2241                 }
2242 
2243                 if (!PageUptodate(page)) {
2244                         error = lock_page_killable(page);
2245                         if (unlikely(error))
2246                                 goto readpage_error;
2247                         if (!PageUptodate(page)) {
2248                                 if (page->mapping == NULL) {
2249                                         /*
2250                                          * invalidate_mapping_pages got it
2251                                          */
2252                                         unlock_page(page);
2253                                         put_page(page);
2254                                         goto find_page;
2255                                 }
2256                                 unlock_page(page);
2257                                 shrink_readahead_size_eio(filp, ra);
2258                                 error = -EIO;
2259                                 goto readpage_error;
2260                         }
2261                         unlock_page(page);
2262                 }
2263 
2264                 goto page_ok;
2265 
2266 readpage_error:
2267                 /* UHHUH! A synchronous read error occurred. Report it */
2268                 put_page(page);
2269                 goto out;
2270 
2271 no_cached_page:
2272                 /*
2273                  * Ok, it wasn't cached, so we need to create a new
2274                  * page..
2275                  */
2276                 page = page_cache_alloc(mapping);
2277                 if (!page) {
2278                         error = -ENOMEM;
2279                         goto out;
2280                 }
2281                 error = add_to_page_cache_lru(page, mapping, index,
2282                                 mapping_gfp_constraint(mapping, GFP_KERNEL));
2283                 if (error) {
2284                         put_page(page);
2285                         if (error == -EEXIST) {
2286                                 error = 0;
2287                                 goto find_page;
2288                         }
2289                         goto out;
2290                 }
2291                 goto readpage;
2292         }
2293 
2294 would_block:
2295         error = -EAGAIN;
2296 out:
2297         ra->prev_pos = prev_index;
2298         ra->prev_pos <<= PAGE_SHIFT;
2299         ra->prev_pos |= prev_offset;
2300 
2301         *ppos = ((loff_t)index << PAGE_SHIFT) + offset;
2302         file_accessed(filp);
2303         return written ? written : error;
2304 }
2305 
2306 /**
2307  * generic_file_read_iter - generic filesystem read routine
2308  * @iocb:       kernel I/O control block
2309  * @iter:       destination for the data read
2310  *
2311  * This is the "read_iter()" routine for all filesystems
2312  * that can use the page cache directly.
2313  */
2314 ssize_t
2315 generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
2316 {
2317         size_t count = iov_iter_count(iter);
2318         ssize_t retval = 0;
2319 
2320         if (!count)
2321                 goto out; /* skip atime */
2322 
2323         if (iocb->ki_flags & IOCB_DIRECT) {
2324                 struct file *file = iocb->ki_filp;
2325                 struct address_space *mapping = file->f_mapping;
2326                 struct inode *inode = mapping->host;
2327                 loff_t size;
2328 
2329                 size = i_size_read(inode);
2330                 if (iocb->ki_flags & IOCB_NOWAIT) {
2331                         if (filemap_range_has_page(mapping, iocb->ki_pos,
2332                                                    iocb->ki_pos + count - 1))
2333                                 return -EAGAIN;
2334                 } else {
2335                         retval = filemap_write_and_wait_range(mapping,
2336                                                 iocb->ki_pos,
2337                                                 iocb->ki_pos + count - 1);
2338                         if (retval < 0)
2339                                 goto out;
2340                 }
2341 
2342                 file_accessed(file);
2343 
2344                 retval = mapping->a_ops->direct_IO(iocb, iter);
2345                 if (retval >= 0) {
2346                         iocb->ki_pos += retval;
2347                         count -= retval;
2348                 }
2349                 iov_iter_revert(iter, count - iov_iter_count(iter));
2350 
2351                 /*
2352                  * Btrfs can have a short DIO read if we encounter
2353                  * compressed extents, so if there was an error, or if
2354                  * we've already read everything we wanted to, or if
2355                  * there was a short read because we hit EOF, go ahead
2356                  * and return.  Otherwise fallthrough to buffered io for
2357                  * the rest of the read.  Buffered reads will not work for
2358                  * DAX files, so don't bother trying.
2359                  */
2360                 if (retval < 0 || !count || iocb->ki_pos >= size ||
2361                     IS_DAX(inode))
2362                         goto out;
2363         }
2364 
2365         retval = generic_file_buffered_read(iocb, iter, retval);
2366 out:
2367         return retval;
2368 }
2369 EXPORT_SYMBOL(generic_file_read_iter);
2370 
2371 #ifdef CONFIG_MMU
2372 /**
2373  * page_cache_read - adds requested page to the page cache if not already there
2374  * @file:       file to read
2375  * @offset:     page index
2376  * @gfp_mask:   memory allocation flags
2377  *
2378  * This adds the requested page to the page cache if it isn't already there,
2379  * and schedules an I/O to read in its contents from disk.
