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Linux/fs/fs-writeback.c

  1 /*
  2  * fs/fs-writeback.c
  3  *
  4  * Copyright (C) 2002, Linus Torvalds.
  5  *
  6  * Contains all the functions related to writing back and waiting
  7  * upon dirty inodes against superblocks, and writing back dirty
  8  * pages against inodes.  ie: data writeback.  Writeout of the
  9  * inode itself is not handled here.
 10  *
 11  * 10Apr2002    Andrew Morton
 12  *              Split out of fs/inode.c
 13  *              Additions for address_space-based writeback
 14  */
 15 
 16 #include <linux/kernel.h>
 17 #include <linux/export.h>
 18 #include <linux/spinlock.h>
 19 #include <linux/slab.h>
 20 #include <linux/sched.h>
 21 #include <linux/fs.h>
 22 #include <linux/mm.h>
 23 #include <linux/pagemap.h>
 24 #include <linux/kthread.h>
 25 #include <linux/writeback.h>
 26 #include <linux/blkdev.h>
 27 #include <linux/backing-dev.h>
 28 #include <linux/tracepoint.h>
 29 #include <linux/device.h>
 30 #include "internal.h"
 31 
 32 /*
 33  * 4MB minimal write chunk size
 34  */
 35 #define MIN_WRITEBACK_PAGES     (4096UL >> (PAGE_CACHE_SHIFT - 10))
 36 
 37 /*
 38  * Passed into wb_writeback(), essentially a subset of writeback_control
 39  */
 40 struct wb_writeback_work {
 41         long nr_pages;
 42         struct super_block *sb;
 43         unsigned long *older_than_this;
 44         enum writeback_sync_modes sync_mode;
 45         unsigned int tagged_writepages:1;
 46         unsigned int for_kupdate:1;
 47         unsigned int range_cyclic:1;
 48         unsigned int for_background:1;
 49         unsigned int for_sync:1;        /* sync(2) WB_SYNC_ALL writeback */
 50         enum wb_reason reason;          /* why was writeback initiated? */
 51 
 52         struct list_head list;          /* pending work list */
 53         struct completion *done;        /* set if the caller waits */
 54 };
 55 
 56 /**
 57  * writeback_in_progress - determine whether there is writeback in progress
 58  * @bdi: the device's backing_dev_info structure.
 59  *
 60  * Determine whether there is writeback waiting to be handled against a
 61  * backing device.
 62  */
 63 int writeback_in_progress(struct backing_dev_info *bdi)
 64 {
 65         return test_bit(BDI_writeback_running, &bdi->state);
 66 }
 67 EXPORT_SYMBOL(writeback_in_progress);
 68 
 69 static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
 70 {
 71         struct super_block *sb = inode->i_sb;
 72 
 73         if (sb_is_blkdev_sb(sb))
 74                 return inode->i_mapping->backing_dev_info;
 75 
 76         return sb->s_bdi;
 77 }
 78 
 79 static inline struct inode *wb_inode(struct list_head *head)
 80 {
 81         return list_entry(head, struct inode, i_wb_list);
 82 }
 83 
 84 /*
 85  * Include the creation of the trace points after defining the
 86  * wb_writeback_work structure and inline functions so that the definition
 87  * remains local to this file.
 88  */
 89 #define CREATE_TRACE_POINTS
 90 #include <trace/events/writeback.h>
 91 
 92 static void bdi_queue_work(struct backing_dev_info *bdi,
 93                            struct wb_writeback_work *work)
 94 {
 95         trace_writeback_queue(bdi, work);
 96 
 97         spin_lock_bh(&bdi->wb_lock);
 98         list_add_tail(&work->list, &bdi->work_list);
 99         spin_unlock_bh(&bdi->wb_lock);
100 
101         mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
102 }
103 
104 static void
105 __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
106                       bool range_cyclic, enum wb_reason reason)
107 {
108         struct wb_writeback_work *work;
109 
110         /*
111          * This is WB_SYNC_NONE writeback, so if allocation fails just
112          * wakeup the thread for old dirty data writeback
113          */
114         work = kzalloc(sizeof(*work), GFP_ATOMIC);
115         if (!work) {
116                 trace_writeback_nowork(bdi);
117                 mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
118                 return;
119         }
120 
121         work->sync_mode = WB_SYNC_NONE;
122         work->nr_pages  = nr_pages;
123         work->range_cyclic = range_cyclic;
124         work->reason    = reason;
125 
126         bdi_queue_work(bdi, work);
127 }
128 
129 /**
130  * bdi_start_writeback - start writeback
131  * @bdi: the backing device to write from
132  * @nr_pages: the number of pages to write
133  * @reason: reason why some writeback work was initiated
134  *
135  * Description:
136  *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
137  *   started when this function returns, we make no guarantees on
138  *   completion. Caller need not hold sb s_umount semaphore.
139  *
140  */
141 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
142                         enum wb_reason reason)
143 {
144         __bdi_start_writeback(bdi, nr_pages, true, reason);
145 }
146 
147 /**
148  * bdi_start_background_writeback - start background writeback
149  * @bdi: the backing device to write from
150  *
151  * Description:
152  *   This makes sure WB_SYNC_NONE background writeback happens. When
153  *   this function returns, it is only guaranteed that for given BDI
154  *   some IO is happening if we are over background dirty threshold.
155  *   Caller need not hold sb s_umount semaphore.
156  */
157 void bdi_start_background_writeback(struct backing_dev_info *bdi)
158 {
159         /*
160          * We just wake up the flusher thread. It will perform background
161          * writeback as soon as there is no other work to do.
162          */
163         trace_writeback_wake_background(bdi);
164         mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
165 }
166 
167 /*
168  * Remove the inode from the writeback list it is on.
169  */
170 void inode_wb_list_del(struct inode *inode)
171 {
172         struct backing_dev_info *bdi = inode_to_bdi(inode);
173 
174         spin_lock(&bdi->wb.list_lock);
175         list_del_init(&inode->i_wb_list);
176         spin_unlock(&bdi->wb.list_lock);
177 }
178 
179 /*
180  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
181  * furthest end of its superblock's dirty-inode list.
