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TOMOYO Linux Cross Reference
Linux/mm/backing-dev.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 
  3 #include <linux/wait.h>
  4 #include <linux/backing-dev.h>
  5 #include <linux/kthread.h>
  6 #include <linux/freezer.h>
  7 #include <linux/fs.h>
  8 #include <linux/pagemap.h>
  9 #include <linux/mm.h>
 10 #include <linux/sched.h>
 11 #include <linux/module.h>
 12 #include <linux/writeback.h>
 13 #include <linux/device.h>
 14 #include <trace/events/writeback.h>
 15 
 16 struct backing_dev_info noop_backing_dev_info = {
 17         .name           = "noop",
 18         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
 19 };
 20 EXPORT_SYMBOL_GPL(noop_backing_dev_info);
 21 
 22 static struct class *bdi_class;
 23 
 24 /*
 25  * bdi_lock protects updates to bdi_list. bdi_list has RCU reader side
 26  * locking.
 27  */
 28 DEFINE_SPINLOCK(bdi_lock);
 29 LIST_HEAD(bdi_list);
 30 
 31 /* bdi_wq serves all asynchronous writeback tasks */
 32 struct workqueue_struct *bdi_wq;
 33 
 34 #ifdef CONFIG_DEBUG_FS
 35 #include <linux/debugfs.h>
 36 #include <linux/seq_file.h>
 37 
 38 static struct dentry *bdi_debug_root;
 39 
 40 static void bdi_debug_init(void)
 41 {
 42         bdi_debug_root = debugfs_create_dir("bdi", NULL);
 43 }
 44 
 45 static int bdi_debug_stats_show(struct seq_file *m, void *v)
 46 {
 47         struct backing_dev_info *bdi = m->private;
 48         struct bdi_writeback *wb = &bdi->wb;
 49         unsigned long background_thresh;
 50         unsigned long dirty_thresh;
 51         unsigned long wb_thresh;
 52         unsigned long nr_dirty, nr_io, nr_more_io, nr_dirty_time;
 53         struct inode *inode;
 54 
 55         nr_dirty = nr_io = nr_more_io = nr_dirty_time = 0;
 56         spin_lock(&wb->list_lock);
 57         list_for_each_entry(inode, &wb->b_dirty, i_io_list)
 58                 nr_dirty++;
 59         list_for_each_entry(inode, &wb->b_io, i_io_list)
 60                 nr_io++;
 61         list_for_each_entry(inode, &wb->b_more_io, i_io_list)
 62                 nr_more_io++;
 63         list_for_each_entry(inode, &wb->b_dirty_time, i_io_list)
 64                 if (inode->i_state & I_DIRTY_TIME)
 65                         nr_dirty_time++;
 66         spin_unlock(&wb->list_lock);
 67 
 68         global_dirty_limits(&background_thresh, &dirty_thresh);
 69         wb_thresh = wb_calc_thresh(wb, dirty_thresh);
 70 
 71 #define K(x) ((x) << (PAGE_SHIFT - 10))
 72         seq_printf(m,
 73                    "BdiWriteback:       %10lu kB\n"
 74                    "BdiReclaimable:     %10lu kB\n"
 75                    "BdiDirtyThresh:     %10lu kB\n"
 76                    "DirtyThresh:        %10lu kB\n"
 77                    "BackgroundThresh:   %10lu kB\n"
 78                    "BdiDirtied:         %10lu kB\n"
 79                    "BdiWritten:         %10lu kB\n"
 80                    "BdiWriteBandwidth:  %10lu kBps\n"
 81                    "b_dirty:            %10lu\n"
 82                    "b_io:               %10lu\n"
 83                    "b_more_io:          %10lu\n"
 84                    "b_dirty_time:       %10lu\n"
 85                    "bdi_list:           %10u\n"
 86                    "state:              %10lx\n",
 87                    (unsigned long) K(wb_stat(wb, WB_WRITEBACK)),
 88                    (unsigned long) K(wb_stat(wb, WB_RECLAIMABLE)),
 89                    K(wb_thresh),
 90                    K(dirty_thresh),
 91                    K(background_thresh),
 92                    (unsigned long) K(wb_stat(wb, WB_DIRTIED)),
 93                    (unsigned long) K(wb_stat(wb, WB_WRITTEN)),
 94                    (unsigned long) K(wb->write_bandwidth),
 95                    nr_dirty,
 96                    nr_io,
 97                    nr_more_io,
 98                    nr_dirty_time,
 99                    !list_empty(&bdi->bdi_list), bdi->wb.state);
100 #undef K
101 
102         return 0;
103 }
104 DEFINE_SHOW_ATTRIBUTE(bdi_debug_stats);
105 
106 static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
107 {
108         bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
109 
110         debugfs_create_file("stats", 0444, bdi->debug_dir, bdi,
111                             &bdi_debug_stats_fops);
112 }
113 
114 static void bdi_debug_unregister(struct backing_dev_info *bdi)
115 {
116         debugfs_remove_recursive(bdi->debug_dir);
117 }
118 #else
119 static inline void bdi_debug_init(void)
120 {
121 }
122 static inline void bdi_debug_register(struct backing_dev_info *bdi,
123                                       const char *name)
124 {
125 }
126 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
127 {
128 }