2380  */
2381 static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask)
2382 {
2383         struct address_space *mapping = file->f_mapping;
2384         struct page *page;
2385         int ret;
2386 
2387         do {
2388                 page = __page_cache_alloc(gfp_mask);
2389                 if (!page)
2390                         return -ENOMEM;
2391 
2392                 ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask & GFP_KERNEL);
2393                 if (ret == 0)
2394                         ret = mapping->a_ops->readpage(file, page);
2395                 else if (ret == -EEXIST)
2396                         ret = 0; /* losing race to add is OK */
2397 
2398                 put_page(page);
2399 
2400         } while (ret == AOP_TRUNCATED_PAGE);
2401 
2402         return ret;
2403 }
2404 
2405 #define MMAP_LOTSAMISS  (100)
2406 
2407 /*
2408  * Synchronous readahead happens when we don't even find
2409  * a page in the page cache at all.
2410  */
2411 static void do_sync_mmap_readahead(struct vm_area_struct *vma,
2412                                    struct file_ra_state *ra,
2413                                    struct file *file,
2414                                    pgoff_t offset)
2415 {
2416         struct address_space *mapping = file->f_mapping;
2417 
2418         /* If we don't want any read-ahead, don't bother */
2419         if (vma->vm_flags & VM_RAND_READ)
2420                 return;
2421         if (!ra->ra_pages)
2422                 return;
2423 
2424         if (vma->vm_flags & VM_SEQ_READ) {
2425                 page_cache_sync_readahead(mapping, ra, file, offset,
2426                                           ra->ra_pages);
2427                 return;
2428         }
2429 
2430         /* Avoid banging the cache line if not needed */
2431         if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
2432                 ra->mmap_miss++;
2433 
2434         /*
2435          * Do we miss much more than hit in this file? If so,
2436          * stop bothering with read-ahead. It will only hurt.
2437          */
2438         if (ra->mmap_miss > MMAP_LOTSAMISS)
2439                 return;
2440 
2441         /*
2442          * mmap read-around
2443          */
2444         ra->start = max_t(long, 0, offset - ra->ra_pages / 2);
2445         ra->size = ra->ra_pages;
2446         ra->async_size = ra->ra_pages / 4;
2447         ra_submit(ra, mapping, file);
2448 }
2449 
2450 /*
2451  * Asynchronous readahead happens when we find the page and PG_readahead,
2452  * so we want to possibly extend the readahead further..
2453  */
2454 static void do_async_mmap_readahead(struct vm_area_struct *vma,
2455                                     struct file_ra_state *ra,
2456                                     struct file *file,
2457                                     struct page *page,
2458                                     pgoff_t offset)
2459 {
2460         struct address_space *mapping = file->f_mapping;
2461 
2462         /* If we don't want any read-ahead, don't bother */
2463         if (vma->vm_flags & VM_RAND_READ)
2464                 return;
2465         if (ra->mmap_miss > 0)
2466                 ra->mmap_miss--;
2467         if (PageReadahead(page))
2468                 page_cache_async_readahead(mapping, ra, file,
2469                                            page, offset, ra->ra_pages);
2470 }
2471 
2472 /**
2473  * filemap_fault - read in file data for page fault handling
2474  * @vmf:        struct vm_fault containing details of the fault
2475  *
2476  * filemap_fault() is invoked via the vma operations vector for a
2477  * mapped memory region to read in file data during a page fault.
2478  *
2479  * The goto's are kind of ugly, but this streamlines the normal case of having
2480  * it in the page cache, and handles the special cases reasonably without
2481  * having a lot of duplicated code.
2482  *
2483  * vma->vm_mm->mmap_sem must be held on entry.
2484  *
2485  * If our return value has VM_FAULT_RETRY set, it's because
2486  * lock_page_or_retry() returned 0.
2487  * The mmap_sem has usually been released in this case.
2488  * See __lock_page_or_retry() for the exception.
2489  *
2490  * If our return value does not have VM_FAULT_RETRY set, the mmap_sem
2491  * has not been released.
2492  *
2493  * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
2494  */
2495 int filemap_fault(struct vm_fault *vmf)
2496 {
2497         int error;
2498         struct file *file = vmf->vma->vm_file;
2499         struct address_space *mapping = file->f_mapping;
2500         struct file_ra_state *ra = &file->f_ra;
2501         struct inode *inode = mapping->host;
2502         pgoff_t offset = vmf->pgoff;
2503         pgoff_t max_off;
2504         struct page *page;
2505         int ret = 0;
2506 
2507         max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
2508         if (unlikely(offset >= max_off))
2509                 return VM_FAULT_SIGBUS;
2510 
2511         /*
2512          * Do we have something in the page cache already?
2513          */
2514         page = find_get_page(mapping, offset);
2515         if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
2516                 /*
2517                  * We found the page, so try async readahead before
2518                  * waiting for the lock.