182  *
183  * Before stamping the inode's ->dirtied_when, we check to see whether it is
184  * already the most-recently-dirtied inode on the b_dirty list.  If that is
185  * the case then the inode must have been redirtied while it was being written
186  * out and we don't reset its dirtied_when.
187  */
188 static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
189 {
190         assert_spin_locked(&wb->list_lock);
191         if (!list_empty(&wb->b_dirty)) {
192                 struct inode *tail;
193 
194                 tail = wb_inode(wb->b_dirty.next);
195                 if (time_before(inode->dirtied_when, tail->dirtied_when))
196                         inode->dirtied_when = jiffies;
197         }
198         list_move(&inode->i_wb_list, &wb->b_dirty);
199 }
200 
201 /*
202  * requeue inode for re-scanning after bdi->b_io list is exhausted.
203  */
204 static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
205 {
206         assert_spin_locked(&wb->list_lock);
207         list_move(&inode->i_wb_list, &wb->b_more_io);
208 }
209 
210 static void inode_sync_complete(struct inode *inode)
211 {
212         inode->i_state &= ~I_SYNC;
213         /* If inode is clean an unused, put it into LRU now... */
214         inode_add_lru(inode);
215         /* Waiters must see I_SYNC cleared before being woken up */
216         smp_mb();
217         wake_up_bit(&inode->i_state, __I_SYNC);
218 }
219 
220 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
221 {
222         bool ret = time_after(inode->dirtied_when, t);
223 #ifndef CONFIG_64BIT
224         /*
225          * For inodes being constantly redirtied, dirtied_when can get stuck.
226          * It _appears_ to be in the future, but is actually in distant past.
227          * This test is necessary to prevent such wrapped-around relative times
228          * from permanently stopping the whole bdi writeback.
229          */
230         ret = ret && time_before_eq(inode->dirtied_when, jiffies);
231 #endif
232         return ret;
233 }
234 
235 /*
236  * Move expired (dirtied before work->older_than_this) dirty inodes from
237  * @delaying_queue to @dispatch_queue.
238  */
239 static int move_expired_inodes(struct list_head *delaying_queue,
240                                struct list_head *dispatch_queue,
241                                struct wb_writeback_work *work)
242 {
243         LIST_HEAD(tmp);
244         struct list_head *pos, *node;
245         struct super_block *sb = NULL;
246         struct inode *inode;
247         int do_sb_sort = 0;
248         int moved = 0;
249 
250         while (!list_empty(delaying_queue)) {
251                 inode = wb_inode(delaying_queue->prev);
252                 if (work->older_than_this &&
253                     inode_dirtied_after(inode, *work->older_than_this))
254                         break;
255                 list_move(&inode->i_wb_list, &tmp);
256                 moved++;
257                 if (sb_is_blkdev_sb(inode->i_sb))
258                         continue;
259                 if (sb && sb != inode->i_sb)
260                         do_sb_sort = 1;
261                 sb = inode->i_sb;
262         }
263 
264         /* just one sb in list, splice to dispatch_queue and we're done */
265         if (!do_sb_sort) {
266                 list_splice(&tmp, dispatch_queue);
267                 goto out;
268         }
269 
270         /* Move inodes from one superblock together */
271         while (!list_empty(&tmp)) {
272                 sb = wb_inode(tmp.prev)->i_sb;
273                 list_for_each_prev_safe(pos, node, &tmp) {
274                         inode = wb_inode(pos);
275                         if (inode->i_sb == sb)
276                                 list_move(&inode->i_wb_list, dispatch_queue);
277                 }
278         }
279 out:
280         return moved;
281 }
282 
283 /*
284  * Queue all expired dirty inodes for io, eldest first.
285  * Before
286  *         newly dirtied     b_dirty    b_io    b_more_io
287  *         =============>    gf         edc     BA
288  * After
289  *         newly dirtied     b_dirty    b_io    b_more_io
290  *         =============>    g          fBAedc
291  *                                           |
292  *                                           +--> dequeue for IO
293  */
294 static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
295 {
296         int moved;
297         assert_spin_locked(&wb->list_lock);
298         list_splice_init(&wb->b_more_io, &wb->b_io);
299         moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
300         trace_writeback_queue_io(wb, work, moved);
301 }
302 
303 static int write_inode(struct inode *inode, struct writeback_control *wbc)
304 {
305         int ret;
306 
307         if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
308                 trace_writeback_write_inode_start(inode, wbc);
309                 ret = inode->i_sb->s_op->write_inode(inode, wbc);
310                 trace_writeback_write_inode(inode, wbc);
311                 return ret;
312         }
313         return 0;
314 }
315 
316 /*
317  * Wait for writeback on an inode to complete. Called with i_lock held.
318  * Caller must make sure inode cannot go away when we drop i_lock.
319  */
320 static void __inode_wait_for_writeback(struct inode *inode)
321         __releases(inode->i_lock)
322         __acquires(inode->i_lock)
323 {
324         DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
325         wait_queue_head_t *wqh;
326 
327         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
328         while (inode->i_state & I_SYNC) {
329                 spin_unlock(&inode->i_lock);
330                 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
331                 spin_lock(&inode->i_lock);
332         }
333 }
334 
335 /*
336  * Wait for writeback on an inode to complete. Caller must have inode pinned.
337  */
338 void inode_wait_for_writeback(struct inode *inode)
339 {
340         spin_lock(&inode->i_lock);
341         __inode_wait_for_writeback(inode);
342         spin_unlock(&inode->i_lock);
343 }
344 
345 /*
346  * Sleep until I_SYNC is cleared. This function must be called with i_lock
347  * held and drops it. It is aimed for callers not holding any inode reference
348  * so once i_lock is dropped, inode can go away.
349  */
350 static void inode_sleep_on_writeback(struct inode *inode)
351         __releases(inode->i_lock)
352 {
353         DEFINE_WAIT(wait);
354         wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
355         int sleep;
356 
357         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
358         sleep = inode->i_state & I_SYNC;
359         spin_unlock(&inode->i_lock);
360         if (sleep)
361                 schedule();
362         finish_wait(wqh, &wait);
363 }
364 
365 /*
366  * Find proper writeback list for the inode depending on its current state and
367  * possibly also change of its state while we were doing writeback.  Here we
368  * handle things such as livelock prevention or fairness of writeback among
369  * inodes. This function can be called only by flusher thread - noone else
370  * processes all inodes in writeback lists and requeueing inodes behind flusher
371  * thread's back can have unexpected consequences.