129 #endif
130 
131 static ssize_t read_ahead_kb_store(struct device *dev,
132                                   struct device_attribute *attr,
133                                   const char *buf, size_t count)
134 {
135         struct backing_dev_info *bdi = dev_get_drvdata(dev);
136         unsigned long read_ahead_kb;
137         ssize_t ret;
138 
139         ret = kstrtoul(buf, 10, &read_ahead_kb);
140         if (ret < 0)
141                 return ret;
142 
143         bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
144 
145         return count;
146 }
147 
148 #define K(pages) ((pages) << (PAGE_SHIFT - 10))
149 
150 #define BDI_SHOW(name, expr)                                            \
151 static ssize_t name##_show(struct device *dev,                          \
152                            struct device_attribute *attr, char *page)   \
153 {                                                                       \
154         struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
155                                                                         \
156         return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
157 }                                                                       \
158 static DEVICE_ATTR_RW(name);
159 
160 BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
161 
162 static ssize_t min_ratio_store(struct device *dev,
163                 struct device_attribute *attr, const char *buf, size_t count)
164 {
165         struct backing_dev_info *bdi = dev_get_drvdata(dev);
166         unsigned int ratio;
167         ssize_t ret;
168 
169         ret = kstrtouint(buf, 10, &ratio);
170         if (ret < 0)
171                 return ret;
172 
173         ret = bdi_set_min_ratio(bdi, ratio);
174         if (!ret)
175                 ret = count;
176 
177         return ret;
178 }
179 BDI_SHOW(min_ratio, bdi->min_ratio)
180 
181 static ssize_t max_ratio_store(struct device *dev,
182                 struct device_attribute *attr, const char *buf, size_t count)
183 {
184         struct backing_dev_info *bdi = dev_get_drvdata(dev);
185         unsigned int ratio;
186         ssize_t ret;
187 
188         ret = kstrtouint(buf, 10, &ratio);
189         if (ret < 0)
190                 return ret;
191 
192         ret = bdi_set_max_ratio(bdi, ratio);
193         if (!ret)
194                 ret = count;
195 
196         return ret;
197 }
198 BDI_SHOW(max_ratio, bdi->max_ratio)
199 
200 static ssize_t stable_pages_required_show(struct device *dev,
201                                           struct device_attribute *attr,
202                                           char *page)
203 {
204         struct backing_dev_info *bdi = dev_get_drvdata(dev);
205 
206         return snprintf(page, PAGE_SIZE-1, "%d\n",
207                         bdi_cap_stable_pages_required(bdi) ? 1 : 0);
208 }
209 static DEVICE_ATTR_RO(stable_pages_required);
210 
211 static struct attribute *bdi_dev_attrs[] = {
212         &dev_attr_read_ahead_kb.attr,
213         &dev_attr_min_ratio.attr,
214         &dev_attr_max_ratio.attr,
215         &dev_attr_stable_pages_required.attr,
216         NULL,
217 };
218 ATTRIBUTE_GROUPS(bdi_dev);
219 
220 static __init int bdi_class_init(void)
221 {
222         bdi_class = class_create(THIS_MODULE, "bdi");
223         if (IS_ERR(bdi_class))
224                 return PTR_ERR(bdi_class);
225 
226         bdi_class->dev_groups = bdi_dev_groups;
227         bdi_debug_init();
228 
229         return 0;
230 }
231 postcore_initcall(bdi_class_init);
232 
233 static int bdi_init(struct backing_dev_info *bdi);
234 
235 static int __init default_bdi_init(void)
236 {
237         int err;
238 
239         bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE |
240                                               WQ_UNBOUND | WQ_SYSFS, 0);
241         if (!bdi_wq)
242                 return -ENOMEM;
243 
244         err = bdi_init(&noop_backing_dev_info);
245 
246         return err;
247 }
248 subsys_initcall(default_bdi_init);
249 
250 /*
251  * This function is used when the first inode for this wb is marked dirty. It
252  * wakes-up the corresponding bdi thread which should then take care of the
253  * periodic background write-out of dirty inodes. Since the write-out would
254  * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
255  * set up a timer which wakes the bdi thread up later.
256  *
257  * Note, we wouldn't bother setting up the timer, but this function is on the
258  * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
259  * by delaying the wake-up.
260  *
261  * We have to be careful not to postpone flush work if it is scheduled for
262  * earlier. Thus we use queue_delayed_work().
