x86: Make Dell Latitude E6420 use reboot=pci
[linux-2.6.git] / 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/module.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/kthread.h>
24 #include <linux/freezer.h>
25 #include <linux/writeback.h>
26 #include <linux/blkdev.h>
27 #include <linux/backing-dev.h>
28 #include <linux/buffer_head.h>
29 #include <linux/tracepoint.h>
30 #include "internal.h"
31
32 /*
33  * Passed into wb_writeback(), essentially a subset of writeback_control
34  */
35 struct wb_writeback_work {
36         long nr_pages;
37         struct super_block *sb;
38         enum writeback_sync_modes sync_mode;
39         unsigned int for_kupdate:1;
40         unsigned int range_cyclic:1;
41         unsigned int for_background:1;
42
43         struct list_head list;          /* pending work list */
44         struct completion *done;        /* set if the caller waits */
45 };
46
47 /*
48  * Include the creation of the trace points after defining the
49  * wb_writeback_work structure so that the definition remains local to this
50  * file.
51  */
52 #define CREATE_TRACE_POINTS
53 #include <trace/events/writeback.h>
54
55 /*
56  * We don't actually have pdflush, but this one is exported though /proc...
57  */
58 int nr_pdflush_threads;
59
60 /**
61  * writeback_in_progress - determine whether there is writeback in progress
62  * @bdi: the device's backing_dev_info structure.
63  *
64  * Determine whether there is writeback waiting to be handled against a
65  * backing device.
66  */
67 int writeback_in_progress(struct backing_dev_info *bdi)
68 {
69         return test_bit(BDI_writeback_running, &bdi->state);
70 }
71
72 static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
73 {
74         struct super_block *sb = inode->i_sb;
75
76         if (strcmp(sb->s_type->name, "bdev") == 0)
77                 return inode->i_mapping->backing_dev_info;
78
79         return sb->s_bdi;
80 }
81
82 static inline struct inode *wb_inode(struct list_head *head)
83 {
84         return list_entry(head, struct inode, i_wb_list);
85 }
86
87 /* Wakeup flusher thread or forker thread to fork it. Requires bdi->wb_lock. */
88 static void bdi_wakeup_flusher(struct backing_dev_info *bdi)
89 {
90         if (bdi->wb.task) {
91                 wake_up_process(bdi->wb.task);
92         } else {
93                 /*
94                  * The bdi thread isn't there, wake up the forker thread which
95                  * will create and run it.
96                  */
97                 wake_up_process(default_backing_dev_info.wb.task);
98         }
99 }
100
101 static void bdi_queue_work(struct backing_dev_info *bdi,
102                            struct wb_writeback_work *work)
103 {
104         trace_writeback_queue(bdi, work);
105
106         spin_lock_bh(&bdi->wb_lock);
107         list_add_tail(&work->list, &bdi->work_list);
108         if (!bdi->wb.task)
109                 trace_writeback_nothread(bdi, work);
110         bdi_wakeup_flusher(bdi);
111         spin_unlock_bh(&bdi->wb_lock);
112 }
113
114 static void
115 __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
116                       bool range_cyclic)
117 {
118         struct wb_writeback_work *work;
119
120         /*
121          * This is WB_SYNC_NONE writeback, so if allocation fails just
122          * wakeup the thread for old dirty data writeback
123          */
124         work = kzalloc(sizeof(*work), GFP_ATOMIC);
125         if (!work) {
126                 if (bdi->wb.task) {
127                         trace_writeback_nowork(bdi);
128                         wake_up_process(bdi->wb.task);
129                 }
130                 return;
131         }
132
133         work->sync_mode = WB_SYNC_NONE;
134         work->nr_pages  = nr_pages;
135         work->range_cyclic = range_cyclic;
136
137         bdi_queue_work(bdi, work);
138 }
139
140 /**
141  * bdi_start_writeback - start writeback
142  * @bdi: the backing device to write from
143  * @nr_pages: the number of pages to write
144  *
145  * Description:
146  *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
147  *   started when this function returns, we make no guarantees on
148  *   completion. Caller need not hold sb s_umount semaphore.
149  *
150  */
151 void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
152 {
153         __bdi_start_writeback(bdi, nr_pages, true);
154 }
155
156 /**
157  * bdi_start_background_writeback - start background writeback
158  * @bdi: the backing device to write from
159  *
160  * Description:
161  *   This makes sure WB_SYNC_NONE background writeback happens. When
162  *   this function returns, it is only guaranteed that for given BDI
163  *   some IO is happening if we are over background dirty threshold.
164  *   Caller need not hold sb s_umount semaphore.
165  */
166 void bdi_start_background_writeback(struct backing_dev_info *bdi)
167 {
168         /*
169          * We just wake up the flusher thread. It will perform background
170          * writeback as soon as there is no other work to do.
171          */
172         trace_writeback_wake_background(bdi);
173         spin_lock_bh(&bdi->wb_lock);
174         bdi_wakeup_flusher(bdi);
175         spin_unlock_bh(&bdi->wb_lock);
176 }
177
178 /*
179  * Remove the inode from the writeback list it is on.
180  */
181 void inode_wb_list_del(struct inode *inode)
182 {
183         spin_lock(&inode_wb_list_lock);
184         list_del_init(&inode->i_wb_list);
185         spin_unlock(&inode_wb_list_lock);
186 }
187
188
189 /*
190  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
191  * furthest end of its superblock's dirty-inode list.
192  *
193  * Before stamping the inode's ->dirtied_when, we check to see whether it is
194  * already the most-recently-dirtied inode on the b_dirty list.  If that is
195  * the case then the inode must have been redirtied while it was being written
196  * out and we don't reset its dirtied_when.