372  */
373 static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
374                           struct writeback_control *wbc)
375 {
376         if (inode->i_state & I_FREEING)
377                 return;
378 
379         /*
380          * Sync livelock prevention. Each inode is tagged and synced in one
381          * shot. If still dirty, it will be redirty_tail()'ed below.  Update
382          * the dirty time to prevent enqueue and sync it again.
383          */
384         if ((inode->i_state & I_DIRTY) &&
385             (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
386                 inode->dirtied_when = jiffies;
387 
388         if (wbc->pages_skipped) {
389                 /*
390                  * writeback is not making progress due to locked
391                  * buffers. Skip this inode for now.
392                  */
393                 redirty_tail(inode, wb);
394                 return;
395         }
396 
397         if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
398                 /*
399                  * We didn't write back all the pages.  nfs_writepages()
400                  * sometimes bales out without doing anything.
401                  */
402                 if (wbc->nr_to_write <= 0) {
403                         /* Slice used up. Queue for next turn. */
404                         requeue_io(inode, wb);
405                 } else {
406                         /*
407                          * Writeback blocked by something other than
408                          * congestion. Delay the inode for some time to
409                          * avoid spinning on the CPU (100% iowait)
410                          * retrying writeback of the dirty page/inode
411                          * that cannot be performed immediately.
412                          */
413                         redirty_tail(inode, wb);
414                 }
415         } else if (inode->i_state & I_DIRTY) {
416                 /*
417                  * Filesystems can dirty the inode during writeback operations,
418                  * such as delayed allocation during submission or metadata
419                  * updates after data IO completion.
420                  */
421                 redirty_tail(inode, wb);
422         } else {
423                 /* The inode is clean. Remove from writeback lists. */
424                 list_del_init(&inode->i_wb_list);
425         }
426 }
427 
428 /*
429  * Write out an inode and its dirty pages. Do not update the writeback list
430  * linkage. That is left to the caller. The caller is also responsible for
431  * setting I_SYNC flag and calling inode_sync_complete() to clear it.
432  */
433 static int
434 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
435 {
436         struct address_space *mapping = inode->i_mapping;
437         long nr_to_write = wbc->nr_to_write;
438         unsigned dirty;
439         int ret;
440 
441         WARN_ON(!(inode->i_state & I_SYNC));
442 
443         trace_writeback_single_inode_start(inode, wbc, nr_to_write);
444 
445         ret = do_writepages(mapping, wbc);
446 
447         /*
448          * Make sure to wait on the data before writing out the metadata.
449          * This is important for filesystems that modify metadata on data
450          * I/O completion. We don't do it for sync(2) writeback because it has a
451          * separate, external IO completion path and ->sync_fs for guaranteeing
452          * inode metadata is written back correctly.
453          */
454         if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
455                 int err = filemap_fdatawait(mapping);
456                 if (ret == 0)
457                         ret = err;
458         }
459 
460         /*
461          * Some filesystems may redirty the inode during the writeback
462          * due to delalloc, clear dirty metadata flags right before
463          * write_inode()
464          */
465         spin_lock(&inode->i_lock);
466         /* Clear I_DIRTY_PAGES if we've written out all dirty pages */
467         if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
468                 inode->i_state &= ~I_DIRTY_PAGES;
469         dirty = inode->i_state & I_DIRTY;
470         inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
471         spin_unlock(&inode->i_lock);
472         /* Don't write the inode if only I_DIRTY_PAGES was set */
473         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
474                 int err = write_inode(inode, wbc);
475                 if (ret == 0)
476                         ret = err;
477         }
478         trace_writeback_single_inode(inode, wbc, nr_to_write);
479         return ret;
480 }
481 
482 /*
483  * Write out an inode's dirty pages. Either the caller has an active reference
484  * on the inode or the inode has I_WILL_FREE set.
485  *
486  * This function is designed to be called for writing back one inode which
487  * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
488  * and does more profound writeback list handling in writeback_sb_inodes().
489  */
490 static int
491 writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
492                        struct writeback_control *wbc)
493 {
494         int ret = 0;
495 
496         spin_lock(&inode->i_lock);
497         if (!atomic_read(&inode->i_count))
498                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
499         else
500                 WARN_ON(inode->i_state & I_WILL_FREE);
501 
502         if (inode->i_state & I_SYNC) {
503                 if (wbc->sync_mode != WB_SYNC_ALL)
504                         goto out;
505                 /*
506                  * It's a data-integrity sync. We must wait. Since callers hold
507                  * inode reference or inode has I_WILL_FREE set, it cannot go
508                  * away under us.
509                  */
510                 __inode_wait_for_writeback(inode);
511         }
512         WARN_ON(inode->i_state & I_SYNC);
513         /*
514          * Skip inode if it is clean and we have no outstanding writeback in
515          * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
516          * function since flusher thread may be doing for example sync in
517          * parallel and if we move the inode, it could get skipped. So here we
518          * make sure inode is on some writeback list and leave it there unless
519          * we have completely cleaned the inode.
520          */
521         if (!(inode->i_state & I_DIRTY) &&
522             (wbc->sync_mode != WB_SYNC_ALL ||
523              !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
524                 goto out;
525         inode->i_state |= I_SYNC;
526         spin_unlock(&inode->i_lock);
527 
528         ret = __writeback_single_inode(inode, wbc);
529 
530         spin_lock(&wb->list_lock);
531         spin_lock(&inode->i_lock);
532         /*
533          * If inode is clean, remove it from writeback lists. Otherwise don't
534          * touch it. See comment above for explanation.
535          */
536         if (!(inode->i_state & I_DIRTY))
537                 list_del_init(&inode->i_wb_list);
538         spin_unlock(&wb->list_lock);
539         inode_sync_complete(inode);
540 out:
541         spin_unlock(&inode->i_lock);
542         return ret;
543 }
544 
545 static long writeback_chunk_size(struct backing_dev_info *bdi,
546                                  struct wb_writeback_work *work)
547 {
548         long pages;
549 
550         /*
551          * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
552          * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
553          * here avoids calling into writeback_inodes_wb() more than once.
