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TOMOYO Linux Cross Reference
Linux/fs/afs/write.c

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  1 /* handling of writes to regular files and writing back to the server
  2  *
  3  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
  4  * Written by David Howells (dhowells@redhat.com)
  5  *
  6  * This program is free software; you can redistribute it and/or
  7  * modify it under the terms of the GNU General Public License
  8  * as published by the Free Software Foundation; either version
  9  * 2 of the License, or (at your option) any later version.
 10  */
 11 #include <linux/backing-dev.h>
 12 #include <linux/slab.h>
 13 #include <linux/fs.h>
 14 #include <linux/pagemap.h>
 15 #include <linux/writeback.h>
 16 #include <linux/pagevec.h>
 17 #include "internal.h"
 18 
 19 static int afs_write_back_from_locked_page(struct afs_writeback *wb,
 20                                            struct page *page);
 21 
 22 /*
 23  * mark a page as having been made dirty and thus needing writeback
 24  */
 25 int afs_set_page_dirty(struct page *page)
 26 {
 27         _enter("");
 28         return __set_page_dirty_nobuffers(page);
 29 }
 30 
 31 /*
 32  * unlink a writeback record because its usage has reached zero
 33  * - must be called with the wb->vnode->writeback_lock held
 34  */
 35 static void afs_unlink_writeback(struct afs_writeback *wb)
 36 {
 37         struct afs_writeback *front;
 38         struct afs_vnode *vnode = wb->vnode;
 39 
 40         list_del_init(&wb->link);
 41         if (!list_empty(&vnode->writebacks)) {
 42                 /* if an fsync rises to the front of the queue then wake it
 43                  * up */
 44                 front = list_entry(vnode->writebacks.next,
 45                                    struct afs_writeback, link);
 46                 if (front->state == AFS_WBACK_SYNCING) {
 47                         _debug("wake up sync");
 48                         front->state = AFS_WBACK_COMPLETE;
 49                         wake_up(&front->waitq);
 50                 }
 51         }
 52 }
 53 
 54 /*
 55  * free a writeback record
 56  */
 57 static void afs_free_writeback(struct afs_writeback *wb)
 58 {
 59         _enter("");
 60         key_put(wb->key);
 61         kfree(wb);
 62 }
 63 
 64 /*
 65  * dispose of a reference to a writeback record
 66  */
 67 void afs_put_writeback(struct afs_writeback *wb)
 68 {
 69         struct afs_vnode *vnode = wb->vnode;
 70 
 71         _enter("{%d}", wb->usage);
 72 
 73         spin_lock(&vnode->writeback_lock);
 74         if (--wb->usage == 0)
 75                 afs_unlink_writeback(wb);
 76         else
 77                 wb = NULL;
 78         spin_unlock(&vnode->writeback_lock);
 79         if (wb)
 80                 afs_free_writeback(wb);
 81 }
 82 
 83 /*
 84  * partly or wholly fill a page that's under preparation for writing
 85  */
 86 static int afs_fill_page(struct afs_vnode *vnode, struct key *key,
 87                          loff_t pos, struct page *page)
 88 {
 89         loff_t i_size;
 90         int ret;
 91         int len;
 92 
 93         _enter(",,%llu", (unsigned long long)pos);
 94 
 95         i_size = i_size_read(&vnode->vfs_inode);
 96         if (pos + PAGE_CACHE_SIZE > i_size)
 97                 len = i_size - pos;
 98         else
 99                 len = PAGE_CACHE_SIZE;
100 
101         ret = afs_vnode_fetch_data(vnode, key, pos, len, page);
102         if (ret < 0) {
103                 if (ret == -ENOENT) {
104                         _debug("got NOENT from server"
105                                " - marking file deleted and stale");
106                         set_bit(AFS_VNODE_DELETED, &vnode->flags);
107                         ret = -ESTALE;
108                 }
109         }
110 
111         _leave(" = %d", ret);
112         return ret;
113 }
114 
115 /*
116  * prepare to perform part of a write to a page
117  */
118 int afs_write_begin(struct file *file, struct address_space *mapping,
119                     loff_t pos, unsigned len, unsigned flags,
120                     struct page **pagep, void **fsdata)
121 {
122         struct afs_writeback *candidate, *wb;
123         struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
124         struct page *page;
125         struct key *key = file->private_data;
126         unsigned from = pos & (PAGE_CACHE_SIZE - 1);
127         unsigned to = from + len;
128         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
129         int ret;
130 
131         _enter("{%x:%u},{%lx},%u,%u",
132                vnode->fid.vid, vnode->fid.vnode, index, from, to);