2519                  */
2520                 do_async_mmap_readahead(vmf->vma, ra, file, page, offset);
2521         } else if (!page) {
2522                 /* No page in the page cache at all */
2523                 do_sync_mmap_readahead(vmf->vma, ra, file, offset);
2524                 count_vm_event(PGMAJFAULT);
2525                 count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
2526                 ret = VM_FAULT_MAJOR;
2527 retry_find:
2528                 page = find_get_page(mapping, offset);
2529                 if (!page)
2530                         goto no_cached_page;
2531         }
2532 
2533         if (!lock_page_or_retry(page, vmf->vma->vm_mm, vmf->flags)) {
2534                 put_page(page);
2535                 return ret | VM_FAULT_RETRY;
2536         }
2537 
2538         /* Did it get truncated? */
2539         if (unlikely(page->mapping != mapping)) {
2540                 unlock_page(page);
2541                 put_page(page);
2542                 goto retry_find;
2543         }
2544         VM_BUG_ON_PAGE(page->index != offset, page);
2545 
2546         /*
2547          * We have a locked page in the page cache, now we need to check
2548          * that it's up-to-date. If not, it is going to be due to an error.
2549          */
2550         if (unlikely(!PageUptodate(page)))
2551                 goto page_not_uptodate;
2552 
2553         /*
2554          * Found the page and have a reference on it.
2555          * We must recheck i_size under page lock.
2556          */
2557         max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
2558         if (unlikely(offset >= max_off)) {
2559                 unlock_page(page);
2560                 put_page(page);
2561                 return VM_FAULT_SIGBUS;
2562         }
2563 
2564         vmf->page = page;
2565         return ret | VM_FAULT_LOCKED;
2566 
2567 no_cached_page:
2568         /*
2569          * We're only likely to ever get here if MADV_RANDOM is in
2570          * effect.
2571          */
2572         error = page_cache_read(file, offset, vmf->gfp_mask);
2573 
2574         /*
2575          * The page we want has now been added to the page cache.
2576          * In the unlikely event that someone removed it in the
2577          * meantime, we'll just come back here and read it again.
2578          */
2579         if (error >= 0)
2580                 goto retry_find;
2581 
2582         /*
2583          * An error return from page_cache_read can result if the
2584          * system is low on memory, or a problem occurs while trying
2585          * to schedule I/O.
2586          */
2587         if (error == -ENOMEM)
2588                 return VM_FAULT_OOM;
2589         return VM_FAULT_SIGBUS;
2590 
2591 page_not_uptodate:
2592         /*
2593          * Umm, take care of errors if the page isn't up-to-date.
2594          * Try to re-read it _once_. We do this synchronously,
2595          * because there really aren't any performance issues here
2596          * and we need to check for errors.
2597          */
2598         ClearPageError(page);
2599         error = mapping->a_ops->readpage(file, page);
2600         if (!error) {
2601                 wait_on_page_locked(page);
2602                 if (!PageUptodate(page))
2603                         error = -EIO;
2604         }
2605         put_page(page);
2606 
2607         if (!error || error == AOP_TRUNCATED_PAGE)
2608                 goto retry_find;
2609 
2610         /* Things didn't work out. Return zero to tell the mm layer so. */
2611         shrink_readahead_size_eio(file, ra);
2612         return VM_FAULT_SIGBUS;
2613 }
2614 EXPORT_SYMBOL(filemap_fault);
2615 
2616 void filemap_map_pages(struct vm_fault *vmf,
2617                 pgoff_t start_pgoff, pgoff_t end_pgoff)
2618 {
2619         struct radix_tree_iter iter;
2620         void **slot;
2621         struct file *file = vmf->vma->vm_file;
2622         struct address_space *mapping = file->f_mapping;
2623         pgoff_t last_pgoff = start_pgoff;
2624         unsigned long max_idx;
2625         struct page *head, *page;
2626 
2627         rcu_read_lock();
2628         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter,
2629                         start_pgoff) {
2630                 if (iter.index > end_pgoff)
2631                         break;
2632 repeat:
2633                 page = radix_tree_deref_slot(slot);
2634                 if (unlikely(!page))
2635                         goto next;
2636                 if (radix_tree_exception(page)) {
2637                         if (radix_tree_deref_retry(page)) {
2638                                 slot = radix_tree_iter_retry(&iter);
2639                                 continue;
2640                         }
2641                         goto next;
2642                 }
2643 
2644                 head = compound_head(page);
2645                 if (!page_cache_get_speculative(head))
2646                         goto repeat;
2647 
2648                 /* The page was split under us? */
2649                 if (compound_head(page) != head) {
2650                         put_page(head);
2651                         goto repeat;
2652                 }
2653 
2654                 /* Has the page moved? */
2655                 if (unlikely(page != *slot)) {
2656                         put_page(head);
2657                         goto repeat;
2658                 }
2659 
2660                 if (!PageUptodate(page) ||
2661                                 PageReadahead(page) ||
2662                                 PageHWPoison(page))
2663                         goto skip;
2664                 if (!trylock_page(page))
2665                         goto skip;
2666 
2667                 if (page->mapping != mapping || !PageUptodate(page))