197  */
198 static void redirty_tail(struct inode *inode)
199 {
200         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
201
202         assert_spin_locked(&inode_wb_list_lock);
203         if (!list_empty(&wb->b_dirty)) {
204                 struct inode *tail;
205
206                 tail = wb_inode(wb->b_dirty.next);
207                 if (time_before(inode->dirtied_when, tail->dirtied_when))
208                         inode->dirtied_when = jiffies;
209         }
210         list_move(&inode->i_wb_list, &wb->b_dirty);
211 }
212
213 /*
214  * requeue inode for re-scanning after bdi->b_io list is exhausted.
215  */
216 static void requeue_io(struct inode *inode)
217 {
218         struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
219
220         assert_spin_locked(&inode_wb_list_lock);
221         list_move(&inode->i_wb_list, &wb->b_more_io);
222 }
223
224 static void inode_sync_complete(struct inode *inode)
225 {
226         /*
227          * Prevent speculative execution through
228          * spin_unlock(&inode_wb_list_lock);
229          */
230
231         smp_mb();
232         wake_up_bit(&inode->i_state, __I_SYNC);
233 }
234
235 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
236 {
237         bool ret = time_after(inode->dirtied_when, t);
238 #ifndef CONFIG_64BIT
239         /*
240          * For inodes being constantly redirtied, dirtied_when can get stuck.
241          * It _appears_ to be in the future, but is actually in distant past.
242          * This test is necessary to prevent such wrapped-around relative times
243          * from permanently stopping the whole bdi writeback.
244          */
245         ret = ret && time_before_eq(inode->dirtied_when, jiffies);
246 #endif
247         return ret;
248 }
249
250 /*
251  * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
252  */
253 static void move_expired_inodes(struct list_head *delaying_queue,
254                                struct list_head *dispatch_queue,
255                                 unsigned long *older_than_this)
256 {
257         LIST_HEAD(tmp);
258         struct list_head *pos, *node;
259         struct super_block *sb = NULL;
260         struct inode *inode;
261         int do_sb_sort = 0;
262
263         while (!list_empty(delaying_queue)) {
264                 inode = wb_inode(delaying_queue->prev);
265                 if (older_than_this &&
266                     inode_dirtied_after(inode, *older_than_this))
267                         break;
268                 if (sb && sb != inode->i_sb)
269                         do_sb_sort = 1;
270                 sb = inode->i_sb;
271                 list_move(&inode->i_wb_list, &tmp);
272         }
273
274         /* just one sb in list, splice to dispatch_queue and we're done */
275         if (!do_sb_sort) {
276                 list_splice(&tmp, dispatch_queue);
277                 return;
278         }
279
280         /* Move inodes from one superblock together */
281         while (!list_empty(&tmp)) {
282                 sb = wb_inode(tmp.prev)->i_sb;
283                 list_for_each_prev_safe(pos, node, &tmp) {
284                         inode = wb_inode(pos);
285                         if (inode->i_sb == sb)
286                                 list_move(&inode->i_wb_list, dispatch_queue);
287                 }
288         }
289 }
290
291 /*
292  * Queue all expired dirty inodes for io, eldest first.
293  * Before
294  *         newly dirtied     b_dirty    b_io    b_more_io
295  *         =============>    gf         edc     BA
296  * After
297  *         newly dirtied     b_dirty    b_io    b_more_io
298  *         =============>    g          fBAedc
299  *                                           |
300  *                                           +--> dequeue for IO
301  */
302 static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
303 {
304         assert_spin_locked(&inode_wb_list_lock);
305         list_splice_init(&wb->b_more_io, &wb->b_io);
306         move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
307 }
308
309 static int write_inode(struct inode *inode, struct writeback_control *wbc)
310 {
311         if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
312                 return inode->i_sb->s_op->write_inode(inode, wbc);
313         return 0;
314 }
315
316 /*
317  * Wait for writeback on an inode to complete.
318  */
319 static void inode_wait_for_writeback(struct inode *inode)
320 {
321         DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
322         wait_queue_head_t *wqh;
323
324         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
325         while (inode->i_state & I_SYNC) {
326                 spin_unlock(&inode->i_lock);
327                 spin_unlock(&inode_wb_list_lock);
328                 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
329                 spin_lock(&inode_wb_list_lock);
330                 spin_lock(&inode->i_lock);
331         }
332 }
333
334 /*
335  * Write out an inode's dirty pages.  Called under inode_wb_list_lock and
336  * inode->i_lock.  Either the caller has an active reference on the inode or
337  * the inode has I_WILL_FREE set.
338  *
339  * If `wait' is set, wait on the writeout.
340  *
341  * The whole writeout design is quite complex and fragile.  We want to avoid
342  * starvation of particular inodes when others are being redirtied, prevent
343  * livelocks, etc.
344  */
345 static int
346 writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
347 {
348         struct address_space *mapping = inode->i_mapping;
349         unsigned dirty;
350         int ret;
351
352         assert_spin_locked(&inode_wb_list_lock);
353         assert_spin_locked(&inode->i_lock);
354
355         if (!atomic_read(&inode->i_count))
356                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
357         else
358                 WARN_ON(inode->i_state & I_WILL_FREE);
359
360         if (inode->i_state & I_SYNC) {
361                 /*
362                  * If this inode is locked for writeback and we are not doing
363                  * writeback-for-data-integrity, move it to b_more_io so that
364                  * writeback can proceed with the other inodes on s_io.
365                  *
366                  * We'll have another go at writing back this inode when we
367                  * completed a full scan of b_io.