554          *
555          * The intended call sequence for WB_SYNC_ALL writeback is:
556          *
557          *      wb_writeback()
558          *          writeback_sb_inodes()       <== called only once
559          *              write_cache_pages()     <== called once for each inode
560          *                   (quickly) tag currently dirty pages
561          *                   (maybe slowly) sync all tagged pages
562          */
563         if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
564                 pages = LONG_MAX;
565         else {
566                 pages = min(bdi->avg_write_bandwidth / 2,
567                             global_dirty_limit / DIRTY_SCOPE);
568                 pages = min(pages, work->nr_pages);
569                 pages = round_down(pages + MIN_WRITEBACK_PAGES,
570                                    MIN_WRITEBACK_PAGES);
571         }
572 
573         return pages;
574 }
575 
576 /*
577  * Write a portion of b_io inodes which belong to @sb.
578  *
579  * Return the number of pages and/or inodes written.
580  */
581 static long writeback_sb_inodes(struct super_block *sb,
582                                 struct bdi_writeback *wb,
583                                 struct wb_writeback_work *work)
584 {
585         struct writeback_control wbc = {
586                 .sync_mode              = work->sync_mode,
587                 .tagged_writepages      = work->tagged_writepages,
588                 .for_kupdate            = work->for_kupdate,
589                 .for_background         = work->for_background,
590                 .for_sync               = work->for_sync,
591                 .range_cyclic           = work->range_cyclic,
592                 .range_start            = 0,
593                 .range_end              = LLONG_MAX,
594         };
595         unsigned long start_time = jiffies;
596         long write_chunk;
597         long wrote = 0;  /* count both pages and inodes */
598 
599         while (!list_empty(&wb->b_io)) {
600                 struct inode *inode = wb_inode(wb->b_io.prev);
601 
602                 if (inode->i_sb != sb) {
603                         if (work->sb) {
604                                 /*
605                                  * We only want to write back data for this
606                                  * superblock, move all inodes not belonging
607                                  * to it back onto the dirty list.
608                                  */
609                                 redirty_tail(inode, wb);
610                                 continue;
611                         }
612 
613                         /*
614                          * The inode belongs to a different superblock.
615                          * Bounce back to the caller to unpin this and
616                          * pin the next superblock.
617                          */
618                         break;
619                 }
620 
621                 /*
622                  * Don't bother with new inodes or inodes being freed, first
623                  * kind does not need periodic writeout yet, and for the latter
624                  * kind writeout is handled by the freer.
625                  */
626                 spin_lock(&inode->i_lock);
627                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
628                         spin_unlock(&inode->i_lock);
629                         redirty_tail(inode, wb);
630                         continue;
631                 }
632                 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
633                         /*
634                          * If this inode is locked for writeback and we are not
635                          * doing writeback-for-data-integrity, move it to
636                          * b_more_io so that writeback can proceed with the
637                          * other inodes on s_io.
638                          *
639                          * We'll have another go at writing back this inode
640                          * when we completed a full scan of b_io.
641                          */
642                         spin_unlock(&inode->i_lock);
643                         requeue_io(inode, wb);
644                         trace_writeback_sb_inodes_requeue(inode);
645                         continue;
646                 }
647                 spin_unlock(&wb->list_lock);
648 
649                 /*
650                  * We already requeued the inode if it had I_SYNC set and we
651                  * are doing WB_SYNC_NONE writeback. So this catches only the
652                  * WB_SYNC_ALL case.
653                  */
654                 if (inode->i_state & I_SYNC) {
655                         /* Wait for I_SYNC. This function drops i_lock... */
656                         inode_sleep_on_writeback(inode);
657                         /* Inode may be gone, start again */
658                         spin_lock(&wb->list_lock);
659                         continue;
660                 }
661                 inode->i_state |= I_SYNC;
662                 spin_unlock(&inode->i_lock);
663 
664                 write_chunk = writeback_chunk_size(wb->bdi, work);
665                 wbc.nr_to_write = write_chunk;
666                 wbc.pages_skipped = 0;
667 
668                 /*
669                  * We use I_SYNC to pin the inode in memory. While it is set
670                  * evict_inode() will wait so the inode cannot be freed.
671                  */
672                 __writeback_single_inode(inode, &wbc);
673 
674                 work->nr_pages -= write_chunk - wbc.nr_to_write;
675                 wrote += write_chunk - wbc.nr_to_write;
676                 spin_lock(&wb->list_lock);
677                 spin_lock(&inode->i_lock);
678                 if (!(inode->i_state & I_DIRTY))
679                         wrote++;
680                 requeue_inode(inode, wb, &wbc);
681                 inode_sync_complete(inode);
682                 spin_unlock(&inode->i_lock);
683                 cond_resched_lock(&wb->list_lock);
684                 /*
685                  * bail out to wb_writeback() often enough to check
686                  * background threshold and other termination conditions.
687                  */
688                 if (wrote) {
689                         if (time_is_before_jiffies(start_time + HZ / 10UL))
690                                 break;
691                         if (work->nr_pages <= 0)
692                                 break;
693                 }
694         }
695         return wrote;
696 }
697 
698 static long __writeback_inodes_wb(struct bdi_writeback *wb,
699                                   struct wb_writeback_work *work)
700 {
701         unsigned long start_time = jiffies;
702         long wrote = 0;
703 
704         while (!list_empty(&wb->b_io)) {
705                 struct inode *inode = wb_inode(wb->b_io.prev);
706                 struct super_block *sb = inode->i_sb;
707 
708                 if (!grab_super_passive(sb)) {
709                         /*
710                          * grab_super_passive() may fail consistently due to
711                          * s_umount being grabbed by someone else. Don't use
712                          * requeue_io() to avoid busy retrying the inode/sb.