2668                         goto unlock;
2669 
2670                 max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
2671                 if (page->index >= max_idx)
2672                         goto unlock;
2673 
2674                 if (file->f_ra.mmap_miss > 0)
2675                         file->f_ra.mmap_miss--;
2676 
2677                 vmf->address += (iter.index - last_pgoff) << PAGE_SHIFT;
2678                 if (vmf->pte)
2679                         vmf->pte += iter.index - last_pgoff;
2680                 last_pgoff = iter.index;
2681                 if (alloc_set_pte(vmf, NULL, page))
2682                         goto unlock;
2683                 unlock_page(page);
2684                 goto next;
2685 unlock:
2686                 unlock_page(page);
2687 skip:
2688                 put_page(page);
2689 next:
2690                 /* Huge page is mapped? No need to proceed. */
2691                 if (pmd_trans_huge(*vmf->pmd))
2692                         break;
2693                 if (iter.index == end_pgoff)
2694                         break;
2695         }
2696         rcu_read_unlock();
2697 }
2698 EXPORT_SYMBOL(filemap_map_pages);
2699 
2700 int filemap_page_mkwrite(struct vm_fault *vmf)
2701 {
2702         struct page *page = vmf->page;
2703         struct inode *inode = file_inode(vmf->vma->vm_file);
2704         int ret = VM_FAULT_LOCKED;
2705 
2706         sb_start_pagefault(inode->i_sb);
2707         file_update_time(vmf->vma->vm_file);
2708         lock_page(page);
2709         if (page->mapping != inode->i_mapping) {
2710                 unlock_page(page);
2711                 ret = VM_FAULT_NOPAGE;
2712                 goto out;
2713         }
2714         /*
2715          * We mark the page dirty already here so that when freeze is in
2716          * progress, we are guaranteed that writeback during freezing will
2717          * see the dirty page and writeprotect it again.
2718          */
2719         set_page_dirty(page);
2720         wait_for_stable_page(page);
2721 out:
2722         sb_end_pagefault(inode->i_sb);
2723         return ret;
2724 }
2725 EXPORT_SYMBOL(filemap_page_mkwrite);
2726 
2727 const struct vm_operations_struct generic_file_vm_ops = {
2728         .fault          = filemap_fault,
2729         .map_pages      = filemap_map_pages,
2730         .page_mkwrite   = filemap_page_mkwrite,
2731 };
2732 
2733 /* This is used for a general mmap of a disk file */
2734 
2735 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
2736 {
2737         struct address_space *mapping = file->f_mapping;
2738 
2739         if (!mapping->a_ops->readpage)
2740                 return -ENOEXEC;
2741         file_accessed(file);
2742         vma->vm_ops = &generic_file_vm_ops;
2743         return 0;
2744 }
2745 
2746 /*
2747  * This is for filesystems which do not implement ->writepage.
2748  */
2749 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
2750 {
2751         if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
2752                 return -EINVAL;
2753         return generic_file_mmap(file, vma);
2754 }
2755 #else
2756 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
2757 {
2758         return -ENOSYS;
2759 }
2760 int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
2761 {
2762         return -ENOSYS;
2763 }
2764 #endif /* CONFIG_MMU */
2765 
2766 EXPORT_SYMBOL(generic_file_mmap);
2767 EXPORT_SYMBOL(generic_file_readonly_mmap);
2768 
2769 static struct page *wait_on_page_read(struct page *page)
2770 {
2771         if (!IS_ERR(page)) {
2772                 wait_on_page_locked(page);
2773                 if (!PageUptodate(page)) {
2774                         put_page(page);
2775                         page = ERR_PTR(-EIO);
2776                 }
2777         }
2778         return page;
2779 }
2780 
2781 static struct page *do_read_cache_page(struct address_space *mapping,
2782                                 pgoff_t index,
2783                                 int (*filler)(void *, struct page *),
2784                                 void *data,
2785                                 gfp_t gfp)
2786 {
2787         struct page *page;
2788         int err;
2789 repeat:
2790         page = find_get_page(mapping, index);
2791         if (!page) {
2792                 page = __page_cache_alloc(gfp);
2793                 if (!page)
2794                         return ERR_PTR(-ENOMEM);
2795                 err = add_to_page_cache_lru(page, mapping, index, gfp);
2796                 if (unlikely(err)) {
2797                         put_page(page);
2798                         if (err == -EEXIST)
2799                                 goto repeat;
2800                         /* Presumably ENOMEM for radix tree node */
2801                         return ERR_PTR(err);
2802                 }
2803 
2804 filler:
2805                 err = filler(data, page);
2806                 if (err < 0) {
2807                         put_page(page);
2808                         return ERR_PTR(err);
2809                 }
2810 
2811                 page = wait_on_page_read(page);
2812                 if (IS_ERR(page))
2813                         return page;
2814                 goto out;
2815         }
2816         if (PageUptodate(page))
2817                 goto out;
2818 
2819         /*
2820          * Page is not up to date and may be locked due one of the following
2821          * case a: Page is being filled and the page lock is held
2822          * case b: Read/write error clearing the page uptodate status
2823          * case c: Truncation in progress (page locked)
2824          * case d: Reclaim in progress
2825          *
2826          * Case a, the page will be up to date when the page is unlocked.