133 
134         candidate = kzalloc(sizeof(*candidate), GFP_KERNEL);
135         if (!candidate)
136                 return -ENOMEM;
137         candidate->vnode = vnode;
138         candidate->first = candidate->last = index;
139         candidate->offset_first = from;
140         candidate->to_last = to;
141         INIT_LIST_HEAD(&candidate->link);
142         candidate->usage = 1;
143         candidate->state = AFS_WBACK_PENDING;
144         init_waitqueue_head(&candidate->waitq);
145 
146         page = grab_cache_page_write_begin(mapping, index, flags);
147         if (!page) {
148                 kfree(candidate);
149                 return -ENOMEM;
150         }
151         *pagep = page;
152         /* page won't leak in error case: it eventually gets cleaned off LRU */
153 
154         if (!PageUptodate(page) && len != PAGE_CACHE_SIZE) {
155                 ret = afs_fill_page(vnode, key, index << PAGE_CACHE_SHIFT, page);
156                 if (ret < 0) {
157                         kfree(candidate);
158                         _leave(" = %d [prep]", ret);
159                         return ret;
160                 }
161                 SetPageUptodate(page);
162         }
163 
164 try_again:
165         spin_lock(&vnode->writeback_lock);
166 
167         /* see if this page is already pending a writeback under a suitable key
168          * - if so we can just join onto that one */
169         wb = (struct afs_writeback *) page_private(page);
170         if (wb) {
171                 if (wb->key == key && wb->state == AFS_WBACK_PENDING)
172                         goto subsume_in_current_wb;
173                 goto flush_conflicting_wb;
174         }
175 
176         if (index > 0) {
177                 /* see if we can find an already pending writeback that we can
178                  * append this page to */
179                 list_for_each_entry(wb, &vnode->writebacks, link) {
180                         if (wb->last == index - 1 && wb->key == key &&
181                             wb->state == AFS_WBACK_PENDING)
182                                 goto append_to_previous_wb;
183                 }
184         }
185 
186         list_add_tail(&candidate->link, &vnode->writebacks);
187         candidate->key = key_get(key);
188         spin_unlock(&vnode->writeback_lock);
189         SetPagePrivate(page);
190         set_page_private(page, (unsigned long) candidate);
191         _leave(" = 0 [new]");
192         return 0;
193 
194 subsume_in_current_wb:
195         _debug("subsume");
196         ASSERTRANGE(wb->first, <=, index, <=, wb->last);
197         if (index == wb->first && from < wb->offset_first)
198                 wb->offset_first = from;
199         if (index == wb->last && to > wb->to_last)
200                 wb->to_last = to;
201         spin_unlock(&vnode->writeback_lock);
202         kfree(candidate);
203         _leave(" = 0 [sub]");
204         return 0;
205 
206 append_to_previous_wb:
207         _debug("append into %lx-%lx", wb->first, wb->last);
208         wb->usage++;
209         wb->last++;
210         wb->to_last = to;
211         spin_unlock(&vnode->writeback_lock);
212         SetPagePrivate(page);
213         set_page_private(page, (unsigned long) wb);
214         kfree(candidate);
215         _leave(" = 0 [app]");
216         return 0;
217 
218         /* the page is currently bound to another context, so if it's dirty we
219          * need to flush it before we can use the new context */
220 flush_conflicting_wb:
221         _debug("flush conflict");
222         if (wb->state == AFS_WBACK_PENDING)
223                 wb->state = AFS_WBACK_CONFLICTING;
224         spin_unlock(&vnode->writeback_lock);
225         if (PageDirty(page)) {
226                 ret = afs_write_back_from_locked_page(wb, page);
227                 if (ret < 0) {
228                         afs_put_writeback(candidate);
229                         _leave(" = %d", ret);
230                         return ret;
231                 }
232         }
233 
234         /* the page holds a ref on the writeback record */
235         afs_put_writeback(wb);
236         set_page_private(page, 0);
237         ClearPagePrivate(page);
238         goto try_again;
239 }
240 
241 /*
242  * finalise part of a write to a page
243  */
244 int afs_write_end(struct file *file, struct address_space *mapping,
245                   loff_t pos, unsigned len, unsigned copied,
246                   struct page *page, void *fsdata)
247 {
248         struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
249         loff_t i_size, maybe_i_size;
250 
