xref: /openbmc/linux/fs/fs-writeback.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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	akpm@zip.com.au
12  *		Split out of fs/inode.c
13  *		Additions for address_space-based writeback
14  */
15 
16 #include <linux/kernel.h>
17 #include <linux/spinlock.h>
18 #include <linux/sched.h>
19 #include <linux/fs.h>
20 #include <linux/mm.h>
21 #include <linux/writeback.h>
22 #include <linux/blkdev.h>
23 #include <linux/backing-dev.h>
24 #include <linux/buffer_head.h>
25 #include "internal.h"
26 
27 /**
28  *	__mark_inode_dirty -	internal function
29  *	@inode: inode to mark
30  *	@flags: what kind of dirty (i.e. I_DIRTY_SYNC)
31  *	Mark an inode as dirty. Callers should use mark_inode_dirty or
32  *  	mark_inode_dirty_sync.
33  *
34  * Put the inode on the super block's dirty list.
35  *
36  * CAREFUL! We mark it dirty unconditionally, but move it onto the
37  * dirty list only if it is hashed or if it refers to a blockdev.
38  * If it was not hashed, it will never be added to the dirty list
39  * even if it is later hashed, as it will have been marked dirty already.
40  *
41  * In short, make sure you hash any inodes _before_ you start marking
42  * them dirty.
43  *
44  * This function *must* be atomic for the I_DIRTY_PAGES case -
45  * set_page_dirty() is called under spinlock in several places.
46  *
47  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
48  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
49  * the kernel-internal blockdev inode represents the dirtying time of the
50  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
51  * page->mapping->host, so the page-dirtying time is recorded in the internal
52  * blockdev inode.
53  */
54 void __mark_inode_dirty(struct inode *inode, int flags)
55 {
56 	struct super_block *sb = inode->i_sb;
57 
58 	/*
59 	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
60 	 * dirty the inode itself
61 	 */
62 	if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
63 		if (sb->s_op->dirty_inode)
64 			sb->s_op->dirty_inode(inode);
65 	}
66 
67 	/*
68 	 * make sure that changes are seen by all cpus before we test i_state
69 	 * -- mikulas
70 	 */
71 	smp_mb();
72 
73 	/* avoid the locking if we can */
74 	if ((inode->i_state & flags) == flags)
75 		return;
76 
77 	if (unlikely(block_dump)) {
78 		struct dentry *dentry = NULL;
79 		const char *name = "?";
80 
81 		if (!list_empty(&inode->i_dentry)) {
82 			dentry = list_entry(inode->i_dentry.next,
83 					    struct dentry, d_alias);
84 			if (dentry && dentry->d_name.name)
85 				name = (const char *) dentry->d_name.name;
86 		}
87 
88 		if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev"))
89 			printk(KERN_DEBUG
90 			       "%s(%d): dirtied inode %lu (%s) on %s\n",
91 			       current->comm, current->pid, inode->i_ino,
92 			       name, inode->i_sb->s_id);
93 	}
94 
95 	spin_lock(&inode_lock);
96 	if ((inode->i_state & flags) != flags) {
97 		const int was_dirty = inode->i_state & I_DIRTY;
98 
99 		inode->i_state |= flags;
100 
101 		/*
102 		 * If the inode is locked, just update its dirty state.
103 		 * The unlocker will place the inode on the appropriate
104 		 * superblock list, based upon its state.
105 		 */
106 		if (inode->i_state & I_LOCK)
107 			goto out;
108 
109 		/*
110 		 * Only add valid (hashed) inodes to the superblock's
111 		 * dirty list.  Add blockdev inodes as well.
112 		 */
113 		if (!S_ISBLK(inode->i_mode)) {
114 			if (hlist_unhashed(&inode->i_hash))
115 				goto out;
116 		}
117 		if (inode->i_state & (I_FREEING|I_CLEAR))
118 			goto out;
119 
120 		/*
121 		 * If the inode was already on s_dirty or s_io, don't
122 		 * reposition it (that would break s_dirty time-ordering).