713                          */
714                         redirty_tail(inode, wb);
715                         continue;
716                 }
717                 wrote += writeback_sb_inodes(sb, wb, work);
718                 drop_super(sb);
719 
720                 /* refer to the same tests at the end of writeback_sb_inodes */
721                 if (wrote) {
722                         if (time_is_before_jiffies(start_time + HZ / 10UL))
723                                 break;
724                         if (work->nr_pages <= 0)
725                                 break;
726                 }
727         }
728         /* Leave any unwritten inodes on b_io */
729         return wrote;
730 }
731 
732 static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
733                                 enum wb_reason reason)
734 {
735         struct wb_writeback_work work = {
736                 .nr_pages       = nr_pages,
737                 .sync_mode      = WB_SYNC_NONE,
738                 .range_cyclic   = 1,
739                 .reason         = reason,
740         };
741 
742         spin_lock(&wb->list_lock);
743         if (list_empty(&wb->b_io))
744                 queue_io(wb, &work);
745         __writeback_inodes_wb(wb, &work);
746         spin_unlock(&wb->list_lock);
747 
748         return nr_pages - work.nr_pages;
749 }
750 
751 static bool over_bground_thresh(struct backing_dev_info *bdi)
752 {
753         unsigned long background_thresh, dirty_thresh;
754 
755         global_dirty_limits(&background_thresh, &dirty_thresh);
756 
757         if (global_page_state(NR_FILE_DIRTY) +
758             global_page_state(NR_UNSTABLE_NFS) > background_thresh)
759                 return true;
760 
761         if (bdi_stat(bdi, BDI_RECLAIMABLE) >
762                                 bdi_dirty_limit(bdi, background_thresh))
763                 return true;
764 
765         return false;
766 }
767 
768 /*
769  * Called under wb->list_lock. If there are multiple wb per bdi,
770  * only the flusher working on the first wb should do it.
771  */
772 static void wb_update_bandwidth(struct bdi_writeback *wb,
773                                 unsigned long start_time)
774 {
775         __bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
776 }
777 
778 /*
779  * Explicit flushing or periodic writeback of "old" data.
780  *
781  * Define "old": the first time one of an inode's pages is dirtied, we mark the
782  * dirtying-time in the inode's address_space.  So this periodic writeback code
783  * just walks the superblock inode list, writing back any inodes which are
784  * older than a specific point in time.
785  *
786  * Try to run once per dirty_writeback_interval.  But if a writeback event
787  * takes longer than a dirty_writeback_interval interval, then leave a
788  * one-second gap.
789  *
790  * older_than_this takes precedence over nr_to_write.  So we'll only write back
791  * all dirty pages if they are all attached to "old" mappings.
792  */
793 static long wb_writeback(struct bdi_writeback *wb,
794                          struct wb_writeback_work *work)
795 {
796         unsigned long wb_start = jiffies;
797         long nr_pages = work->nr_pages;
798         unsigned long oldest_jif;
799         struct inode *inode;
800         long progress;
801 
802         oldest_jif = jiffies;
803         work->older_than_this = &oldest_jif;
804 
805         spin_lock(&wb->list_lock);
806         for (;;) {
807                 /*
808                  * Stop writeback when nr_pages has been consumed
809                  */
810                 if (work->nr_pages <= 0)
811                         break;
812 
813                 /*
814                  * Background writeout and kupdate-style writeback may
815                  * run forever. Stop them if there is other work to do
816                  * so that e.g. sync can proceed. They'll be restarted
817                  * after the other works are all done.
818                  */
819                 if ((work->for_background || work->for_kupdate) &&
820                     !list_empty(&wb->bdi->work_list))
821                         break;
822 
823                 /*
824                  * For background writeout, stop when we are below the
825                  * background dirty threshold
826                  */
827                 if (work->for_background && !over_bground_thresh(wb->bdi))
828                         break;
829 
830                 /*
831                  * Kupdate and background works are special and we want to
832                  * include all inodes that need writing. Livelock avoidance is
833                  * handled by these works yielding to any other work so we are
834                  * safe.
835                  */
836                 if (work->for_kupdate) {
837                         oldest_jif = jiffies -
838                                 msecs_to_jiffies(dirty_expire_interval * 10);
839                 } else if (work->for_background)
840                         oldest_jif = jiffies;
841 
842                 trace_writeback_start(wb->bdi, work);
843                 if (list_empty(&wb->b_io))
844                         queue_io(wb, work);
845                 if (work->sb)
846                         progress = writeback_sb_inodes(work->sb, wb, work);
847                 else
848                         progress = __writeback_inodes_wb(wb, work);
849                 trace_writeback_written(wb->bdi, work);
850 
851                 wb_update_bandwidth(wb, wb_start);
852 
853                 /*
854                  * Did we write something? Try for more
855                  *
856                  * Dirty inodes are moved to b_io for writeback in batches.
857                  * The completion of the current batch does not necessarily
858                  * mean the overall work is done. So we keep looping as long
859                  * as made some progress on cleaning pages or inodes.
860                  */
861                 if (progress)
862                         continue;
863                 /*
864                  * No more inodes for IO, bail
865                  */
866                 if (list_empty(&wb->b_more_io))
867                         break;
868                 /*
869                  * Nothing written. Wait for some inode to
870                  * become available for writeback. Otherwise
871                  * we'll just busyloop.
872                  */
873                 if (!list_empty(&wb->b_more_io))  {
874                         trace_writeback_wait(wb->bdi, work);
875                         inode = wb_inode(wb->b_more_io.prev);
876                         spin_lock(&inode->i_lock);
877                         spin_unlock(&wb->list_lock);
878                         /* This function drops i_lock... */
879                         inode_sleep_on_writeback(inode);
880                         spin_lock(&wb->list_lock);
881                 }
882         }
883         spin_unlock(&wb->list_lock);
884 
885         return nr_pages - work->nr_pages;
886 }
887 
888 /*
889  * Return the next wb_writeback_work struct that hasn't been processed yet.
890  */
891 static struct wb_writeback_work *
892 get_next_work_item(struct backing_dev_info *bdi)
893 {
894         struct wb_writeback_work *work = NULL;
895 
896         spin_lock_bh(&bdi->wb_lock);
897         if (!list_empty(&bdi->work_list)) {
898                 work = list_entry(bdi->work_list.next,
899                                   struct wb_writeback_work, list);
900                 list_del_init(&work->list);
901         }
902         spin_unlock_bh(&bdi->wb_lock);
903         return work;
904 }
905 
906 /*
907  * Add in the number of potentially dirty inodes, because each inode
908  * write can dirty pagecache in the underlying blockdev.