251         _enter("{%x:%u},{%lx}",
252                vnode->fid.vid, vnode->fid.vnode, page->index);
253 
254         maybe_i_size = pos + copied;
255 
256         i_size = i_size_read(&vnode->vfs_inode);
257         if (maybe_i_size > i_size) {
258                 spin_lock(&vnode->writeback_lock);
259                 i_size = i_size_read(&vnode->vfs_inode);
260                 if (maybe_i_size > i_size)
261                         i_size_write(&vnode->vfs_inode, maybe_i_size);
262                 spin_unlock(&vnode->writeback_lock);
263         }
264 
265         set_page_dirty(page);
266         if (PageDirty(page))
267                 _debug("dirtied");
268         unlock_page(page);
269         page_cache_release(page);
270 
271         return copied;
272 }
273 
274 /*
275  * kill all the pages in the given range
276  */
277 static void afs_kill_pages(struct afs_vnode *vnode, bool error,
278                            pgoff_t first, pgoff_t last)
279 {
280         struct pagevec pv;
281         unsigned count, loop;
282 
283         _enter("{%x:%u},%lx-%lx",
284                vnode->fid.vid, vnode->fid.vnode, first, last);
285 
286         pagevec_init(&pv, 0);
287 
288         do {
289                 _debug("kill %lx-%lx", first, last);
290 
291                 count = last - first + 1;
292                 if (count > PAGEVEC_SIZE)
293                         count = PAGEVEC_SIZE;
294                 pv.nr = find_get_pages_contig(vnode->vfs_inode.i_mapping,
295                                               first, count, pv.pages);
296                 ASSERTCMP(pv.nr, ==, count);
297 
298                 for (loop = 0; loop < count; loop++) {
299                         ClearPageUptodate(pv.pages[loop]);
300                         if (error)
301                                 SetPageError(pv.pages[loop]);
302                         end_page_writeback(pv.pages[loop]);
303                 }
304 
305                 __pagevec_release(&pv);
306         } while (first < last);
307 
308         _leave("");
309 }
310 
311 /*
312  * synchronously write back the locked page and any subsequent non-locked dirty
313  * pages also covered by the same writeback record
314  */
315 static int afs_write_back_from_locked_page(struct afs_writeback *wb,
316                                            struct page *primary_page)
317 {
318         struct page *pages[8], *page;
319         unsigned long count;
320         unsigned n, offset, to;
321         pgoff_t start, first, last;
322         int loop, ret;
323 
324         _enter(",%lx", primary_page->index);
325 
326         count = 1;
327         if (!clear_page_dirty_for_io(primary_page))
328                 BUG();
329         if (test_set_page_writeback(primary_page))
330                 BUG();
331 
332         /* find all consecutive lockable dirty pages, stopping when we find a
333          * page that is not immediately lockable, is not dirty or is missing,
334          * or we reach the end of the range */
335         start = primary_page->index;
336         if (start >= wb->last)
337                 goto no_more;
338         start++;
339         do {
340                 _debug("more %lx [%lx]", start, count);
341                 n = wb->last - start + 1;
342                 if (n > ARRAY_SIZE(pages))
343                         n = ARRAY_SIZE(pages);
344                 n = find_get_pages_contig(wb->vnode->vfs_inode.i_mapping,
345                                           start, n, pages);
346                 _debug("fgpc %u", n);
347                 if (n == 0)
348                         goto no_more;
349                 if (pages[0]->index != start) {
350                         do {
351                                 put_page(pages[--n]);
352                         } while (n > 0);
353                         goto no_more;
354                 }
355 
356                 for (loop = 0; loop < n; loop++) {
357                         page = pages[loop];
358                         if (page->index > wb->last)
359                                 break;
360                         if (!trylock_page(page))
361                                 break;
362                         if (!PageDirty(page) ||
363                             page_private(page) != (unsigned long) wb) {
364                                 unlock_page(page);
365                                 break;
366                         }
367                         if (!clear_page_dirty_for_io(page))
368                                 BUG();
369                         if (test_set_page_writeback(page))
370                                 BUG();