368                  */
369                 if (wbc->sync_mode != WB_SYNC_ALL) {
370                         requeue_io(inode);
371                         return 0;
372                 }
373
374                 /*
375                  * It's a data-integrity sync.  We must wait.
376                  */
377                 inode_wait_for_writeback(inode);
378         }
379
380         BUG_ON(inode->i_state & I_SYNC);
381
382         /* Set I_SYNC, reset I_DIRTY_PAGES */
383         inode->i_state |= I_SYNC;
384         inode->i_state &= ~I_DIRTY_PAGES;
385         spin_unlock(&inode->i_lock);
386         spin_unlock(&inode_wb_list_lock);
387
388         ret = do_writepages(mapping, wbc);
389
390         /*
391          * Make sure to wait on the data before writing out the metadata.
392          * This is important for filesystems that modify metadata on data
393          * I/O completion.
394          */
395         if (wbc->sync_mode == WB_SYNC_ALL) {
396                 int err = filemap_fdatawait(mapping);
397                 if (ret == 0)
398                         ret = err;
399         }
400
401         /*
402          * Some filesystems may redirty the inode during the writeback
403          * due to delalloc, clear dirty metadata flags right before
404          * write_inode()
405          */
406         spin_lock(&inode->i_lock);
407         dirty = inode->i_state & I_DIRTY;
408         inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
409         spin_unlock(&inode->i_lock);
410         /* Don't write the inode if only I_DIRTY_PAGES was set */
411         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
412                 int err = write_inode(inode, wbc);
413                 if (ret == 0)
414                         ret = err;
415         }
416
417         spin_lock(&inode_wb_list_lock);
418         spin_lock(&inode->i_lock);
419         inode->i_state &= ~I_SYNC;
420         if (!(inode->i_state & I_FREEING)) {
421                 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
422                         /*
423                          * We didn't write back all the pages.  nfs_writepages()
424                          * sometimes bales out without doing anything.
425                          */
426                         inode->i_state |= I_DIRTY_PAGES;
427                         if (wbc->nr_to_write <= 0) {
428                                 /*
429                                  * slice used up: queue for next turn
430                                  */
431                                 requeue_io(inode);
432                         } else {
433                                 /*
434                                  * Writeback blocked by something other than
435                                  * congestion. Delay the inode for some time to
436                                  * avoid spinning on the CPU (100% iowait)
437                                  * retrying writeback of the dirty page/inode
438                                  * that cannot be performed immediately.
439                                  */
440                                 redirty_tail(inode);
441                         }
442                 } else if (inode->i_state & I_DIRTY) {
443                         /*
444                          * Filesystems can dirty the inode during writeback
445                          * operations, such as delayed allocation during
446                          * submission or metadata updates after data IO
447                          * completion.
448                          */
449                         redirty_tail(inode);
450                 } else {
451                         /*
452                          * The inode is clean.  At this point we either have
453                          * a reference to the inode or it's on it's way out.
454                          * No need to add it back to the LRU.
455                          */
456                         list_del_init(&inode->i_wb_list);
457                 }
458         }
459         inode_sync_complete(inode);
460         return ret;
461 }
462
463 /*
464  * For background writeback the caller does not have the sb pinned
465  * before calling writeback. So make sure that we do pin it, so it doesn't
466  * go away while we are writing inodes from it.
467  */
468 static bool pin_sb_for_writeback(struct super_block *sb)
469 {
470         spin_lock(&sb_lock);
471         if (list_empty(&sb->s_instances)) {
472                 spin_unlock(&sb_lock);
473                 return false;
474         }
475
476         sb->s_count++;
477         spin_unlock(&sb_lock);
478
479         if (down_read_trylock(&sb->s_umount)) {
480                 if (sb->s_root)
481                         return true;
482                 up_read(&sb->s_umount);
483         }
484
485         put_super(sb);
486         return false;
487 }
488
489 /*
490  * Write a portion of b_io inodes which belong to @sb.
491  *
492  * If @only_this_sb is true, then find and write all such
493  * inodes. Otherwise write only ones which go sequentially
494  * in reverse order.
495  *
496  * Return 1, if the caller writeback routine should be
497  * interrupted. Otherwise return 0.
498  */
499 static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
500                 struct writeback_control *wbc, bool only_this_sb)
501 {
502         while (!list_empty(&wb->b_io)) {
503                 long pages_skipped;
504                 struct inode *inode = wb_inode(wb->b_io.prev);
505
506                 if (inode->i_sb != sb) {
507                         if (only_this_sb) {
508                                 /*
509                                  * We only want to write back data for this
510                                  * superblock, move all inodes not belonging
511                                  * to it back onto the dirty list.
512                                  */
513                                 redirty_tail(inode);
514                                 continue;
515                         }
516
517                         /*
518                          * The inode belongs to a different superblock.
519                          * Bounce back to the caller to unpin this and
520                          * pin the next superblock.
521                          */
522                         return 0;
523                 }
524
525                 /*
526                  * Don't bother with new inodes or inodes beeing freed, first
527                  * kind does not need peridic writeout yet, and for the latter
528                  * kind writeout is handled by the freer.
529                  */
530                 spin_lock(&inode->i_lock);
531                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
532                         spin_unlock(&inode->i_lock);
533                         requeue_io(inode);
534                         continue;
535                 }
536
537                 /*
538                  * Was this inode dirtied after sync_sb_inodes was called?
539                  * This keeps sync from extra jobs and livelock.