123 		 */
124 		if (!was_dirty) {
125 			inode->dirtied_when = jiffies;
126 			list_move(&inode->i_list, &sb->s_dirty);
127 		}
128 	}
129 out:
130 	spin_unlock(&inode_lock);
131 }
132 
133 EXPORT_SYMBOL(__mark_inode_dirty);
134 
135 static int write_inode(struct inode *inode, int sync)
136 {
137 	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode))
138 		return inode->i_sb->s_op->write_inode(inode, sync);
139 	return 0;
140 }
141 
142 /*
143  * Write a single inode's dirty pages and inode data out to disk.
144  * If `wait' is set, wait on the writeout.
145  *
146  * The whole writeout design is quite complex and fragile.  We want to avoid
147  * starvation of particular inodes when others are being redirtied, prevent
148  * livelocks, etc.
149  *
150  * Called under inode_lock.
151  */
152 static int
153 __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
154 {
155 	unsigned dirty;
156 	struct address_space *mapping = inode->i_mapping;
157 	struct super_block *sb = inode->i_sb;
158 	int wait = wbc->sync_mode == WB_SYNC_ALL;
159 	int ret;
160 
161 	BUG_ON(inode->i_state & I_LOCK);
162 
163 	/* Set I_LOCK, reset I_DIRTY */
164 	dirty = inode->i_state & I_DIRTY;
165 	inode->i_state |= I_LOCK;
166 	inode->i_state &= ~I_DIRTY;
167 
168 	spin_unlock(&inode_lock);
169 
170 	ret = do_writepages(mapping, wbc);
171 
172 	/* Don't write the inode if only I_DIRTY_PAGES was set */
173 	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
174 		int err = write_inode(inode, wait);
175 		if (ret == 0)
176 			ret = err;
177 	}
178 
179 	if (wait) {
180 		int err = filemap_fdatawait(mapping);
181 		if (ret == 0)
182 			ret = err;
183 	}
184 
185 	spin_lock(&inode_lock);
186 	inode->i_state &= ~I_LOCK;
187 	if (!(inode->i_state & I_FREEING)) {
188 		if (!(inode->i_state & I_DIRTY) &&
189 		    mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
190 			/*
191 			 * We didn't write back all the pages.  nfs_writepages()
192 			 * sometimes bales out without doing anything. Redirty
193 			 * the inode.  It is still on sb->s_io.
194 			 */
195 			if (wbc->for_kupdate) {
196 				/*
197 				 * For the kupdate function we leave the inode
198 				 * at the head of sb_dirty so it will get more
199 				 * writeout as soon as the queue becomes
200 				 * uncongested.
201 				 */
202 				inode->i_state |= I_DIRTY_PAGES;
203 				list_move_tail(&inode->i_list, &sb->s_dirty);
204 			} else {
205 				/*
206 				 * Otherwise fully redirty the inode so that
207 				 * other inodes on this superblock will get some
208 				 * writeout.  Otherwise heavy writing to one
209 				 * file would indefinitely suspend writeout of
210 				 * all the other files.
211 				 */
212 				inode->i_state |= I_DIRTY_PAGES;
213 				inode->dirtied_when = jiffies;
214 				list_move(&inode->i_list, &sb->s_dirty);
215 			}
216 		} else if (inode->i_state & I_DIRTY) {
217 			/*
218 			 * Someone redirtied the inode while were writing back
219 			 * the pages.
220 			 */
221 			list_move(&inode->i_list, &sb->s_dirty);
222 		} else if (atomic_read(&inode->i_count)) {
223 			/*
224 			 * The inode is clean, inuse
225 			 */
226 			list_move(&inode->i_list, &inode_in_use);
227 		} else {
228 			/*
229 			 * The inode is clean, unused
230 			 */
231 			list_move(&inode->i_list, &inode_unused);
232 		}
233 	}
234 	wake_up_inode(inode);
235 	return ret;
236 }
237 
238 /*
239  * Write out an inode's dirty pages.  Called under inode_lock.  Either the
240  * caller has ref on the inode (either via __iget or via syscall against an fd)
241  * or the inode has I_WILL_FREE set (via generic_forget_inode)
242  */
243 static int
244 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
245 {
246 	wait_queue_head_t *wqh;
247 
248 	if (!atomic_read(&inode->i_count))
249 		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
250 	else
251 		WARN_ON(inode->i_state & I_WILL_FREE);
252 
253 	if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_LOCK)) {
254 		struct address_space *mapping = inode->i_mapping;
255 		int ret;
256 
257 		list_move(&inode->i_list, &inode->i_sb->s_dirty);
258 
259 		/*
260 		 * Even if we don't actually write the inode itself here,
261 		 * we can at least start some of the data writeout..