371                         unlock_page(page);
372                         put_page(page);
373                 }
374                 count += loop;
375                 if (loop < n) {
376                         for (; loop < n; loop++)
377                                 put_page(pages[loop]);
378                         goto no_more;
379                 }
380 
381                 start += loop;
382         } while (start <= wb->last && count < 65536);
383 
384 no_more:
385         /* we now have a contiguous set of dirty pages, each with writeback set
386          * and the dirty mark cleared; the first page is locked and must remain
387          * so, all the rest are unlocked */
388         first = primary_page->index;
389         last = first + count - 1;
390 
391         offset = (first == wb->first) ? wb->offset_first : 0;
392         to = (last == wb->last) ? wb->to_last : PAGE_SIZE;
393 
394         _debug("write back %lx[%u..] to %lx[..%u]", first, offset, last, to);
395 
396         ret = afs_vnode_store_data(wb, first, last, offset, to);
397         if (ret < 0) {
398                 switch (ret) {
399                 case -EDQUOT:
400                 case -ENOSPC:
401                         set_bit(AS_ENOSPC,
402                                 &wb->vnode->vfs_inode.i_mapping->flags);
403                         break;
404                 case -EROFS:
405                 case -EIO:
406                 case -EREMOTEIO:
407                 case -EFBIG:
408                 case -ENOENT:
409                 case -ENOMEDIUM:
410                 case -ENXIO:
411                         afs_kill_pages(wb->vnode, true, first, last);
412                         set_bit(AS_EIO, &wb->vnode->vfs_inode.i_mapping->flags);
413                         break;
414                 case -EACCES:
415                 case -EPERM:
416                 case -ENOKEY:
417                 case -EKEYEXPIRED:
418                 case -EKEYREJECTED:
419                 case -EKEYREVOKED:
420                         afs_kill_pages(wb->vnode, false, first, last);
421                         break;
422                 default:
423                         break;
424                 }
425         } else {
426                 ret = count;
427         }
428 
429         _leave(" = %d", ret);
430         return ret;
431 }
432 
433 /*
434  * write a page back to the server
435  * - the caller locked the page for us
436  */
437 int afs_writepage(struct page *page, struct writeback_control *wbc)
438 {
439         struct afs_writeback *wb;
440         int ret;
441 
442         _enter("{%lx},", page->index);
443 
444         wb = (struct afs_writeback *) page_private(page);
445         ASSERT(wb != NULL);
446 
447         ret = afs_write_back_from_locked_page(wb, page);
448         unlock_page(page);
449         if (ret < 0) {
450                 _leave(" = %d", ret);
451                 return 0;
452         }
453 
454         wbc->nr_to_write -= ret;
455 
456         _leave(" = 0");
457         return 0;
458 }
459 
460 /*
461  * write a region of pages back to the server
462  */
463 static int afs_writepages_region(struct address_space *mapping,
464                                  struct writeback_control *wbc,
465                                  pgoff_t index, pgoff_t end, pgoff_t *_next)
466 {
467         struct afs_writeback *wb;
468         struct page *page;
469         int ret, n;
470 
471         _enter(",,%lx,%lx,", index, end);
472 
473         do {
474                 n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
475                                        1, &page);
476                 if (!n)
477                         break;
478 
479                 _debug("wback %lx", page->index);
480 
481                 if (page->index > end) {
482                         *_next = index;
483                         page_cache_release(page);
484                         _leave(" = 0 [%lx]", *_next);
485                         return 0;
486                 }
487 
488                 /* at this point we hold neither mapping->tree_lock nor lock on
489                  * the page itself: the page may be truncated or invalidated
490                  * (changing page->mapping to NULL), or even swizzled back from
491                  * swapper_space to tmpfs file mapping
492                  */
493                 lock_page(page);
494 
495                 if (page->mapping != mapping) {
496                         unlock_page(page);
497                         page_cache_release(page);
498                         continue;
499                 }
500 
501                 if (wbc->sync_mode != WB_SYNC_NONE)