909  */
910 static unsigned long get_nr_dirty_pages(void)
911 {
912         return global_page_state(NR_FILE_DIRTY) +
913                 global_page_state(NR_UNSTABLE_NFS) +
914                 get_nr_dirty_inodes();
915 }
916 
917 static long wb_check_background_flush(struct bdi_writeback *wb)
918 {
919         if (over_bground_thresh(wb->bdi)) {
920 
921                 struct wb_writeback_work work = {
922                         .nr_pages       = LONG_MAX,
923                         .sync_mode      = WB_SYNC_NONE,
924                         .for_background = 1,
925                         .range_cyclic   = 1,
926                         .reason         = WB_REASON_BACKGROUND,
927                 };
928 
929                 return wb_writeback(wb, &work);
930         }
931 
932         return 0;
933 }
934 
935 static long wb_check_old_data_flush(struct bdi_writeback *wb)
936 {
937         unsigned long expired;
938         long nr_pages;
939 
940         /*
941          * When set to zero, disable periodic writeback
942          */
943         if (!dirty_writeback_interval)
944                 return 0;
945 
946         expired = wb->last_old_flush +
947                         msecs_to_jiffies(dirty_writeback_interval * 10);
948         if (time_before(jiffies, expired))
949                 return 0;
950 
951         wb->last_old_flush = jiffies;
952         nr_pages = get_nr_dirty_pages();
953 
954         if (nr_pages) {
955                 struct wb_writeback_work work = {
956                         .nr_pages       = nr_pages,
957                         .sync_mode      = WB_SYNC_NONE,
958                         .for_kupdate    = 1,
959                         .range_cyclic   = 1,
960                         .reason         = WB_REASON_PERIODIC,
961                 };
962 
963                 return wb_writeback(wb, &work);
964         }
965 
966         return 0;
967 }
968 
969 /*
970  * Retrieve work items and do the writeback they describe
971  */
972 static long wb_do_writeback(struct bdi_writeback *wb)
973 {
974         struct backing_dev_info *bdi = wb->bdi;
975         struct wb_writeback_work *work;
976         long wrote = 0;
977 
978         set_bit(BDI_writeback_running, &wb->bdi->state);
979         while ((work = get_next_work_item(bdi)) != NULL) {
980 
981                 trace_writeback_exec(bdi, work);
982 
983                 wrote += wb_writeback(wb, work);
984 
985                 /*
986                  * Notify the caller of completion if this is a synchronous
987                  * work item, otherwise just free it.
988                  */
989                 if (work->done)
990                         complete(work->done);
991                 else
992                         kfree(work);
993         }
994 
995         /*
996          * Check for periodic writeback, kupdated() style
997          */
998         wrote += wb_check_old_data_flush(wb);
999         wrote += wb_check_background_flush(wb);
1000         clear_bit(BDI_writeback_running, &wb->bdi->state);
1001 
1002         return wrote;
1003 }
1004 
1005 /*
1006  * Handle writeback of dirty data for the device backed by this bdi. Also
1007  * reschedules periodically and does kupdated style flushing.
1008  */
1009 void bdi_writeback_workfn(struct work_struct *work)
1010 {
1011         struct bdi_writeback *wb = container_of(to_delayed_work(work),
1012                                                 struct bdi_writeback, dwork);
1013         struct backing_dev_info *bdi = wb->bdi;
1014         long pages_written;
1015 
1016         set_worker_desc("flush-%s", dev_name(bdi->dev));
1017         current->flags |= PF_SWAPWRITE;
1018 
1019         if (likely(!current_is_workqueue_rescuer() ||
1020                    list_empty(&bdi->bdi_list))) {
1021                 /*
1022                  * The normal path.  Keep writing back @bdi until its
1023                  * work_list is empty.  Note that this path is also taken
1024                  * if @bdi is shutting down even when we're running off the
1025                  * rescuer as work_list needs to be drained.
1026                  */
1027                 do {
1028                         pages_written = wb_do_writeback(wb);
1029                         trace_writeback_pages_written(pages_written);
1030                 } while (!list_empty(&bdi->work_list));
1031         } else {
1032                 /*
1033                  * bdi_wq can't get enough workers and we're running off
1034                  * the emergency worker.  Don't hog it.  Hopefully, 1024 is
1035                  * enough for efficient IO.
1036                  */
1037                 pages_written = writeback_inodes_wb(&bdi->wb, 1024,
1038                                                     WB_REASON_FORKER_THREAD);
1039                 trace_writeback_pages_written(pages_written);
1040         }
1041 
1042         if (!list_empty(&bdi->work_list) ||
1043             (wb_has_dirty_io(wb) && dirty_writeback_interval))
1044                 queue_delayed_work(bdi_wq, &wb->dwork,
1045                         msecs_to_jiffies(dirty_writeback_interval * 10));
1046 
1047         current->flags &= ~PF_SWAPWRITE;
1048 }
1049 
1050 /*
1051  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
1052  * the whole world.
1053  */
1054 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
1055 {
1056         struct backing_dev_info *bdi;
1057 
1058         if (!nr_pages)
1059                 nr_pages = get_nr_dirty_pages();
1060 
1061         rcu_read_lock();
1062         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
1063                 if (!bdi_has_dirty_io(bdi))
1064                         continue;
1065                 __bdi_start_writeback(bdi, nr_pages, false, reason);
1066         }
1067         rcu_read_unlock();
1068 }
1069 
1070 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
1071 {
1072         if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
1073                 struct dentry *dentry;
1074                 const char *name = "?";
1075 
1076                 dentry = d_find_alias(inode);
1077                 if (dentry) {
1078                         spin_lock(&dentry->d_lock);
1079                         name = (const char *) dentry->d_name.name;
1080                 }
1081                 printk(KERN_DEBUG
1082                        "%s(%d): dirtied inode %lu (%s) on %s\n",
1083                        current->comm, task_pid_nr(current), inode->i_ino,
1084                        name, inode->i_sb->s_id);
1085                 if (dentry) {
1086                         spin_unlock(&dentry->d_lock);
1087                         dput(dentry);
1088                 }
1089         }
1090 }
1091 
1092 /**
1093  *      __mark_inode_dirty -    internal function
1094  *      @inode: inode to mark
1095  *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
1096  *      Mark an inode as dirty. Callers should use mark_inode_dirty or
1097  *      mark_inode_dirty_sync.