263  */
264 void wb_wakeup_delayed(struct bdi_writeback *wb)
265 {
266         unsigned long timeout;
267 
268         timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
269         spin_lock_bh(&wb->work_lock);
270         if (test_bit(WB_registered, &wb->state))
271                 queue_delayed_work(bdi_wq, &wb->dwork, timeout);
272         spin_unlock_bh(&wb->work_lock);
273 }
274 
275 /*
276  * Initial write bandwidth: 100 MB/s
277  */
278 #define INIT_BW         (100 << (20 - PAGE_SHIFT))
279 
280 static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
281                    int blkcg_id, gfp_t gfp)
282 {
283         int i, err;
284 
285         memset(wb, 0, sizeof(*wb));
286 
287         if (wb != &bdi->wb)
288                 bdi_get(bdi);
289         wb->bdi = bdi;
290         wb->last_old_flush = jiffies;
291         INIT_LIST_HEAD(&wb->b_dirty);
292         INIT_LIST_HEAD(&wb->b_io);
293         INIT_LIST_HEAD(&wb->b_more_io);
294         INIT_LIST_HEAD(&wb->b_dirty_time);
295         spin_lock_init(&wb->list_lock);
296 
297         wb->bw_time_stamp = jiffies;
298         wb->balanced_dirty_ratelimit = INIT_BW;
299         wb->dirty_ratelimit = INIT_BW;
300         wb->write_bandwidth = INIT_BW;
301         wb->avg_write_bandwidth = INIT_BW;
302 
303         spin_lock_init(&wb->work_lock);
304         INIT_LIST_HEAD(&wb->work_list);
305         INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
306         wb->dirty_sleep = jiffies;
307 
308         wb->congested = wb_congested_get_create(bdi, blkcg_id, gfp);
309         if (!wb->congested) {
310                 err = -ENOMEM;
311                 goto out_put_bdi;
312         }
313 
314         err = fprop_local_init_percpu(&wb->completions, gfp);
315         if (err)
316                 goto out_put_cong;
317 
318         for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
319                 err = percpu_counter_init(&wb->stat[i], 0, gfp);
320                 if (err)
321                         goto out_destroy_stat;
322         }
323 
324         return 0;
325 
326 out_destroy_stat:
327         while (i--)
328                 percpu_counter_destroy(&wb->stat[i]);
329         fprop_local_destroy_percpu(&wb->completions);
330 out_put_cong:
331         wb_congested_put(wb->congested);
332 out_put_bdi:
333         if (wb != &bdi->wb)
334                 bdi_put(bdi);
335         return err;
336 }
337 
338 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb);
339 
340 /*
341  * Remove bdi from the global list and shutdown any threads we have running
342  */
343 static void wb_shutdown(struct bdi_writeback *wb)
344 {
345         /* Make sure nobody queues further work */
346         spin_lock_bh(&wb->work_lock);
347         if (!test_and_clear_bit(WB_registered, &wb->state)) {
348                 spin_unlock_bh(&wb->work_lock);
349                 return;
350         }
351         spin_unlock_bh(&wb->work_lock);
352 
353         cgwb_remove_from_bdi_list(wb);
354         /*
355          * Drain work list and shutdown the delayed_work.  !WB_registered
356          * tells wb_workfn() that @wb is dying and its work_list needs to
357          * be drained no matter what.
358          */
359         mod_delayed_work(bdi_wq, &wb->dwork, 0);
360         flush_delayed_work(&wb->dwork);
361         WARN_ON(!list_empty(&wb->work_list));
362 }
363 
364 static void wb_exit(struct bdi_writeback *wb)
365 {
366         int i;
367 
368         WARN_ON(delayed_work_pending(&wb->dwork));
369 
370         for (i = 0; i < NR_WB_STAT_ITEMS; i++)
371                 percpu_counter_destroy(&wb->stat[i]);
372 
373         fprop_local_destroy_percpu(&wb->completions);
374         wb_congested_put(wb->congested);
375         if (wb != &wb->bdi->wb)
376                 bdi_put(wb->bdi);
377 }
378 
379 #ifdef CONFIG_CGROUP_WRITEBACK
380 
381 #include <linux/memcontrol.h>
382 
383 /*
384  * cgwb_lock protects bdi->cgwb_tree, bdi->cgwb_congested_tree,
385  * blkcg->cgwb_list, and memcg->cgwb_list.  bdi->cgwb_tree is also RCU
386  * protected.
387  */
388 static DEFINE_SPINLOCK(cgwb_lock);
389 static struct workqueue_struct *cgwb_release_wq;
390 
391 /**
392  * wb_congested_get_create - get or create a wb_congested
393  * @bdi: associated bdi
394  * @blkcg_id: ID of the associated blkcg
395  * @gfp: allocation mask
396  *
397  * Look up the wb_congested for @blkcg_id on @bdi.  If missing, create one.
398  * The returned wb_congested has its reference count incremented.  Returns
399  * NULL on failure.