262 		 */
263 		spin_unlock(&inode_lock);
264 		ret = do_writepages(mapping, wbc);
265 		spin_lock(&inode_lock);
266 		return ret;
267 	}
268 
269 	/*
270 	 * It's a data-integrity sync.  We must wait.
271 	 */
272 	if (inode->i_state & I_LOCK) {
273 		DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LOCK);
274 
275 		wqh = bit_waitqueue(&inode->i_state, __I_LOCK);
276 		do {
277 			spin_unlock(&inode_lock);
278 			__wait_on_bit(wqh, &wq, inode_wait,
279 							TASK_UNINTERRUPTIBLE);
280 			spin_lock(&inode_lock);
281 		} while (inode->i_state & I_LOCK);
282 	}
283 	return __sync_single_inode(inode, wbc);
284 }
285 
286 /*
287  * Write out a superblock's list of dirty inodes.  A wait will be performed
288  * upon no inodes, all inodes or the final one, depending upon sync_mode.
289  *
290  * If older_than_this is non-NULL, then only write out inodes which
291  * had their first dirtying at a time earlier than *older_than_this.
292  *
293  * If we're a pdlfush thread, then implement pdflush collision avoidance
294  * against the entire list.
295  *
296  * WB_SYNC_HOLD is a hack for sys_sync(): reattach the inode to sb->s_dirty so
297  * that it can be located for waiting on in __writeback_single_inode().
298  *
299  * Called under inode_lock.
300  *
301  * If `bdi' is non-zero then we're being asked to writeback a specific queue.
302  * This function assumes that the blockdev superblock's inodes are backed by
303  * a variety of queues, so all inodes are searched.  For other superblocks,
304  * assume that all inodes are backed by the same queue.
305  *
306  * FIXME: this linear search could get expensive with many fileystems.  But
307  * how to fix?  We need to go from an address_space to all inodes which share
308  * a queue with that address_space.  (Easy: have a global "dirty superblocks"
309  * list).
310  *
311  * The inodes to be written are parked on sb->s_io.  They are moved back onto
312  * sb->s_dirty as they are selected for writing.  This way, none can be missed
313  * on the writer throttling path, and we get decent balancing between many
314  * throttled threads: we don't want them all piling up on __wait_on_inode.
315  */
316 static void
317 sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
318 {
319 	const unsigned long start = jiffies;	/* livelock avoidance */
320 
321 	if (!wbc->for_kupdate || list_empty(&sb->s_io))
322 		list_splice_init(&sb->s_dirty, &sb->s_io);
323 
324 	while (!list_empty(&sb->s_io)) {
325 		struct inode *inode = list_entry(sb->s_io.prev,
326 						struct inode, i_list);
327 		struct address_space *mapping = inode->i_mapping;
328 		struct backing_dev_info *bdi = mapping->backing_dev_info;
329 		long pages_skipped;
330 
331 		if (!bdi_cap_writeback_dirty(bdi)) {
332 			list_move(&inode->i_list, &sb->s_dirty);
333 			if (sb_is_blkdev_sb(sb)) {
334 				/*
335 				 * Dirty memory-backed blockdev: the ramdisk
336 				 * driver does this.  Skip just this inode
337 				 */
338 				continue;
339 			}
340 			/*
341 			 * Dirty memory-backed inode against a filesystem other
342 			 * than the kernel-internal bdev filesystem.  Skip the
343 			 * entire superblock.