502                         wait_on_page_writeback(page);
503 
504                 if (PageWriteback(page) || !PageDirty(page)) {
505                         unlock_page(page);
506                         continue;
507                 }
508 
509                 wb = (struct afs_writeback *) page_private(page);
510                 ASSERT(wb != NULL);
511 
512                 spin_lock(&wb->vnode->writeback_lock);
513                 wb->state = AFS_WBACK_WRITING;
514                 spin_unlock(&wb->vnode->writeback_lock);
515 
516                 ret = afs_write_back_from_locked_page(wb, page);
517                 unlock_page(page);
518                 page_cache_release(page);
519                 if (ret < 0) {
520                         _leave(" = %d", ret);
521                         return ret;
522                 }
523 
524                 wbc->nr_to_write -= ret;
525 
526                 cond_resched();
527         } while (index < end && wbc->nr_to_write > 0);
528 
529         *_next = index;
530         _leave(" = 0 [%lx]", *_next);
531         return 0;
532 }
533 
534 /*
535  * write some of the pending data back to the server
536  */
537 int afs_writepages(struct address_space *mapping,
538                    struct writeback_control *wbc)
539 {
540         pgoff_t start, end, next;
541         int ret;
542 
543         _enter("");
544 
545         if (wbc->range_cyclic) {
546                 start = mapping->writeback_index;
547                 end = -1;
548                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
549                 if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
550                         ret = afs_writepages_region(mapping, wbc, 0, start,
551                                                     &next);
552                 mapping->writeback_index = next;
553         } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
554                 end = (pgoff_t)(LLONG_MAX >> PAGE_CACHE_SHIFT);
555                 ret = afs_writepages_region(mapping, wbc, 0, end, &next);
556                 if (wbc->nr_to_write > 0)
557                         mapping->writeback_index = next;
558         } else {
559                 start = wbc->range_start >> PAGE_CACHE_SHIFT;
560                 end = wbc->range_end >> PAGE_CACHE_SHIFT;
561                 ret = afs_writepages_region(mapping, wbc, start, end, &next);
562         }
563 
564         _leave(" = %d", ret);
565         return ret;
566 }
567 
568 /*
569  * completion of write to server
570  */
571 void afs_pages_written_back(struct afs_vnode *vnode, struct afs_call *call)
572 {
573         struct afs_writeback *wb = call->wb;
574         struct pagevec pv;
575         unsigned count, loop;
576         pgoff_t first = call->first, last = call->last;
577         bool free_wb;
578 
579         _enter("{%x:%u},{%lx-%lx}",
580                vnode->fid.vid, vnode->fid.vnode, first, last);
581 
582         ASSERT(wb != NULL);
583 
584         pagevec_init(&pv, 0);
585 
586         do {
587                 _debug("done %lx-%lx", first, last);
588 
589                 count = last - first + 1;
590                 if (count > PAGEVEC_SIZE)
591                         count = PAGEVEC_SIZE;
592                 pv.nr = find_get_pages_contig(call->mapping, first, count,
593                                               pv.pages);
594                 ASSERTCMP(pv.nr, ==, count);
595 
596                 spin_lock(&vnode->writeback_lock);
597                 for (loop = 0; loop < count; loop++) {
598                         struct page *page = pv.pages[loop];
599                         end_page_writeback(page);
600                         if (page_private(page) == (unsigned long) wb) {
601                                 set_page_private(page, 0);
602                                 ClearPagePrivate(page);
603                                 wb->usage--;
604                         }
605                 }
606                 free_wb = false;
607                 if (wb->usage == 0) {
608                         afs_unlink_writeback(wb);
609                         free_wb = true;
610                 }
611                 spin_unlock(&vnode->writeback_lock);
612                 first += count;
613                 if (free_wb) {
614                         afs_free_writeback(wb);
615                         wb = NULL;
616                 }
617 
618                 __pagevec_release(&pv);
619         } while (first <= last);
620 
621         _leave("");
622 }
623 
624 /*
625  * write to an AFS file
626  */
627 ssize_t afs_file_write(struct kiocb *iocb, struct iov_iter *from)
628 {