540                  */
541                 if (inode_dirtied_after(inode, wbc->wb_start)) {
542                         spin_unlock(&inode->i_lock);
543                         return 1;
544                 }
545
546                 __iget(inode);
547
548                 pages_skipped = wbc->pages_skipped;
549                 writeback_single_inode(inode, wbc);
550                 if (wbc->pages_skipped != pages_skipped) {
551                         /*
552                          * writeback is not making progress due to locked
553                          * buffers.  Skip this inode for now.
554                          */
555                         redirty_tail(inode);
556                 }
557                 spin_unlock(&inode->i_lock);
558                 spin_unlock(&inode_wb_list_lock);
559                 iput(inode);
560                 cond_resched();
561                 spin_lock(&inode_wb_list_lock);
562                 if (wbc->nr_to_write <= 0) {
563                         wbc->more_io = 1;
564                         return 1;
565                 }
566                 if (!list_empty(&wb->b_more_io))
567                         wbc->more_io = 1;
568         }
569         /* b_io is empty */
570         return 1;
571 }
572
573 void writeback_inodes_wb(struct bdi_writeback *wb,
574                 struct writeback_control *wbc)
575 {
576         int ret = 0;
577
578         if (!wbc->wb_start)
579                 wbc->wb_start = jiffies; /* livelock avoidance */
580         spin_lock(&inode_wb_list_lock);
581         if (!wbc->for_kupdate || list_empty(&wb->b_io))
582                 queue_io(wb, wbc->older_than_this);
583
584         while (!list_empty(&wb->b_io)) {
585                 struct inode *inode = wb_inode(wb->b_io.prev);
586                 struct super_block *sb = inode->i_sb;
587
588                 if (!pin_sb_for_writeback(sb)) {
589                         requeue_io(inode);
590                         continue;
591                 }
592                 ret = writeback_sb_inodes(sb, wb, wbc, false);
593                 drop_super(sb);
594
595                 if (ret)
596                         break;
597         }
598         spin_unlock(&inode_wb_list_lock);
599         /* Leave any unwritten inodes on b_io */
600 }
601
602 static void __writeback_inodes_sb(struct super_block *sb,
603                 struct bdi_writeback *wb, struct writeback_control *wbc)
604 {
605         WARN_ON(!rwsem_is_locked(&sb->s_umount));
606
607         spin_lock(&inode_wb_list_lock);
608         if (!wbc->for_kupdate || list_empty(&wb->b_io))
609                 queue_io(wb, wbc->older_than_this);
610         writeback_sb_inodes(sb, wb, wbc, true);
611         spin_unlock(&inode_wb_list_lock);
612 }
613
614 /*
615  * The maximum number of pages to writeout in a single bdi flush/kupdate
616  * operation.  We do this so we don't hold I_SYNC against an inode for
617  * enormous amounts of time, which would block a userspace task which has
618  * been forced to throttle against that inode.  Also, the code reevaluates
619  * the dirty each time it has written this many pages.
620  */
621 #define MAX_WRITEBACK_PAGES     1024
622
623 static inline bool over_bground_thresh(void)
624 {
625         unsigned long background_thresh, dirty_thresh;
626
627         global_dirty_limits(&background_thresh, &dirty_thresh);
628
629         return (global_page_state(NR_FILE_DIRTY) +
630                 global_page_state(NR_UNSTABLE_NFS) > background_thresh);
631 }
632
633 /*
634  * Explicit flushing or periodic writeback of "old" data.
635  *
636  * Define "old": the first time one of an inode's pages is dirtied, we mark the
637  * dirtying-time in the inode's address_space.  So this periodic writeback code
638  * just walks the superblock inode list, writing back any inodes which are
639  * older than a specific point in time.
640  *
641  * Try to run once per dirty_writeback_interval.  But if a writeback event
642  * takes longer than a dirty_writeback_interval interval, then leave a
643  * one-second gap.
644  *
645  * older_than_this takes precedence over nr_to_write.  So we'll only write back
646  * all dirty pages if they are all attached to "old" mappings.
647  */
648 static long wb_writeback(struct bdi_writeback *wb,
649                          struct wb_writeback_work *work)
650 {
651         struct writeback_control wbc = {
652                 .sync_mode              = work->sync_mode,
653                 .older_than_this        = NULL,
654                 .for_kupdate            = work->for_kupdate,
655                 .for_background         = work->for_background,
656                 .range_cyclic           = work->range_cyclic,
657         };
658         unsigned long oldest_jif;
659         long wrote = 0;
660         long write_chunk;
661         struct inode *inode;
662
663         if (wbc.for_kupdate) {
664                 wbc.older_than_this = &oldest_jif;
665                 oldest_jif = jiffies -
666                                 msecs_to_jiffies(dirty_expire_interval * 10);
667         }
668         if (!wbc.range_cyclic) {
669                 wbc.range_start = 0;
670                 wbc.range_end = LLONG_MAX;
671         }
672
673         /*
674          * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
675          * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
676          * here avoids calling into writeback_inodes_wb() more than once.
677          *
678          * The intended call sequence for WB_SYNC_ALL writeback is:
679          *
680          *      wb_writeback()
681          *          __writeback_inodes_sb()     <== called only once
682          *              write_cache_pages()     <== called once for each inode
683          *                   (quickly) tag currently dirty pages
684          *                   (maybe slowly) sync all tagged pages
685          */
686         if (wbc.sync_mode == WB_SYNC_NONE)
687                 write_chunk = MAX_WRITEBACK_PAGES;
688         else
689                 write_chunk = LONG_MAX;
690
691         wbc.wb_start = jiffies; /* livelock avoidance */
692         for (;;) {
693                 /*
694                  * Stop writeback when nr_pages has been consumed
695                  */
696                 if (work->nr_pages <= 0)
697                         break;
698
699                 /*
700                  * Background writeout and kupdate-style writeback may
701                  * run forever. Stop them if there is other work to do
702                  * so that e.g. sync can proceed. They'll be restarted
703                  * after the other works are all done.