344 			 */
345 			break;
346 		}
347 
348 		if (wbc->nonblocking && bdi_write_congested(bdi)) {
349 			wbc->encountered_congestion = 1;
350 			if (!sb_is_blkdev_sb(sb))
351 				break;		/* Skip a congested fs */
352 			list_move(&inode->i_list, &sb->s_dirty);
353 			continue;		/* Skip a congested blockdev */
354 		}
355 
356 		if (wbc->bdi && bdi != wbc->bdi) {
357 			if (!sb_is_blkdev_sb(sb))
358 				break;		/* fs has the wrong queue */
359 			list_move(&inode->i_list, &sb->s_dirty);
360 			continue;		/* blockdev has wrong queue */
361 		}
362 
363 		/* Was this inode dirtied after sync_sb_inodes was called? */
364 		if (time_after(inode->dirtied_when, start))
365 			break;
366 
367 		/* Was this inode dirtied too recently? */
368 		if (wbc->older_than_this && time_after(inode->dirtied_when,
369 						*wbc->older_than_this))
370 			break;
371 
372 		/* Is another pdflush already flushing this queue? */
373 		if (current_is_pdflush() && !writeback_acquire(bdi))
374 			break;
375 
376 		BUG_ON(inode->i_state & I_FREEING);
377 		__iget(inode);
378 		pages_skipped = wbc->pages_skipped;
379 		__writeback_single_inode(inode, wbc);
380 		if (wbc->sync_mode == WB_SYNC_HOLD) {
381 			inode->dirtied_when = jiffies;
382 			list_move(&inode->i_list, &sb->s_dirty);
383 		}
384 		if (current_is_pdflush())
385 			writeback_release(bdi);
386 		if (wbc->pages_skipped != pages_skipped) {
387 			/*
388 			 * writeback is not making progress due to locked
389 			 * buffers.  Skip this inode for now.
390 			 */
391 			list_move(&inode->i_list, &sb->s_dirty);
392 		}
393 		spin_unlock(&inode_lock);
394 		iput(inode);
395 		cond_resched();
396 		spin_lock(&inode_lock);
397 		if (wbc->nr_to_write <= 0)
398 			break;
399 	}
400 	return;		/* Leave any unwritten inodes on s_io */
401 }
402 
403 /*
404  * Start writeback of dirty pagecache data against all unlocked inodes.
405  *
406  * Note:
407  * We don't need to grab a reference to superblock here. If it has non-empty
408  * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
409  * past sync_inodes_sb() until both the ->s_dirty and ->s_io lists are
410  * empty. Since __sync_single_inode() regains inode_lock before it finally moves
411  * inode from superblock lists we are OK.
412  *
413  * If `older_than_this' is non-zero then only flush inodes which have a
414  * flushtime older than *older_than_this.
415  *
416  * If `bdi' is non-zero then we will scan the first inode against each
417  * superblock until we find the matching ones.  One group will be the dirty
418  * inodes against a filesystem.  Then when we hit the dummy blockdev superblock,
419  * sync_sb_inodes will seekout the blockdev which matches `bdi'.  Maybe not
420  * super-efficient but we're about to do a ton of I/O...
421  */
422 void
423 writeback_inodes(struct writeback_control *wbc)
424 {
425 	struct super_block *sb;
426 
427 	might_sleep();
428 	spin_lock(&sb_lock);
429 restart:
430 	sb = sb_entry(super_blocks.prev);
431 	for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
432 		if (!list_empty(&sb->s_dirty) || !list_empty(&sb->s_io)) {
433 			/* we're making our own get_super here */
434 			sb->s_count++;
435 			spin_unlock(&sb_lock);
436 			/*
437 			 * If we can't get the readlock, there's no sense in
438 			 * waiting around, most of the time the FS is going to
439 			 * be unmounted by the time it is released.