400  */
401 struct bdi_writeback_congested *
402 wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
403 {
404         struct bdi_writeback_congested *new_congested = NULL, *congested;
405         struct rb_node **node, *parent;
406         unsigned long flags;
407 retry:
408         spin_lock_irqsave(&cgwb_lock, flags);
409 
410         node = &bdi->cgwb_congested_tree.rb_node;
411         parent = NULL;
412 
413         while (*node != NULL) {
414                 parent = *node;
415                 congested = rb_entry(parent, struct bdi_writeback_congested,
416                                      rb_node);
417                 if (congested->blkcg_id < blkcg_id)
418                         node = &parent->rb_left;
419                 else if (congested->blkcg_id > blkcg_id)
420                         node = &parent->rb_right;
421                 else
422                         goto found;
423         }
424 
425         if (new_congested) {
426                 /* !found and storage for new one already allocated, insert */
427                 congested = new_congested;
428                 rb_link_node(&congested->rb_node, parent, node);
429                 rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
430                 spin_unlock_irqrestore(&cgwb_lock, flags);
431                 return congested;
432         }
433 
434         spin_unlock_irqrestore(&cgwb_lock, flags);
435 
436         /* allocate storage for new one and retry */
437         new_congested = kzalloc(sizeof(*new_congested), gfp);
438         if (!new_congested)
439                 return NULL;
440 
441         refcount_set(&new_congested->refcnt, 1);
442         new_congested->__bdi = bdi;
443         new_congested->blkcg_id = blkcg_id;
444         goto retry;
445 
446 found:
447         refcount_inc(&congested->refcnt);
448         spin_unlock_irqrestore(&cgwb_lock, flags);
449         kfree(new_congested);
450         return congested;
451 }
452 
453 /**
454  * wb_congested_put - put a wb_congested
455  * @congested: wb_congested to put
456  *
457  * Put @congested and destroy it if the refcnt reaches zero.
458  */
459 void wb_congested_put(struct bdi_writeback_congested *congested)
460 {
461         unsigned long flags;
462 
463         if (!refcount_dec_and_lock_irqsave(&congested->refcnt, &cgwb_lock, &flags))
464                 return;
465 
466         /* bdi might already have been destroyed leaving @congested unlinked */
467         if (congested->__bdi) {
468                 rb_erase(&congested->rb_node,
469                          &congested->__bdi->cgwb_congested_tree);
470                 congested->__bdi = NULL;
471         }
472 
473         spin_unlock_irqrestore(&cgwb_lock, flags);
474         kfree(congested);
475 }
476 
477 static void cgwb_release_workfn(struct work_struct *work)
478 {
479         struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
480                                                 release_work);
481         struct blkcg *blkcg = css_to_blkcg(wb->blkcg_css);
482 
483         mutex_lock(&wb->bdi->cgwb_release_mutex);
484         wb_shutdown(wb);
485 
486         css_put(wb->memcg_css);
487         css_put(wb->blkcg_css);
488         mutex_unlock(&wb->bdi->cgwb_release_mutex);
489 
490         /* triggers blkg destruction if cgwb_refcnt becomes zero */
491         blkcg_cgwb_put(blkcg);
492 
493         fprop_local_destroy_percpu(&wb->memcg_completions);
494         percpu_ref_exit(&wb->refcnt);
495         wb_exit(wb);
496         kfree_rcu(wb, rcu);
497 }
498 
499 static void cgwb_release(struct percpu_ref *refcnt)
500 {
501         struct bdi_writeback *wb = container_of(refcnt, struct bdi_writeback,
502                                                 refcnt);
503         queue_work(cgwb_release_wq, &wb->release_work);
504 }
505 
506 static void cgwb_kill(struct bdi_writeback *wb)
507 {
508         lockdep_assert_held(&cgwb_lock);
509 
510         WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id));
511         list_del(&wb->memcg_node);
512         list_del(&wb->blkcg_node);
513         percpu_ref_kill(&wb->refcnt);
514 }
515 
516 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
517 {
518         spin_lock_irq(&cgwb_lock);
519         list_del_rcu(&wb->bdi_node);
520         spin_unlock_irq(&cgwb_lock);
521 }
522 
523 static int cgwb_create(struct backing_dev_info *bdi,
524                        struct cgroup_subsys_state *memcg_css, gfp_t gfp)
525 {
526         struct mem_cgroup *memcg;
527         struct cgroup_subsys_state *blkcg_css;