704                  */
705                 if ((work->for_background || work->for_kupdate) &&
706                     !list_empty(&wb->bdi->work_list))
707                         break;
708
709                 /*
710                  * For background writeout, stop when we are below the
711                  * background dirty threshold
712                  */
713                 if (work->for_background && !over_bground_thresh())
714                         break;
715
716                 wbc.more_io = 0;
717                 wbc.nr_to_write = write_chunk;
718                 wbc.pages_skipped = 0;
719
720                 trace_wbc_writeback_start(&wbc, wb->bdi);
721                 if (work->sb)
722                         __writeback_inodes_sb(work->sb, wb, &wbc);
723                 else
724                         writeback_inodes_wb(wb, &wbc);
725                 trace_wbc_writeback_written(&wbc, wb->bdi);
726
727                 work->nr_pages -= write_chunk - wbc.nr_to_write;
728                 wrote += write_chunk - wbc.nr_to_write;
729
730                 /*
731                  * If we consumed everything, see if we have more
732                  */
733                 if (wbc.nr_to_write <= 0)
734                         continue;
735                 /*
736                  * Didn't write everything and we don't have more IO, bail
737                  */
738                 if (!wbc.more_io)
739                         break;
740                 /*
741                  * Did we write something? Try for more
742                  */
743                 if (wbc.nr_to_write < write_chunk)
744                         continue;
745                 /*
746                  * Nothing written. Wait for some inode to
747                  * become available for writeback. Otherwise
748                  * we'll just busyloop.
749                  */
750                 spin_lock(&inode_wb_list_lock);
751                 if (!list_empty(&wb->b_more_io))  {
752                         inode = wb_inode(wb->b_more_io.prev);
753                         trace_wbc_writeback_wait(&wbc, wb->bdi);
754                         spin_lock(&inode->i_lock);
755                         inode_wait_for_writeback(inode);
756                         spin_unlock(&inode->i_lock);
757                 }
758                 spin_unlock(&inode_wb_list_lock);
759         }
760
761         return wrote;
762 }
763
764 /*
765  * Return the next wb_writeback_work struct that hasn't been processed yet.
766  */
767 static struct wb_writeback_work *
768 get_next_work_item(struct backing_dev_info *bdi)
769 {
770         struct wb_writeback_work *work = NULL;
771
772         spin_lock_bh(&bdi->wb_lock);
773         if (!list_empty(&bdi->work_list)) {
774                 work = list_entry(bdi->work_list.next,
775                                   struct wb_writeback_work, list);
776                 list_del_init(&work->list);
777         }
778         spin_unlock_bh(&bdi->wb_lock);
779         return work;
780 }
781
782 /*
783  * Add in the number of potentially dirty inodes, because each inode
784  * write can dirty pagecache in the underlying blockdev.
785  */
786 static unsigned long get_nr_dirty_pages(void)
787 {
788         return global_page_state(NR_FILE_DIRTY) +
789                 global_page_state(NR_UNSTABLE_NFS) +
790                 get_nr_dirty_inodes();
791 }
792
793 static long wb_check_background_flush(struct bdi_writeback *wb)
794 {
795         if (over_bground_thresh()) {
796
797                 struct wb_writeback_work work = {
798                         .nr_pages       = LONG_MAX,
799                         .sync_mode      = WB_SYNC_NONE,
800                         .for_background = 1,
801                         .range_cyclic   = 1,
802                 };
803
804                 return wb_writeback(wb, &work);
805         }
806
807         return 0;
808 }
809
810 static long wb_check_old_data_flush(struct bdi_writeback *wb)
811 {
812         unsigned long expired;
813         long nr_pages;
814
815         /*
816          * When set to zero, disable periodic writeback
817          */
818         if (!dirty_writeback_interval)
819                 return 0;
820
821         expired = wb->last_old_flush +
822                         msecs_to_jiffies(dirty_writeback_interval * 10);
823         if (time_before(jiffies, expired))
824                 return 0;
825
826         wb->last_old_flush = jiffies;
827         nr_pages = get_nr_dirty_pages();
828
829         if (nr_pages) {
830                 struct wb_writeback_work work = {
831                         .nr_pages       = nr_pages,
832                         .sync_mode      = WB_SYNC_NONE,
833                         .for_kupdate    = 1,
834                         .range_cyclic   = 1,
835                 };
836
837                 return wb_writeback(wb, &work);
838         }
839
840         return 0;
841 }
842
843 /*
844  * Retrieve work items and do the writeback they describe
845  */
846 long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
847 {
848         struct backing_dev_info *bdi = wb->bdi;
849         struct wb_writeback_work *work;
850         long wrote = 0;
851
852         set_bit(BDI_writeback_running, &wb->bdi->state);
853         while ((work = get_next_work_item(bdi)) != NULL) {
854                 /*
855                  * Override sync mode, in case we must wait for completion
856                  * because this thread is exiting now.
857                  */
858                 if (force_wait)
859                         work->sync_mode = WB_SYNC_ALL;
860
861                 trace_writeback_exec(bdi, work);
862
863                 wrote += wb_writeback(wb, work);
864
865                 /*
866                  * Notify the caller of completion if this is a synchronous
867                  * work item, otherwise just free it.