2827          *    There is no need to serialise on the page lock here as the page
2828          *    is pinned so the lock gives no additional protection. Even if the
2829          *    the page is truncated, the data is still valid if PageUptodate as
2830          *    it's a race vs truncate race.
2831          * Case b, the page will not be up to date
2832          * Case c, the page may be truncated but in itself, the data may still
2833          *    be valid after IO completes as it's a read vs truncate race. The
2834          *    operation must restart if the page is not uptodate on unlock but
2835          *    otherwise serialising on page lock to stabilise the mapping gives
2836          *    no additional guarantees to the caller as the page lock is
2837          *    released before return.
2838          * Case d, similar to truncation. If reclaim holds the page lock, it
2839          *    will be a race with remove_mapping that determines if the mapping
2840          *    is valid on unlock but otherwise the data is valid and there is
2841          *    no need to serialise with page lock.
2842          *
2843          * As the page lock gives no additional guarantee, we optimistically
2844          * wait on the page to be unlocked and check if it's up to date and
2845          * use the page if it is. Otherwise, the page lock is required to
2846          * distinguish between the different cases. The motivation is that we
2847          * avoid spurious serialisations and wakeups when multiple processes
2848          * wait on the same page for IO to complete.
2849          */
2850         wait_on_page_locked(page);
2851         if (PageUptodate(page))
2852                 goto out;
2853 
2854         /* Distinguish between all the cases under the safety of the lock */
2855         lock_page(page);
2856 
2857         /* Case c or d, restart the operation */
2858         if (!page->mapping) {
2859                 unlock_page(page);
2860                 put_page(page);
2861                 goto repeat;
2862         }
2863 
2864         /* Someone else locked and filled the page in a very small window */
2865         if (PageUptodate(page)) {
2866                 unlock_page(page);
2867                 goto out;
2868         }
2869         goto filler;
2870 
2871 out:
2872         mark_page_accessed(page);
2873         return page;
2874 }
2875 
2876 /**
2877  * read_cache_page - read into page cache, fill it if needed
2878  * @mapping:    the page's address_space
2879  * @index:      the page index
2880  * @filler:     function to perform the read
2881  * @data:       first arg to filler(data, page) function, often left as NULL
2882  *
2883  * Read into the page cache. If a page already exists, and PageUptodate() is
2884  * not set, try to fill the page and wait for it to become unlocked.
2885  *
2886  * If the page does not get brought uptodate, return -EIO.
2887  */
2888 struct page *read_cache_page(struct address_space *mapping,
2889                                 pgoff_t index,
2890                                 int (*filler)(void *, struct page *),
2891                                 void *data)
2892 {
2893         return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
2894 }
2895 EXPORT_SYMBOL(read_cache_page);
2896 
2897 /**
2898  * read_cache_page_gfp - read into page cache, using specified page allocation flags.
2899  * @mapping:    the page's address_space
2900  * @index:      the page index
2901  * @gfp:        the page allocator flags to use if allocating
2902  *
2903  * This is the same as "read_mapping_page(mapping, index, NULL)", but with
2904  * any new page allocations done using the specified allocation flags.
2905  *
2906  * If the page does not get brought uptodate, return -EIO.
2907  */
2908 struct page *read_cache_page_gfp(struct address_space *mapping,
2909                                 pgoff_t index,
2910                                 gfp_t gfp)
2911 {
2912         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
2913 
2914         return do_read_cache_page(mapping, index, filler, NULL, gfp);
2915 }
2916 EXPORT_SYMBOL(read_cache_page_gfp);
2917 
2918 /*
2919  * Performs necessary checks before doing a write
2920  *
2921  * Can adjust writing position or amount of bytes to write.
2922  * Returns appropriate error code that caller should return or
2923  * zero in case that write should be allowed.