528         struct blkcg *blkcg;
529         struct list_head *memcg_cgwb_list, *blkcg_cgwb_list;
530         struct bdi_writeback *wb;
531         unsigned long flags;
532         int ret = 0;
533 
534         memcg = mem_cgroup_from_css(memcg_css);
535         blkcg_css = cgroup_get_e_css(memcg_css->cgroup, &io_cgrp_subsys);
536         blkcg = css_to_blkcg(blkcg_css);
537         memcg_cgwb_list = &memcg->cgwb_list;
538         blkcg_cgwb_list = &blkcg->cgwb_list;
539 
540         /* look up again under lock and discard on blkcg mismatch */
541         spin_lock_irqsave(&cgwb_lock, flags);
542         wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
543         if (wb && wb->blkcg_css != blkcg_css) {
544                 cgwb_kill(wb);
545                 wb = NULL;
546         }
547         spin_unlock_irqrestore(&cgwb_lock, flags);
548         if (wb)
549                 goto out_put;
550 
551         /* need to create a new one */
552         wb = kmalloc(sizeof(*wb), gfp);
553         if (!wb) {
554                 ret = -ENOMEM;
555                 goto out_put;
556         }
557 
558         ret = wb_init(wb, bdi, blkcg_css->id, gfp);
559         if (ret)
560                 goto err_free;
561 
562         ret = percpu_ref_init(&wb->refcnt, cgwb_release, 0, gfp);
563         if (ret)
564                 goto err_wb_exit;
565 
566         ret = fprop_local_init_percpu(&wb->memcg_completions, gfp);
567         if (ret)
568                 goto err_ref_exit;
569 
570         wb->memcg_css = memcg_css;
571         wb->blkcg_css = blkcg_css;
572         INIT_WORK(&wb->release_work, cgwb_release_workfn);
573         set_bit(WB_registered, &wb->state);
574 
575         /*
576          * The root wb determines the registered state of the whole bdi and
577          * memcg_cgwb_list and blkcg_cgwb_list's next pointers indicate
578          * whether they're still online.  Don't link @wb if any is dead.
579          * See wb_memcg_offline() and wb_blkcg_offline().
580          */
581         ret = -ENODEV;
582         spin_lock_irqsave(&cgwb_lock, flags);
583         if (test_bit(WB_registered, &bdi->wb.state) &&
584             blkcg_cgwb_list->next && memcg_cgwb_list->next) {
585                 /* we might have raced another instance of this function */
586                 ret = radix_tree_insert(&bdi->cgwb_tree, memcg_css->id, wb);
587                 if (!ret) {
588                         list_add_tail_rcu(&wb->bdi_node, &bdi->wb_list);
589                         list_add(&wb->memcg_node, memcg_cgwb_list);
590                         list_add(&wb->blkcg_node, blkcg_cgwb_list);
591                         blkcg_cgwb_get(blkcg);
592                         css_get(memcg_css);
593                         css_get(blkcg_css);
594                 }
595         }
596         spin_unlock_irqrestore(&cgwb_lock, flags);
597         if (ret) {
598                 if (ret == -EEXIST)
599                         ret = 0;
600                 goto err_fprop_exit;
601         }
602         goto out_put;
603 
604 err_fprop_exit:
605         fprop_local_destroy_percpu(&wb->memcg_completions);
606 err_ref_exit:
607         percpu_ref_exit(&wb->refcnt);
608 err_wb_exit:
609         wb_exit(wb);
610 err_free:
611         kfree(wb);
612 out_put:
613         css_put(blkcg_css);
614         return ret;
615 }
616 
617 /**
618  * wb_get_create - get wb for a given memcg, create if necessary
619  * @bdi: target bdi
620  * @memcg_css: cgroup_subsys_state of the target memcg (must have positive ref)
621  * @gfp: allocation mask to use
622  *
623  * Try to get the wb for @memcg_css on @bdi.  If it doesn't exist, try to
624  * create one.  The returned wb has its refcount incremented.
625  *
626  * This function uses css_get() on @memcg_css and thus expects its refcnt
627  * to be positive on invocation.  IOW, rcu_read_lock() protection on
628  * @memcg_css isn't enough.  try_get it before calling this function.
629  *
630  * A wb is keyed by its associated memcg.  As blkcg implicitly enables
631  * memcg on the default hierarchy, memcg association is guaranteed to be
632  * more specific (equal or descendant to the associated blkcg) and thus can
633  * identify both the memcg and blkcg associations.
634  *
635  * Because the blkcg associated with a memcg may change as blkcg is enabled
636  * and disabled closer to root in the hierarchy, each wb keeps track of
637  * both the memcg and blkcg associated with it and verifies the blkcg on
638  * each lookup.  On mismatch, the existing wb is discarded and a new one is
639  * created.