1098  *
1099  * Put the inode on the super block's dirty list.
1100  *
1101  * CAREFUL! We mark it dirty unconditionally, but move it onto the
1102  * dirty list only if it is hashed or if it refers to a blockdev.
1103  * If it was not hashed, it will never be added to the dirty list
1104  * even if it is later hashed, as it will have been marked dirty already.
1105  *
1106  * In short, make sure you hash any inodes _before_ you start marking
1107  * them dirty.
1108  *
1109  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1110  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
1111  * the kernel-internal blockdev inode represents the dirtying time of the
1112  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
1113  * page->mapping->host, so the page-dirtying time is recorded in the internal
1114  * blockdev inode.
1115  */
1116 void __mark_inode_dirty(struct inode *inode, int flags)
1117 {
1118         struct super_block *sb = inode->i_sb;
1119         struct backing_dev_info *bdi = NULL;
1120 
1121         /*
1122          * Don't do this for I_DIRTY_PAGES - that doesn't actually
1123          * dirty the inode itself
1124          */
1125         if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1126                 trace_writeback_dirty_inode_start(inode, flags);
1127 
1128                 if (sb->s_op->dirty_inode)
1129                         sb->s_op->dirty_inode(inode, flags);
1130 
1131                 trace_writeback_dirty_inode(inode, flags);
1132         }
1133 
1134         /*
1135          * make sure that changes are seen by all cpus before we test i_state
1136          * -- mikulas
1137          */
1138         smp_mb();
1139 
1140         /* avoid the locking if we can */
1141         if ((inode->i_state & flags) == flags)
1142                 return;
1143 
1144         if (unlikely(block_dump))
1145                 block_dump___mark_inode_dirty(inode);
1146 
1147         spin_lock(&inode->i_lock);
1148         if ((inode->i_state & flags) != flags) {
1149                 const int was_dirty = inode->i_state & I_DIRTY;
1150 
1151                 inode->i_state |= flags;
1152 
1153                 /*
1154                  * If the inode is being synced, just update its dirty state.
1155                  * The unlocker will place the inode on the appropriate
1156                  * superblock list, based upon its state.
1157                  */
1158                 if (inode->i_state & I_SYNC)
1159                         goto out_unlock_inode;
1160 
1161                 /*
1162                  * Only add valid (hashed) inodes to the superblock's
1163                  * dirty list.  Add blockdev inodes as well.
1164                  */
1165                 if (!S_ISBLK(inode->i_mode)) {
1166                         if (inode_unhashed(inode))
1167                                 goto out_unlock_inode;
1168                 }
1169                 if (inode->i_state & I_FREEING)
1170                         goto out_unlock_inode;
1171 
1172                 /*
1173                  * If the inode was already on b_dirty/b_io/b_more_io, don't
1174                  * reposition it (that would break b_dirty time-ordering).
1175                  */
1176                 if (!was_dirty) {
1177                         bool wakeup_bdi = false;
1178                         bdi = inode_to_bdi(inode);
1179 
1180                         spin_unlock(&inode->i_lock);
1181                         spin_lock(&bdi->wb.list_lock);
1182                         if (bdi_cap_writeback_dirty(bdi)) {
1183                                 WARN(!test_bit(BDI_registered, &bdi->state),
1184                                      "bdi-%s not registered\n", bdi->name);
1185 
1186                                 /*
1187                                  * If this is the first dirty inode for this
1188                                  * bdi, we have to wake-up the corresponding
1189                                  * bdi thread to make sure background
1190                                  * write-back happens later.
1191                                  */
1192                                 if (!wb_has_dirty_io(&bdi->wb))
1193                                         wakeup_bdi = true;
1194                         }
1195 
1196                         inode->dirtied_when = jiffies;
1197                         list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1198                         spin_unlock(&bdi->wb.list_lock);
1199 
1200                         if (wakeup_bdi)
1201                                 bdi_wakeup_thread_delayed(bdi);
1202                         return;
1203                 }
1204         }
1205 out_unlock_inode:
1206         spin_unlock(&inode->i_lock);
1207 
1208 }
1209 EXPORT_SYMBOL(__mark_inode_dirty);
1210 
1211 static void wait_sb_inodes(struct super_block *sb)
1212 {
1213         struct inode *inode, *old_inode = NULL;
1214 
1215         /*
1216          * We need to be protected against the filesystem going from
1217          * r/o to r/w or vice versa.
1218          */
1219         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1220 
1221         spin_lock(&inode_sb_list_lock);
1222 
1223         /*
1224          * Data integrity sync. Must wait for all pages under writeback,
1225          * because there may have been pages dirtied before our sync
1226          * call, but which had writeout started before we write it out.
1227          * In which case, the inode may not be on the dirty list, but
1228          * we still have to wait for that writeout.
1229          */
1230         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1231                 struct address_space *mapping = inode->i_mapping;
1232 
1233                 spin_lock(&inode->i_lock);
1234                 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
1235                     (mapping->nrpages == 0)) {
1236                         spin_unlock(&inode->i_lock);
1237                         continue;
1238                 }
1239                 __iget(inode);
1240                 spin_unlock(&inode->i_lock);
1241                 spin_unlock(&inode_sb_list_lock);
1242 
1243                 /*
1244                  * We hold a reference to 'inode' so it couldn't have been
1245                  * removed from s_inodes list while we dropped the
1246                  * inode_sb_list_lock.  We cannot iput the inode now as we can
1247                  * be holding the last reference and we cannot iput it under
1248                  * inode_sb_list_lock. So we keep the reference and iput it
1249                  * later.
1250                  */
1251                 iput(old_inode);
1252                 old_inode = inode;
1253 
1254                 filemap_fdatawait(mapping);
1255 
1256                 cond_resched();
1257 
1258                 spin_lock(&inode_sb_list_lock);
1259         }
1260         spin_unlock(&inode_sb_list_lock);
1261         iput(old_inode);
1262 }
1263 
1264 /**
1265  * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
1266  * @sb: the superblock
1267  * @nr: the number of pages to write
1268  * @reason: reason why some writeback work initiated
1269  *
1270  * Start writeback on some inodes on this super_block. No guarantees are made
1271  * on how many (if any) will be written, and this function does not wait
1272  * for IO completion of submitted IO.