2924  */
2925 inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
2926 {
2927         struct file *file = iocb->ki_filp;
2928         struct inode *inode = file->f_mapping->host;
2929         unsigned long limit = rlimit(RLIMIT_FSIZE);
2930         loff_t pos;
2931 
2932         if (!iov_iter_count(from))
2933                 return 0;
2934 
2935         /* FIXME: this is for backwards compatibility with 2.4 */
2936         if (iocb->ki_flags & IOCB_APPEND)
2937                 iocb->ki_pos = i_size_read(inode);
2938 
2939         pos = iocb->ki_pos;
2940 
2941         if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
2942                 return -EINVAL;
2943 
2944         if (limit != RLIM_INFINITY) {
2945                 if (iocb->ki_pos >= limit) {
2946                         send_sig(SIGXFSZ, current, 0);
2947                         return -EFBIG;
2948                 }
2949                 iov_iter_truncate(from, limit - (unsigned long)pos);
2950         }
2951 
2952         /*
2953          * LFS rule
2954          */
2955         if (unlikely(pos + iov_iter_count(from) > MAX_NON_LFS &&
2956                                 !(file->f_flags & O_LARGEFILE))) {
2957                 if (pos >= MAX_NON_LFS)
2958                         return -EFBIG;
2959                 iov_iter_truncate(from, MAX_NON_LFS - (unsigned long)pos);
2960         }
2961 
2962         /*
2963          * Are we about to exceed the fs block limit ?
2964          *
2965          * If we have written data it becomes a short write.  If we have
2966          * exceeded without writing data we send a signal and return EFBIG.
2967          * Linus frestrict idea will clean these up nicely..
2968          */
2969         if (unlikely(pos >= inode->i_sb->s_maxbytes))
2970                 return -EFBIG;
2971 
2972         iov_iter_truncate(from, inode->i_sb->s_maxbytes - pos);
2973         return iov_iter_count(from);
2974 }
2975 EXPORT_SYMBOL(generic_write_checks);
2976 
2977 int pagecache_write_begin(struct file *file, struct address_space *mapping,
2978                                 loff_t pos, unsigned len, unsigned flags,
2979                                 struct page **pagep, void **fsdata)
2980 {
2981         const struct address_space_operations *aops = mapping->a_ops;
2982 
2983         return aops->write_begin(file, mapping, pos, len, flags,
2984                                                         pagep, fsdata);
2985 }
2986 EXPORT_SYMBOL(pagecache_write_begin);
2987 
2988 int pagecache_write_end(struct file *file, struct address_space *mapping,
2989                                 loff_t pos, unsigned len, unsigned copied,
2990                                 struct page *page, void *fsdata)
2991 {
2992         const struct address_space_operations *aops = mapping->a_ops;
2993 
2994         return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
2995 }
2996 EXPORT_SYMBOL(pagecache_write_end);
2997 
2998 ssize_t
2999 generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
3000 {
3001         struct file     *file = iocb->ki_filp;
3002         struct address_space *mapping = file->f_mapping;
3003         struct inode    *inode = mapping->host;
3004         loff_t          pos = iocb->ki_pos;
3005         ssize_t         written;
3006         size_t          write_len;
3007         pgoff_t         end;
3008 
3009         write_len = iov_iter_count(from);
3010         end = (pos + write_len - 1) >> PAGE_SHIFT;
3011 
3012         if (iocb->ki_flags & IOCB_NOWAIT) {
3013                 /* If there are pages to writeback, return */
3014                 if (filemap_range_has_page(inode->i_mapping, pos,
3015                                            pos + iov_iter_count(from)))
3016                         return -EAGAIN;
3017         } else {
3018                 written = filemap_write_and_wait_range(mapping, pos,
3019                                                         pos + write_len - 1);
3020                 if (written)
3021                         goto out;
3022         }
3023 
3024         /*
3025          * After a write we want buffered reads to be sure to go to disk to get
3026          * the new data.  We invalidate clean cached page from the region we're
3027          * about to write.  We do this *before* the write so that we can return
3028          * without clobbering -EIOCBQUEUED from ->direct_IO().
3029          */
3030         written = invalidate_inode_pages2_range(mapping,
3031                                         pos >> PAGE_SHIFT, end);
3032         /*
3033          * If a page can not be invalidated, return 0 to fall back
3034          * to buffered write.
3035          */
3036         if (written) {
3037                 if (written == -EBUSY)
3038                         return 0;
3039                 goto out;
3040         }
3041 
3042         written = mapping->a_ops->direct_IO(iocb, from);
3043 
3044         /*
3045          * Finally, try again to invalidate clean pages which might have been
3046          * cached by non-direct readahead, or faulted in by get_user_pages()
3047          * if the source of the write was an mmap'ed region of the file
3048          * we're writing.  Either one is a pretty crazy thing to do,
3049          * so we don't support it 100%.  If this invalidation
3050          * fails, tough, the write still worked...
3051          *
3052          * Most of the time we do not need this since dio_complete() will do
3053          * the invalidation for us. However there are some file systems that
3054          * do not end up with dio_complete() being called, so let's not break
3055          * them by removing it completely
3056          */
3057         if (mapping->nrpages)
3058                 invalidate_inode_pages2_range(mapping,
3059                                         pos >> PAGE_SHIFT, end);
3060 
3061         if (written > 0) {
3062                 pos += written;
3063                 write_len -= written;
3064                 if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
3065                         i_size_write(inode, pos);
3066                         mark_inode_dirty(inode);
3067                 }
3068                 iocb->ki_pos = pos;
3069         }
3070         iov_iter_revert(from, write_len - iov_iter_count(from));
3071 out:
3072         return written;
3073 }
3074 EXPORT_SYMBOL(generic_file_direct_write);
3075 
3076 /*
3077  * Find or create a page at the given pagecache position. Return the locked
3078  * page. This function is specifically for buffered writes.