868                  */
869                 if (work->done)
870                         complete(work->done);
871                 else
872                         kfree(work);
873         }
874
875         /*
876          * Check for periodic writeback, kupdated() style
877          */
878         wrote += wb_check_old_data_flush(wb);
879         wrote += wb_check_background_flush(wb);
880         clear_bit(BDI_writeback_running, &wb->bdi->state);
881
882         return wrote;
883 }
884
885 /*
886  * Handle writeback of dirty data for the device backed by this bdi. Also
887  * wakes up periodically and does kupdated style flushing.
888  */
889 int bdi_writeback_thread(void *data)
890 {
891         struct bdi_writeback *wb = data;
892         struct backing_dev_info *bdi = wb->bdi;
893         long pages_written;
894
895         current->flags |= PF_SWAPWRITE;
896         set_freezable();
897         wb->last_active = jiffies;
898
899         /*
900          * Our parent may run at a different priority, just set us to normal
901          */
902         set_user_nice(current, 0);
903
904         trace_writeback_thread_start(bdi);
905
906         while (!kthread_should_stop()) {
907                 /*
908                  * Remove own delayed wake-up timer, since we are already awake
909                  * and we'll take care of the preriodic write-back.
910                  */
911                 del_timer(&wb->wakeup_timer);
912
913                 pages_written = wb_do_writeback(wb, 0);
914
915                 trace_writeback_pages_written(pages_written);
916
917                 if (pages_written)
918                         wb->last_active = jiffies;
919
920                 set_current_state(TASK_INTERRUPTIBLE);
921                 if (!list_empty(&bdi->work_list) || kthread_should_stop()) {
922                         __set_current_state(TASK_RUNNING);
923                         continue;
924                 }
925
926                 if (wb_has_dirty_io(wb) && dirty_writeback_interval)
927                         schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
928                 else {
929                         /*
930                          * We have nothing to do, so can go sleep without any
931                          * timeout and save power. When a work is queued or
932                          * something is made dirty - we will be woken up.
933                          */
934                         schedule();
935                 }
936
937                 try_to_freeze();
938         }
939
940         /* Flush any work that raced with us exiting */
941         if (!list_empty(&bdi->work_list))
942                 wb_do_writeback(wb, 1);
943
944         trace_writeback_thread_stop(bdi);
945         return 0;
946 }
947
948
949 /*
950  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
951  * the whole world.
952  */
953 void wakeup_flusher_threads(long nr_pages)
954 {
955         struct backing_dev_info *bdi;
956
957         if (!nr_pages) {
958                 nr_pages = global_page_state(NR_FILE_DIRTY) +
959                                 global_page_state(NR_UNSTABLE_NFS);
960         }
961
962         rcu_read_lock();
963         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
964                 if (!bdi_has_dirty_io(bdi))
965                         continue;
966                 __bdi_start_writeback(bdi, nr_pages, false);
967         }
968         rcu_read_unlock();
969 }
970
971 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
972 {
973         if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
974                 struct dentry *dentry;
975                 const char *name = "?";
976
977                 dentry = d_find_alias(inode);
978                 if (dentry) {
979                         spin_lock(&dentry->d_lock);
980                         name = (const char *) dentry->d_name.name;
981                 }
982                 printk(KERN_DEBUG
983                        "%s(%d): dirtied inode %lu (%s) on %s\n",
984                        current->comm, task_pid_nr(current), inode->i_ino,
985                        name, inode->i_sb->s_id);
986                 if (dentry) {
987                         spin_unlock(&dentry->d_lock);
988                         dput(dentry);
989                 }
990         }
991 }
992
993 /**
994  *      __mark_inode_dirty -    internal function
995  *      @inode: inode to mark
996  *      @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
997  *      Mark an inode as dirty. Callers should use mark_inode_dirty or
998  *      mark_inode_dirty_sync.
999  *
1000  * Put the inode on the super block's dirty list.
1001  *
1002  * CAREFUL! We mark it dirty unconditionally, but move it onto the
1003  * dirty list only if it is hashed or if it refers to a blockdev.
1004  * If it was not hashed, it will never be added to the dirty list
1005  * even if it is later hashed, as it will have been marked dirty already.
1006  *
1007  * In short, make sure you hash any inodes _before_ you start marking
1008  * them dirty.
1009  *
1010  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
1011  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
1012  * the kernel-internal blockdev inode represents the dirtying time of the
1013  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
1014  * page->mapping->host, so the page-dirtying time is recorded in the internal
1015  * blockdev inode.
1016  */
1017 void __mark_inode_dirty(struct inode *inode, int flags)
1018 {
1019         struct super_block *sb = inode->i_sb;
1020         struct backing_dev_info *bdi = NULL;
1021
1022         /*
1023          * Don't do this for I_DIRTY_PAGES - that doesn't actually
1024          * dirty the inode itself
1025          */
1026         if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
1027                 if (sb->s_op->dirty_inode)
1028                         sb->s_op->dirty_inode(inode, flags);
1029         }
1030
1031         /*
1032          * make sure that changes are seen by all cpus before we test i_state
1033          * -- mikulas
1034          */
1035         smp_mb();
1036
1037         /* avoid the locking if we can */
1038         if ((inode->i_state & flags) == flags)
1039                 return;
1040
1041         if (unlikely(block_dump))
1042                 block_dump___mark_inode_dirty(inode);
1043
1044         spin_lock(&inode->i_lock);
1045         if ((inode->i_state & flags) != flags) {
1046                 const int was_dirty = inode->i_state & I_DIRTY;
1047
1048                 inode->i_state |= flags;
1049
1050                 /*
1051                  * If the inode is being synced, just update its dirty state.
1052                  * The unlocker will place the inode on the appropriate
1053                  * superblock list, based upon its state.