640  */
641 struct bdi_writeback *wb_get_create(struct backing_dev_info *bdi,
642                                     struct cgroup_subsys_state *memcg_css,
643                                     gfp_t gfp)
644 {
645         struct bdi_writeback *wb;
646 
647         might_sleep_if(gfpflags_allow_blocking(gfp));
648 
649         if (!memcg_css->parent)
650                 return &bdi->wb;
651 
652         do {
653                 rcu_read_lock();
654                 wb = radix_tree_lookup(&bdi->cgwb_tree, memcg_css->id);
655                 if (wb) {
656                         struct cgroup_subsys_state *blkcg_css;
657 
658                         /* see whether the blkcg association has changed */
659                         blkcg_css = cgroup_get_e_css(memcg_css->cgroup,
660                                                      &io_cgrp_subsys);
661                         if (unlikely(wb->blkcg_css != blkcg_css ||
662                                      !wb_tryget(wb)))
663                                 wb = NULL;
664                         css_put(blkcg_css);
665                 }
666                 rcu_read_unlock();
667         } while (!wb && !cgwb_create(bdi, memcg_css, gfp));
668 
669         return wb;
670 }
671 
672 static int cgwb_bdi_init(struct backing_dev_info *bdi)
673 {
674         int ret;
675 
676         INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);
677         bdi->cgwb_congested_tree = RB_ROOT;
678         mutex_init(&bdi->cgwb_release_mutex);
679         init_rwsem(&bdi->wb_switch_rwsem);
680 
681         ret = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
682         if (!ret) {
683                 bdi->wb.memcg_css = &root_mem_cgroup->css;
684                 bdi->wb.blkcg_css = blkcg_root_css;
685         }
686         return ret;
687 }
688 
689 static void cgwb_bdi_unregister(struct backing_dev_info *bdi)
690 {
691         struct radix_tree_iter iter;
692         void **slot;
693         struct bdi_writeback *wb;
694 
695         WARN_ON(test_bit(WB_registered, &bdi->wb.state));
696 
697         spin_lock_irq(&cgwb_lock);
698         radix_tree_for_each_slot(slot, &bdi->cgwb_tree, &iter, 0)
699                 cgwb_kill(*slot);
700         spin_unlock_irq(&cgwb_lock);
701 
702         mutex_lock(&bdi->cgwb_release_mutex);
703         spin_lock_irq(&cgwb_lock);
704         while (!list_empty(&bdi->wb_list)) {
705                 wb = list_first_entry(&bdi->wb_list, struct bdi_writeback,
706                                       bdi_node);
707                 spin_unlock_irq(&cgwb_lock);
708                 wb_shutdown(wb);
709                 spin_lock_irq(&cgwb_lock);
710         }
711         spin_unlock_irq(&cgwb_lock);
712         mutex_unlock(&bdi->cgwb_release_mutex);
713 }
714 
715 /**
716  * wb_memcg_offline - kill all wb's associated with a memcg being offlined
717  * @memcg: memcg being offlined
718  *
719  * Also prevents creation of any new wb's associated with @memcg.
720  */
721 void wb_memcg_offline(struct mem_cgroup *memcg)
722 {
723         struct list_head *memcg_cgwb_list = &memcg->cgwb_list;
724         struct bdi_writeback *wb, *next;
725 
726         spin_lock_irq(&cgwb_lock);
727         list_for_each_entry_safe(wb, next, memcg_cgwb_list, memcg_node)
728                 cgwb_kill(wb);
729         memcg_cgwb_list->next = NULL;   /* prevent new wb's */
730         spin_unlock_irq(&cgwb_lock);
731 }
732 
733 /**
734  * wb_blkcg_offline - kill all wb's associated with a blkcg being offlined
735  * @blkcg: blkcg being offlined
736  *
737  * Also prevents creation of any new wb's associated with @blkcg.
738  */
739 void wb_blkcg_offline(struct blkcg *blkcg)
740 {
741         struct bdi_writeback *wb, *next;
742 
743         spin_lock_irq(&cgwb_lock);
744         list_for_each_entry_safe(wb, next, &blkcg->cgwb_list, blkcg_node)
745                 cgwb_kill(wb);
746         blkcg->cgwb_list.next = NULL;   /* prevent new wb's */
747         spin_unlock_irq(&cgwb_lock);
748 }
749 
750 static void cgwb_bdi_exit(struct backing_dev_info *bdi)
751 {
752         struct rb_node *rbn;
753 
754         spin_lock_irq(&cgwb_lock);
755         while ((rbn = rb_first(&bdi->cgwb_congested_tree))) {
756                 struct bdi_writeback_congested *congested =
757                         rb_entry(rbn, struct bdi_writeback_congested, rb_node);
758 
759                 rb_erase(rbn, &bdi->cgwb_congested_tree);
760                 congested->__bdi = NULL;        /* mark @congested unlinked */
761         }
762         spin_unlock_irq(&cgwb_lock);
763 }
764 
765 static void cgwb_bdi_register(struct backing_dev_info *bdi)
766 {
767         spin_lock_irq(&cgwb_lock);
768         list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
769         spin_unlock_irq(&cgwb_lock);
770 }
771 
772 static int __init cgwb_init(void)
773 {
774         /*
775          * There can be many concurrent release work items overwhelming
776          * system_wq.  Put them in a separate wq and limit concurrency.