1273  */
1274 void writeback_inodes_sb_nr(struct super_block *sb,
1275                             unsigned long nr,
1276                             enum wb_reason reason)
1277 {
1278         DECLARE_COMPLETION_ONSTACK(done);
1279         struct wb_writeback_work work = {
1280                 .sb                     = sb,
1281                 .sync_mode              = WB_SYNC_NONE,
1282                 .tagged_writepages      = 1,
1283                 .done                   = &done,
1284                 .nr_pages               = nr,
1285                 .reason                 = reason,
1286         };
1287 
1288         if (sb->s_bdi == &noop_backing_dev_info)
1289                 return;
1290         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1291         bdi_queue_work(sb->s_bdi, &work);
1292         wait_for_completion(&done);
1293 }
1294 EXPORT_SYMBOL(writeback_inodes_sb_nr);
1295 
1296 /**
1297  * writeback_inodes_sb  -       writeback dirty inodes from given super_block
1298  * @sb: the superblock
1299  * @reason: reason why some writeback work was initiated
1300  *
1301  * Start writeback on some inodes on this super_block. No guarantees are made
1302  * on how many (if any) will be written, and this function does not wait
1303  * for IO completion of submitted IO.
1304  */
1305 void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1306 {
1307         return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1308 }
1309 EXPORT_SYMBOL(writeback_inodes_sb);
1310 
1311 /**
1312  * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
1313  * @sb: the superblock
1314  * @nr: the number of pages to write
1315  * @reason: the reason of writeback
1316  *
1317  * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
1318  * Returns 1 if writeback was started, 0 if not.
1319  */
1320 int try_to_writeback_inodes_sb_nr(struct super_block *sb,
1321                                   unsigned long nr,
1322                                   enum wb_reason reason)
1323 {
1324         if (writeback_in_progress(sb->s_bdi))
1325                 return 1;
1326 
1327         if (!down_read_trylock(&sb->s_umount))
1328                 return 0;
1329 
1330         writeback_inodes_sb_nr(sb, nr, reason);
1331         up_read(&sb->s_umount);
1332         return 1;
1333 }
1334 EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);
1335 
1336 /**
1337  * try_to_writeback_inodes_sb - try to start writeback if none underway
1338  * @sb: the superblock
1339  * @reason: reason why some writeback work was initiated
1340  *
1341  * Implement by try_to_writeback_inodes_sb_nr()
1342  * Returns 1 if writeback was started, 0 if not.
1343  */
1344 int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
1345 {
1346         return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
1347 }
1348 EXPORT_SYMBOL(try_to_writeback_inodes_sb);
1349 
1350 /**
1351  * sync_inodes_sb       -       sync sb inode pages
1352  * @sb: the superblock
1353  *
1354  * This function writes and waits on any dirty inode belonging to this
1355  * super_block.
1356  */
1357 void sync_inodes_sb(struct super_block *sb)
1358 {
1359         DECLARE_COMPLETION_ONSTACK(done);
1360         struct wb_writeback_work work = {
1361                 .sb             = sb,
1362                 .sync_mode      = WB_SYNC_ALL,
1363                 .nr_pages       = LONG_MAX,
1364                 .range_cyclic   = 0,
1365                 .done           = &done,
1366                 .reason         = WB_REASON_SYNC,
1367                 .for_sync       = 1,
1368         };
1369 
1370         /* Nothing to do? */
1371         if (sb->s_bdi == &noop_backing_dev_info)
1372                 return;
1373         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1374 
1375         bdi_queue_work(sb->s_bdi, &work);
1376         wait_for_completion(&done);
1377 
1378         wait_sb_inodes(sb);
1379 }
1380 EXPORT_SYMBOL(sync_inodes_sb);
1381 
1382 /**
1383  * write_inode_now      -       write an inode to disk
1384  * @inode: inode to write to disk
1385  * @sync: whether the write should be synchronous or not
1386  *
1387  * This function commits an inode to disk immediately if it is dirty. This is
1388  * primarily needed by knfsd.
1389  *
1390  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1391  */
1392 int write_inode_now(struct inode *inode, int sync)
1393 {
1394         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
1395         struct writeback_control wbc = {
1396                 .nr_to_write = LONG_MAX,
1397                 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1398                 .range_start = 0,
1399                 .range_end = LLONG_MAX,
1400         };
1401 
1402         if (!mapping_cap_writeback_dirty(inode->i_mapping))
1403                 wbc.nr_to_write = 0;
1404 
1405         might_sleep();
1406         return writeback_single_inode(inode, wb, &wbc);
1407 }
1408 EXPORT_SYMBOL(write_inode_now);
1409 
1410 /**
1411  * sync_inode - write an inode and its pages to disk.
1412  * @inode: the inode to sync
1413  * @wbc: controls the writeback mode
1414  *
1415  * sync_inode() will write an inode and its pages to disk.  It will also
1416  * correctly update the inode on its superblock's dirty inode lists and will
1417  * update inode->i_state.
1418  *
1419  * The caller must have a ref on the inode.
1420  */
1421 int sync_inode(struct inode *inode, struct writeback_control *wbc)
1422 {
1423         return writeback_single_inode(inode, &inode_to_bdi(inode)->wb, wbc);
1424 }
1425 EXPORT_SYMBOL(sync_inode);
1426 
1427 /**
1428  * sync_inode_metadata - write an inode to disk
1429  * @inode: the inode to sync
1430  * @wait: wait for I/O to complete.
1431  *
1432  * Write an inode to disk and adjust its dirty state after completion.
1433  *
1434  * Note: only writes the actual inode, no associated data or other metadata.
1435  */
1436 int sync_inode_metadata(struct inode *inode, int wait)
1437 {
1438         struct writeback_control wbc = {
1439                 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1440                 .nr_to_write = 0, /* metadata-only */
1441         };
1442 
1443         return sync_inode(inode, &wbc);
1444 }
1445 EXPORT_SYMBOL(sync_inode_metadata);
1446 

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