3079  */
3080 struct page *grab_cache_page_write_begin(struct address_space *mapping,
3081                                         pgoff_t index, unsigned flags)
3082 {
3083         struct page *page;
3084         int fgp_flags = FGP_LOCK|FGP_WRITE|FGP_CREAT;
3085 
3086         if (flags & AOP_FLAG_NOFS)
3087                 fgp_flags |= FGP_NOFS;
3088 
3089         page = pagecache_get_page(mapping, index, fgp_flags,
3090                         mapping_gfp_mask(mapping));
3091         if (page)
3092                 wait_for_stable_page(page);
3093 
3094         return page;
3095 }
3096 EXPORT_SYMBOL(grab_cache_page_write_begin);
3097 
3098 ssize_t generic_perform_write(struct file *file,
3099                                 struct iov_iter *i, loff_t pos)
3100 {
3101         struct address_space *mapping = file->f_mapping;
3102         const struct address_space_operations *a_ops = mapping->a_ops;
3103         long status = 0;
3104         ssize_t written = 0;
3105         unsigned int flags = 0;
3106 
3107         do {
3108                 struct page *page;
3109                 unsigned long offset;   /* Offset into pagecache page */
3110                 unsigned long bytes;    /* Bytes to write to page */
3111                 size_t copied;          /* Bytes copied from user */
3112                 void *fsdata;
3113 
3114                 offset = (pos & (PAGE_SIZE - 1));
3115                 bytes = min_t(unsigned long, PAGE_SIZE - offset,
3116                                                 iov_iter_count(i));
3117 
3118 again:
3119                 /*
3120                  * Bring in the user page that we will copy from _first_.
3121                  * Otherwise there's a nasty deadlock on copying from the
3122                  * same page as we're writing to, without it being marked
3123                  * up-to-date.
3124                  *
3125                  * Not only is this an optimisation, but it is also required
3126                  * to check that the address is actually valid, when atomic
3127                  * usercopies are used, below.
3128                  */
3129                 if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
3130                         status = -EFAULT;
3131                         break;
3132                 }
3133 
3134                 if (fatal_signal_pending(current)) {
3135                         status = -EINTR;
3136                         break;
3137                 }
3138 
3139                 status = a_ops->write_begin(file, mapping, pos, bytes, flags,
3140                                                 &page, &fsdata);
3141                 if (unlikely(status < 0))
3142                         break;
3143 
3144                 if (mapping_writably_mapped(mapping))
3145                         flush_dcache_page(page);
3146 
3147                 copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
3148                 flush_dcache_page(page);
3149 
3150                 status = a_ops->write_end(file, mapping, pos, bytes, copied,
3151                                                 page, fsdata);
3152                 if (unlikely(status < 0))
3153                         break;
3154                 copied = status;
3155 
3156                 cond_resched();
3157 
3158                 iov_iter_advance(i, copied);
3159                 if (unlikely(copied == 0)) {
3160                         /*
3161                          * If we were unable to copy any data at all, we must
3162                          * fall back to a single segment length write.
3163                          *
3164                          * If we didn't fallback here, we could livelock
3165                          * because not all segments in the iov can be copied at
3166                          * once without a pagefault.
3167                          */
3168                         bytes = min_t(unsigned long, PAGE_SIZE - offset,
3169                                                 iov_iter_single_seg_count(i));
3170                         goto again;
3171                 }
3172                 pos += copied;
3173                 written += copied;
3174 
3175                 balance_dirty_pages_ratelimited(mapping);
3176         } while (iov_iter_count(i));
3177 
3178         return written ? written : status;
3179 }
3180 EXPORT_SYMBOL(generic_perform_write);
3181 
3182 /**
3183  * __generic_file_write_iter - write data to a file
3184  * @iocb:       IO state structure (file, offset, etc.)
3185  * @from:       iov_iter with data to write
3186  *
3187  * This function does all the work needed for actually writing data to a
3188  * file. It does all basic checks, removes SUID from the file, updates
3189  * modification times and calls proper subroutines depending on whether we
3190  * do direct IO or a standard buffered write.
3191  *
3192  * It expects i_mutex to be grabbed unless we work on a block device or similar
3193  * object which does not need locking at all.
3194  *
3195  * This function does *not* take care of syncing data in case of O_SYNC write.
3196  * A caller has to handle it. This is mainly due to the fact that we want to
3197  * avoid syncing under i_mutex.