777          * There's no point in executing many of these in parallel.
778          */
779         cgwb_release_wq = alloc_workqueue("cgwb_release", 0, 1);
780         if (!cgwb_release_wq)
781                 return -ENOMEM;
782 
783         return 0;
784 }
785 subsys_initcall(cgwb_init);
786 
787 #else   /* CONFIG_CGROUP_WRITEBACK */
788 
789 static int cgwb_bdi_init(struct backing_dev_info *bdi)
790 {
791         int err;
792 
793         bdi->wb_congested = kzalloc(sizeof(*bdi->wb_congested), GFP_KERNEL);
794         if (!bdi->wb_congested)
795                 return -ENOMEM;
796 
797         refcount_set(&bdi->wb_congested->refcnt, 1);
798 
799         err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
800         if (err) {
801                 wb_congested_put(bdi->wb_congested);
802                 return err;
803         }
804         return 0;
805 }
806 
807 static void cgwb_bdi_unregister(struct backing_dev_info *bdi) { }
808 
809 static void cgwb_bdi_exit(struct backing_dev_info *bdi)
810 {
811         wb_congested_put(bdi->wb_congested);
812 }
813 
814 static void cgwb_bdi_register(struct backing_dev_info *bdi)
815 {
816         list_add_tail_rcu(&bdi->wb.bdi_node, &bdi->wb_list);
817 }
818 
819 static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
820 {
821         list_del_rcu(&wb->bdi_node);
822 }
823 
824 #endif  /* CONFIG_CGROUP_WRITEBACK */
825 
826 static int bdi_init(struct backing_dev_info *bdi)
827 {
828         int ret;
829 
830         bdi->dev = NULL;
831 
832         kref_init(&bdi->refcnt);
833         bdi->min_ratio = 0;
834         bdi->max_ratio = 100;
835         bdi->max_prop_frac = FPROP_FRAC_BASE;
836         INIT_LIST_HEAD(&bdi->bdi_list);
837         INIT_LIST_HEAD(&bdi->wb_list);
838         init_waitqueue_head(&bdi->wb_waitq);
839 
840         ret = cgwb_bdi_init(bdi);
841 
842         return ret;
843 }
844 
845 struct backing_dev_info *bdi_alloc_node(gfp_t gfp_mask, int node_id)
846 {
847         struct backing_dev_info *bdi;
848 
849         bdi = kmalloc_node(sizeof(struct backing_dev_info),
850                            gfp_mask | __GFP_ZERO, node_id);
851         if (!bdi)
852                 return NULL;
853 
854         if (bdi_init(bdi)) {
855                 kfree(bdi);
856                 return NULL;
857         }
858         return bdi;
859 }
860 EXPORT_SYMBOL(bdi_alloc_node);
861 
862 int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
863 {
864         struct device *dev;
865 
866         if (bdi->dev)   /* The driver needs to use separate queues per device */
867                 return 0;
868 
869         dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args);
870         if (IS_ERR(dev))
871                 return PTR_ERR(dev);
872 
873         cgwb_bdi_register(bdi);
874         bdi->dev = dev;
875 
876         bdi_debug_register(bdi, dev_name(dev));
877         set_bit(WB_registered, &bdi->wb.state);
878 
879         spin_lock_bh(&bdi_lock);
880         list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
881         spin_unlock_bh(&bdi_lock);
882 
883         trace_writeback_bdi_register(bdi);
884         return 0;
885 }
886 EXPORT_SYMBOL(bdi_register_va);
887 
888 int bdi_register(struct backing_dev_info *bdi, const char *fmt, ...)