1054                  */
1055                 if (inode->i_state & I_SYNC)
1056                         goto out_unlock_inode;
1057
1058                 /*
1059                  * Only add valid (hashed) inodes to the superblock's
1060                  * dirty list.  Add blockdev inodes as well.
1061                  */
1062                 if (!S_ISBLK(inode->i_mode)) {
1063                         if (inode_unhashed(inode))
1064                                 goto out_unlock_inode;
1065                 }
1066                 if (inode->i_state & I_FREEING)
1067                         goto out_unlock_inode;
1068
1069                 /*
1070                  * If the inode was already on b_dirty/b_io/b_more_io, don't
1071                  * reposition it (that would break b_dirty time-ordering).
1072                  */
1073                 if (!was_dirty) {
1074                         bool wakeup_bdi = false;
1075                         bdi = inode_to_bdi(inode);
1076
1077                         if (bdi_cap_writeback_dirty(bdi)) {
1078                                 WARN(!test_bit(BDI_registered, &bdi->state),
1079                                      "bdi-%s not registered\n", bdi->name);
1080
1081                                 /*
1082                                  * If this is the first dirty inode for this
1083                                  * bdi, we have to wake-up the corresponding
1084                                  * bdi thread to make sure background
1085                                  * write-back happens later.
1086                                  */
1087                                 if (!wb_has_dirty_io(&bdi->wb))
1088                                         wakeup_bdi = true;
1089                         }
1090
1091                         spin_unlock(&inode->i_lock);
1092                         spin_lock(&inode_wb_list_lock);
1093                         inode->dirtied_when = jiffies;
1094                         list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
1095                         spin_unlock(&inode_wb_list_lock);
1096
1097                         if (wakeup_bdi)
1098                                 bdi_wakeup_thread_delayed(bdi);
1099                         return;
1100                 }
1101         }
1102 out_unlock_inode:
1103         spin_unlock(&inode->i_lock);
1104
1105 }
1106 EXPORT_SYMBOL(__mark_inode_dirty);
1107
1108 /*
1109  * Write out a superblock's list of dirty inodes.  A wait will be performed
1110  * upon no inodes, all inodes or the final one, depending upon sync_mode.
1111  *
1112  * If older_than_this is non-NULL, then only write out inodes which
1113  * had their first dirtying at a time earlier than *older_than_this.
1114  *
1115  * If `bdi' is non-zero then we're being asked to writeback a specific queue.
1116  * This function assumes that the blockdev superblock's inodes are backed by
1117  * a variety of queues, so all inodes are searched.  For other superblocks,
1118  * assume that all inodes are backed by the same queue.
1119  *
1120  * The inodes to be written are parked on bdi->b_io.  They are moved back onto
1121  * bdi->b_dirty as they are selected for writing.  This way, none can be missed
1122  * on the writer throttling path, and we get decent balancing between many
1123  * throttled threads: we don't want them all piling up on inode_sync_wait.
1124  */
1125 static void wait_sb_inodes(struct super_block *sb)
1126 {
1127         struct inode *inode, *old_inode = NULL;
1128
1129         /*
1130          * We need to be protected against the filesystem going from
1131          * r/o to r/w or vice versa.
1132          */
1133         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1134
1135         spin_lock(&inode_sb_list_lock);
1136
1137         /*
1138          * Data integrity sync. Must wait for all pages under writeback,
1139          * because there may have been pages dirtied before our sync
1140          * call, but which had writeout started before we write it out.
1141          * In which case, the inode may not be on the dirty list, but
1142          * we still have to wait for that writeout.
1143          */
1144         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
1145                 struct address_space *mapping = inode->i_mapping;
1146
1147                 spin_lock(&inode->i_lock);
1148                 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
1149                     (mapping->nrpages == 0)) {
1150                         spin_unlock(&inode->i_lock);
1151                         continue;
1152                 }
1153                 __iget(inode);
1154                 spin_unlock(&inode->i_lock);
1155                 spin_unlock(&inode_sb_list_lock);
1156
1157                 /*
1158                  * We hold a reference to 'inode' so it couldn't have been
1159                  * removed from s_inodes list while we dropped the
1160                  * inode_sb_list_lock.  We cannot iput the inode now as we can
1161                  * be holding the last reference and we cannot iput it under
1162                  * inode_sb_list_lock. So we keep the reference and iput it
1163                  * later.
1164                  */
1165                 iput(old_inode);
1166                 old_inode = inode;
1167
1168                 filemap_fdatawait(mapping);
1169
1170                 cond_resched();
1171
1172                 spin_lock(&inode_sb_list_lock);
1173         }
1174         spin_unlock(&inode_sb_list_lock);
1175         iput(old_inode);
1176 }
1177
1178 /**
1179  * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
1180  * @sb: the superblock
1181  * @nr: the number of pages to write
1182  *
1183  * Start writeback on some inodes on this super_block. No guarantees are made
1184  * on how many (if any) will be written, and this function does not wait
1185  * for IO completion of submitted IO.
1186  */
1187 void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr)
1188 {
1189         DECLARE_COMPLETION_ONSTACK(done);
1190         struct wb_writeback_work work = {
1191                 .sb             = sb,
1192                 .sync_mode      = WB_SYNC_NONE,
1193                 .done           = &done,
1194                 .nr_pages       = nr,
1195         };
1196
1197         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1198         bdi_queue_work(sb->s_bdi, &work);
1199         wait_for_completion(&done);
1200 }
1201 EXPORT_SYMBOL(writeback_inodes_sb_nr);
1202
1203 /**
1204  * writeback_inodes_sb  -       writeback dirty inodes from given super_block
1205  * @sb: the superblock
1206  *
1207  * Start writeback on some inodes on this super_block. No guarantees are made
1208  * on how many (if any) will be written, and this function does not wait
1209  * for IO completion of submitted IO.