629         struct afs_vnode *vnode = AFS_FS_I(file_inode(iocb->ki_filp));
630         ssize_t result;
631         size_t count = iov_iter_count(from);
632 
633         _enter("{%x.%u},{%zu},",
634                vnode->fid.vid, vnode->fid.vnode, count);
635 
636         if (IS_SWAPFILE(&vnode->vfs_inode)) {
637                 printk(KERN_INFO
638                        "AFS: Attempt to write to active swap file!\n");
639                 return -EBUSY;
640         }
641 
642         if (!count)
643                 return 0;
644 
645         result = generic_file_write_iter(iocb, from);
646         if (IS_ERR_VALUE(result)) {
647                 _leave(" = %zd", result);
648                 return result;
649         }
650 
651         _leave(" = %zd", result);
652         return result;
653 }
654 
655 /*
656  * flush the vnode to the fileserver
657  */
658 int afs_writeback_all(struct afs_vnode *vnode)
659 {
660         struct address_space *mapping = vnode->vfs_inode.i_mapping;
661         struct writeback_control wbc = {
662                 .sync_mode      = WB_SYNC_ALL,
663                 .nr_to_write    = LONG_MAX,
664                 .range_cyclic   = 1,
665         };
666         int ret;
667 
668         _enter("");
669 
670         ret = mapping->a_ops->writepages(mapping, &wbc);
671         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
672 
673         _leave(" = %d", ret);
674         return ret;
675 }
676 
677 /*
678  * flush any dirty pages for this process, and check for write errors.
679  * - the return status from this call provides a reliable indication of
680  *   whether any write errors occurred for this process.
681  */
682 int afs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
683 {
684         struct inode *inode = file_inode(file);
685         struct afs_writeback *wb, *xwb;
686         struct afs_vnode *vnode = AFS_FS_I(inode);
687         int ret;
688 
689         _enter("{%x:%u},{n=%pD},%d",
690                vnode->fid.vid, vnode->fid.vnode, file,
691                datasync);
692 
693         ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
694         if (ret)
695                 return ret;
696         mutex_lock(&inode->i_mutex);
697 
698         /* use a writeback record as a marker in the queue - when this reaches
699          * the front of the queue, all the outstanding writes are either
700          * completed or rejected */
701         wb = kzalloc(sizeof(*wb), GFP_KERNEL);
702         if (!wb) {
703                 ret = -ENOMEM;
704                 goto out;
705         }
706         wb->vnode = vnode;
707         wb->first = 0;
708         wb->last = -1;
709         wb->offset_first = 0;
710         wb->to_last = PAGE_SIZE;
711         wb->usage = 1;
712         wb->state = AFS_WBACK_SYNCING;
713         init_waitqueue_head(&wb->waitq);
714 
715         spin_lock(&vnode->writeback_lock);
716         list_for_each_entry(xwb, &vnode->writebacks, link) {
717                 if (xwb->state == AFS_WBACK_PENDING)
718                         xwb->state = AFS_WBACK_CONFLICTING;
719         }
720         list_add_tail(&wb->link, &vnode->writebacks);
721         spin_unlock(&vnode->writeback_lock);
722 
723         /* push all the outstanding writebacks to the server */
724         ret = afs_writeback_all(vnode);
725         if (ret < 0) {
726                 afs_put_writeback(wb);
727                 _leave(" = %d [wb]", ret);
728                 goto out;
729         }
730 
731         /* wait for the preceding writes to actually complete */
732         ret = wait_event_interruptible(wb->waitq,
733                                        wb->state == AFS_WBACK_COMPLETE ||
734                                        vnode->writebacks.next == &wb->link);
735         afs_put_writeback(wb);
736         _leave(" = %d", ret);
737 out:
738         mutex_unlock(&inode->i_mutex);
739         return ret;
740 }
741 
742 /*
743  * notification that a previously read-only page is about to become writable
744  * - if it returns an error, the caller will deliver a bus error signal
745  */
746 int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
747 {
748         struct afs_vnode *vnode = AFS_FS_I(vma->vm_file->f_mapping->host);
749 
750         _enter("{{%x:%u}},{%lx}",
751                vnode->fid.vid, vnode->fid.vnode, page->index);
752 
753         /* wait for the page to be written to the cache before we allow it to
754          * be modified */
755 #ifdef CONFIG_AFS_FSCACHE
756         fscache_wait_on_page_write(vnode->cache, page);
757 #endif
758 
759         _leave(" = 0");
760         return 0;
761 }
762 

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