889 {
890         va_list args;
891         int ret;
892 
893         va_start(args, fmt);
894         ret = bdi_register_va(bdi, fmt, args);
895         va_end(args);
896         return ret;
897 }
898 EXPORT_SYMBOL(bdi_register);
899 
900 int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner)
901 {
902         int rc;
903 
904         rc = bdi_register(bdi, "%u:%u", MAJOR(owner->devt), MINOR(owner->devt));
905         if (rc)
906                 return rc;
907         /* Leaking owner reference... */
908         WARN_ON(bdi->owner);
909         bdi->owner = owner;
910         get_device(owner);
911         return 0;
912 }
913 EXPORT_SYMBOL(bdi_register_owner);
914 
915 /*
916  * Remove bdi from bdi_list, and ensure that it is no longer visible
917  */
918 static void bdi_remove_from_list(struct backing_dev_info *bdi)
919 {
920         spin_lock_bh(&bdi_lock);
921         list_del_rcu(&bdi->bdi_list);
922         spin_unlock_bh(&bdi_lock);
923 
924         synchronize_rcu_expedited();
925 }
926 
927 void bdi_unregister(struct backing_dev_info *bdi)
928 {
929         /* make sure nobody finds us on the bdi_list anymore */
930         bdi_remove_from_list(bdi);
931         wb_shutdown(&bdi->wb);
932         cgwb_bdi_unregister(bdi);
933 
934         if (bdi->dev) {
935                 bdi_debug_unregister(bdi);
936                 device_unregister(bdi->dev);
937                 bdi->dev = NULL;
938         }
939 
940         if (bdi->owner) {
941                 put_device(bdi->owner);
942                 bdi->owner = NULL;
943         }
944 }
945 
946 static void release_bdi(struct kref *ref)
947 {
948         struct backing_dev_info *bdi =
949                         container_of(ref, struct backing_dev_info, refcnt);
950 
951         if (test_bit(WB_registered, &bdi->wb.state))
952                 bdi_unregister(bdi);
953         WARN_ON_ONCE(bdi->dev);
954         wb_exit(&bdi->wb);
955         cgwb_bdi_exit(bdi);
956         kfree(bdi);
957 }
958 
959 void bdi_put(struct backing_dev_info *bdi)
960 {
961         kref_put(&bdi->refcnt, release_bdi);
962 }
963 EXPORT_SYMBOL(bdi_put);
964 
965 static wait_queue_head_t congestion_wqh[2] = {
966                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
967                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
968         };
969 static atomic_t nr_wb_congested[2];
970 
971 void clear_wb_congested(struct bdi_writeback_congested *congested, int sync)
972 {
973         wait_queue_head_t *wqh = &congestion_wqh[sync];
974         enum wb_congested_state bit;
975 
976         bit = sync ? WB_sync_congested : WB_async_congested;
977         if (test_and_clear_bit(bit, &congested->state))
978                 atomic_dec(&nr_wb_congested[sync]);
979         smp_mb__after_atomic();
980         if (waitqueue_active(wqh))
981                 wake_up(wqh);
982 }
983 EXPORT_SYMBOL(clear_wb_congested);
984 
985 void set_wb_congested(struct bdi_writeback_congested *congested, int sync)
986 {
987         enum wb_congested_state bit;
988 
989         bit = sync ? WB_sync_congested : WB_async_congested;
990         if (!test_and_set_bit(bit, &congested->state))
991                 atomic_inc(&nr_wb_congested[sync]);
992 }
993 EXPORT_SYMBOL(set_wb_congested);
994 
995 /**
996  * congestion_wait - wait for a backing_dev to become uncongested
997  * @sync: SYNC or ASYNC IO
998  * @timeout: timeout in jiffies
999  *
1000  * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
1001  * write congestion.  If no backing_devs are congested then just wait for the
1002  * next write to be completed.
1003  */
1004 long congestion_wait(int sync, long timeout)
1005 {
1006         long ret;
1007         unsigned long start = jiffies;
1008         DEFINE_WAIT(wait);
1009         wait_queue_head_t *wqh = &congestion_wqh[sync];
1010 
1011         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1012         ret = io_schedule_timeout(timeout);
1013         finish_wait(wqh, &wait);
1014 
1015         trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
1016                                         jiffies_to_usecs(jiffies - start));
1017 
1018         return ret;
1019 }
1020 EXPORT_SYMBOL(congestion_wait);
1021 
1022 /**
1023  * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a pgdat to complete writes
1024  * @sync: SYNC or ASYNC IO
1025  * @timeout: timeout in jiffies
1026  *
1027  * In the event of a congested backing_dev (any backing_dev) this waits
1028  * for up to @timeout jiffies for either a BDI to exit congestion of the
1029  * given @sync queue or a write to complete.
1030  *
1031  * The return value is 0 if the sleep is for the full timeout. Otherwise,
1032  * it is the number of jiffies that were still remaining when the function
1033  * returned. return_value == timeout implies the function did not sleep.
1034  */
1035 long wait_iff_congested(int sync, long timeout)
1036 {
1037         long ret;
1038         unsigned long start = jiffies;
1039         DEFINE_WAIT(wait);
1040         wait_queue_head_t *wqh = &congestion_wqh[sync];
1041 
1042         /*
1043          * If there is no congestion, yield if necessary instead
1044          * of sleeping on the congestion queue
1045          */
1046         if (atomic_read(&nr_wb_congested[sync]) == 0) {
1047                 cond_resched();
1048 
1049                 /* In case we scheduled, work out time remaining */
1050                 ret = timeout - (jiffies - start);
1051                 if (ret < 0)
1052                         ret = 0;
1053 
1054                 goto out;
1055         }
1056 
1057         /* Sleep until uncongested or a write happens */
1058         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1059         ret = io_schedule_timeout(timeout);
1060         finish_wait(wqh, &wait);
1061 
1062 out:
1063         trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
1064                                         jiffies_to_usecs(jiffies - start));
1065 
1066         return ret;
1067 }
1068 EXPORT_SYMBOL(wait_iff_congested);
1069 

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