3198  */
3199 ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
3200 {
3201         struct file *file = iocb->ki_filp;
3202         struct address_space * mapping = file->f_mapping;
3203         struct inode    *inode = mapping->host;
3204         ssize_t         written = 0;
3205         ssize_t         err;
3206         ssize_t         status;
3207 
3208         /* We can write back this queue in page reclaim */
3209         current->backing_dev_info = inode_to_bdi(inode);
3210         err = file_remove_privs(file);
3211         if (err)
3212                 goto out;
3213 
3214         err = file_update_time(file);
3215         if (err)
3216                 goto out;
3217 
3218         if (iocb->ki_flags & IOCB_DIRECT) {
3219                 loff_t pos, endbyte;
3220 
3221                 written = generic_file_direct_write(iocb, from);
3222                 /*
3223                  * If the write stopped short of completing, fall back to
3224                  * buffered writes.  Some filesystems do this for writes to
3225                  * holes, for example.  For DAX files, a buffered write will
3226                  * not succeed (even if it did, DAX does not handle dirty
3227                  * page-cache pages correctly).
3228                  */
3229                 if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
3230                         goto out;
3231 
3232                 status = generic_perform_write(file, from, pos = iocb->ki_pos);
3233                 /*
3234                  * If generic_perform_write() returned a synchronous error
3235                  * then we want to return the number of bytes which were
3236                  * direct-written, or the error code if that was zero.  Note
3237                  * that this differs from normal direct-io semantics, which
3238                  * will return -EFOO even if some bytes were written.
3239                  */
3240                 if (unlikely(status < 0)) {
3241                         err = status;
3242                         goto out;
3243                 }
3244                 /*
3245                  * We need to ensure that the page cache pages are written to
3246                  * disk and invalidated to preserve the expected O_DIRECT
3247                  * semantics.
3248                  */
3249                 endbyte = pos + status - 1;
3250                 err = filemap_write_and_wait_range(mapping, pos, endbyte);
3251                 if (err == 0) {
3252                         iocb->ki_pos = endbyte + 1;
3253                         written += status;
3254                         invalidate_mapping_pages(mapping,
3255                                                  pos >> PAGE_SHIFT,
3256                                                  endbyte >> PAGE_SHIFT);
3257                 } else {
3258                         /*
3259                          * We don't know how much we wrote, so just return
3260                          * the number of bytes which were direct-written
3261                          */
3262                 }
3263         } else {
3264                 written = generic_perform_write(file, from, iocb->ki_pos);
3265                 if (likely(written > 0))
3266                         iocb->ki_pos += written;
3267         }
3268 out:
3269         current->backing_dev_info = NULL;
3270         return written ? written : err;
3271 }
3272 EXPORT_SYMBOL(__generic_file_write_iter);
3273 
3274 /**
3275  * generic_file_write_iter - write data to a file
3276  * @iocb:       IO state structure
3277  * @from:       iov_iter with data to write
3278  *
3279  * This is a wrapper around __generic_file_write_iter() to be used by most
3280  * filesystems. It takes care of syncing the file in case of O_SYNC file
3281  * and acquires i_mutex as needed.
3282  */
3283 ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
3284 {
3285         struct file *file = iocb->ki_filp;
3286         struct inode *inode = file->f_mapping->host;
3287         ssize_t ret;
3288 
3289         inode_lock(inode);
3290         ret = generic_write_checks(iocb, from);
3291         if (ret > 0)
3292                 ret = __generic_file_write_iter(iocb, from);
3293         inode_unlock(inode);
3294 
3295         if (ret > 0)
3296                 ret = generic_write_sync(iocb, ret);
3297         return ret;
3298 }
3299 EXPORT_SYMBOL(generic_file_write_iter);
3300 
3301 /**
3302  * try_to_release_page() - release old fs-specific metadata on a page
3303  *
3304  * @page: the page which the kernel is trying to free
3305  * @gfp_mask: memory allocation flags (and I/O mode)
3306  *
3307  * The address_space is to try to release any data against the page
3308  * (presumably at page->private).  If the release was successful, return '1'.
3309  * Otherwise return zero.
3310  *
3311  * This may also be called if PG_fscache is set on a page, indicating that the
3312  * page is known to the local caching routines.
3313  *
3314  * The @gfp_mask argument specifies whether I/O may be performed to release
3315  * this page (__GFP_IO), and whether the call may block (__GFP_RECLAIM & __GFP_FS).
3316  *
3317  */
3318 int try_to_release_page(struct page *page, gfp_t gfp_mask)
3319 {
3320         struct address_space * const mapping = page->mapping;
3321 
3322         BUG_ON(!PageLocked(page));
3323         if (PageWriteback(page))
3324                 return 0;
3325 
3326         if (mapping && mapping->a_ops->releasepage)
3327                 return mapping->a_ops->releasepage(page, gfp_mask);
3328         return try_to_free_buffers(page);
3329 }
3330 
3331 EXPORT_SYMBOL(try_to_release_page);
3332 

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