1210  */
1211 void writeback_inodes_sb(struct super_block *sb)
1212 {
1213         return writeback_inodes_sb_nr(sb, get_nr_dirty_pages());
1214 }
1215 EXPORT_SYMBOL(writeback_inodes_sb);
1216
1217 /**
1218  * writeback_inodes_sb_if_idle  -       start writeback if none underway
1219  * @sb: the superblock
1220  *
1221  * Invoke writeback_inodes_sb if no writeback is currently underway.
1222  * Returns 1 if writeback was started, 0 if not.
1223  */
1224 int writeback_inodes_sb_if_idle(struct super_block *sb)
1225 {
1226         if (!writeback_in_progress(sb->s_bdi)) {
1227                 down_read(&sb->s_umount);
1228                 writeback_inodes_sb(sb);
1229                 up_read(&sb->s_umount);
1230                 return 1;
1231         } else
1232                 return 0;
1233 }
1234 EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
1235
1236 /**
1237  * writeback_inodes_sb_if_idle  -       start writeback if none underway
1238  * @sb: the superblock
1239  * @nr: the number of pages to write
1240  *
1241  * Invoke writeback_inodes_sb if no writeback is currently underway.
1242  * Returns 1 if writeback was started, 0 if not.
1243  */
1244 int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
1245                                    unsigned long nr)
1246 {
1247         if (!writeback_in_progress(sb->s_bdi)) {
1248                 down_read(&sb->s_umount);
1249                 writeback_inodes_sb_nr(sb, nr);
1250                 up_read(&sb->s_umount);
1251                 return 1;
1252         } else
1253                 return 0;
1254 }
1255 EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
1256
1257 /**
1258  * sync_inodes_sb       -       sync sb inode pages
1259  * @sb: the superblock
1260  *
1261  * This function writes and waits on any dirty inode belonging to this
1262  * super_block.
1263  */
1264 void sync_inodes_sb(struct super_block *sb)
1265 {
1266         DECLARE_COMPLETION_ONSTACK(done);
1267         struct wb_writeback_work work = {
1268                 .sb             = sb,
1269                 .sync_mode      = WB_SYNC_ALL,
1270                 .nr_pages       = LONG_MAX,
1271                 .range_cyclic   = 0,
1272                 .done           = &done,
1273         };
1274
1275         WARN_ON(!rwsem_is_locked(&sb->s_umount));
1276
1277         bdi_queue_work(sb->s_bdi, &work);
1278         wait_for_completion(&done);
1279
1280         wait_sb_inodes(sb);
1281 }
1282 EXPORT_SYMBOL(sync_inodes_sb);
1283
1284 /**
1285  * write_inode_now      -       write an inode to disk
1286  * @inode: inode to write to disk
1287  * @sync: whether the write should be synchronous or not
1288  *
1289  * This function commits an inode to disk immediately if it is dirty. This is
1290  * primarily needed by knfsd.
1291  *
1292  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
1293  */
1294 int write_inode_now(struct inode *inode, int sync)
1295 {
1296         int ret;
1297         struct writeback_control wbc = {
1298                 .nr_to_write = LONG_MAX,
1299                 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
1300                 .range_start = 0,
1301                 .range_end = LLONG_MAX,
1302         };
1303
1304         if (!mapping_cap_writeback_dirty(inode->i_mapping))
1305                 wbc.nr_to_write = 0;
1306
1307         might_sleep();
1308         spin_lock(&inode_wb_list_lock);
1309         spin_lock(&inode->i_lock);
1310         ret = writeback_single_inode(inode, &wbc);
1311         spin_unlock(&inode->i_lock);
1312         spin_unlock(&inode_wb_list_lock);
1313         if (sync)
1314                 inode_sync_wait(inode);
1315         return ret;
1316 }
1317 EXPORT_SYMBOL(write_inode_now);
1318
1319 /**
1320  * sync_inode - write an inode and its pages to disk.
1321  * @inode: the inode to sync
1322  * @wbc: controls the writeback mode
1323  *
1324  * sync_inode() will write an inode and its pages to disk.  It will also
1325  * correctly update the inode on its superblock's dirty inode lists and will
1326  * update inode->i_state.
1327  *
1328  * The caller must have a ref on the inode.
1329  */
1330 int sync_inode(struct inode *inode, struct writeback_control *wbc)
1331 {
1332         int ret;
1333
1334         spin_lock(&inode_wb_list_lock);
1335         spin_lock(&inode->i_lock);
1336         ret = writeback_single_inode(inode, wbc);
1337         spin_unlock(&inode->i_lock);
1338         spin_unlock(&inode_wb_list_lock);
1339         return ret;
1340 }
1341 EXPORT_SYMBOL(sync_inode);
1342
1343 /**
1344  * sync_inode_metadata - write an inode to disk
1345  * @inode: the inode to sync
1346  * @wait: wait for I/O to complete.
1347  *
1348  * Write an inode to disk and adjust its dirty state after completion.
1349  *
1350  * Note: only writes the actual inode, no associated data or other metadata.
1351  */
1352 int sync_inode_metadata(struct inode *inode, int wait)
1353 {
1354         struct writeback_control wbc = {
1355                 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
1356                 .nr_to_write = 0, /* metadata-only */
1357         };
1358
1359         return sync_inode(inode, &wbc);
1360 }
1361 EXPORT_SYMBOL(sync_inode_metadata);