440 			 */
441 			if (down_read_trylock(&sb->s_umount)) {
442 				if (sb->s_root) {
443 					spin_lock(&inode_lock);
444 					sync_sb_inodes(sb, wbc);
445 					spin_unlock(&inode_lock);
446 				}
447 				up_read(&sb->s_umount);
448 			}
449 			spin_lock(&sb_lock);
450 			if (__put_super_and_need_restart(sb))
451 				goto restart;
452 		}
453 		if (wbc->nr_to_write <= 0)
454 			break;
455 	}
456 	spin_unlock(&sb_lock);
457 }
458 
459 /*
460  * writeback and wait upon the filesystem's dirty inodes.  The caller will
461  * do this in two passes - one to write, and one to wait.  WB_SYNC_HOLD is
462  * used to park the written inodes on sb->s_dirty for the wait pass.
463  *
464  * A finite limit is set on the number of pages which will be written.
465  * To prevent infinite livelock of sys_sync().
466  *
467  * We add in the number of potentially dirty inodes, because each inode write
468  * can dirty pagecache in the underlying blockdev.
469  */
470 void sync_inodes_sb(struct super_block *sb, int wait)
471 {
472 	struct writeback_control wbc = {
473 		.sync_mode	= wait ? WB_SYNC_ALL : WB_SYNC_HOLD,
474 		.range_start	= 0,
475 		.range_end	= LLONG_MAX,
476 	};
477 	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
478 	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
479 
480 	wbc.nr_to_write = nr_dirty + nr_unstable +
481 			(inodes_stat.nr_inodes - inodes_stat.nr_unused) +
482 			nr_dirty + nr_unstable;
483 	wbc.nr_to_write += wbc.nr_to_write / 2;		/* Bit more for luck */
484 	spin_lock(&inode_lock);
485 	sync_sb_inodes(sb, &wbc);
486 	spin_unlock(&inode_lock);
487 }
488 
489 /*
490  * Rather lame livelock avoidance.
491  */
492 static void set_sb_syncing(int val)
493 {
494 	struct super_block *sb;
495 	spin_lock(&sb_lock);
496 	sb = sb_entry(super_blocks.prev);
497 	for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
498 		sb->s_syncing = val;
499 	}
500 	spin_unlock(&sb_lock);
501 }
502 
503 /**
504  * sync_inodes - writes all inodes to disk
505  * @wait: wait for completion
506  *
507  * sync_inodes() goes through each super block's dirty inode list, writes the
508  * inodes out, waits on the writeout and puts the inodes back on the normal
509  * list.
510  *
511  * This is for sys_sync().  fsync_dev() uses the same algorithm.  The subtle
512  * part of the sync functions is that the blockdev "superblock" is processed
513  * last.  This is because the write_inode() function of a typical fs will
514  * perform no I/O, but will mark buffers in the blockdev mapping as dirty.
515  * What we want to do is to perform all that dirtying first, and then write
516  * back all those inode blocks via the blockdev mapping in one sweep.  So the
517  * additional (somewhat redundant) sync_blockdev() calls here are to make
518  * sure that really happens.  Because if we call sync_inodes_sb(wait=1) with
519  * outstanding dirty inodes, the writeback goes block-at-a-time within the
520  * filesystem's write_inode().  This is extremely slow.
521  */
522 static void __sync_inodes(int wait)
523 {
524 	struct super_block *sb;
525 
526 	spin_lock(&sb_lock);
527 restart:
528 	list_for_each_entry(sb, &super_blocks, s_list) {
529 		if (sb->s_syncing)
530 			continue;
531 		sb->s_syncing = 1;
532 		sb->s_count++;
533 		spin_unlock(&sb_lock);
534 		down_read(&sb->s_umount);
535 		if (sb->s_root) {
536 			sync_inodes_sb(sb, wait);
537 			sync_blockdev(sb->s_bdev);
538 		}
539 		up_read(&sb->s_umount);
540 		spin_lock(&sb_lock);
541 		if (__put_super_and_need_restart(sb))
542 			goto restart;
543 	}
544 	spin_unlock(&sb_lock);
545 }
546 
547 void sync_inodes(int wait)
548 {
549 	set_sb_syncing(0);
550 	__sync_inodes(0);
551 
552 	if (wait) {
553 		set_sb_syncing(0);
554 		__sync_inodes(1);
555 	}
556 }
557 
558 /**
559  * write_inode_now	-	write an inode to disk
560  * @inode: inode to write to disk
561  * @sync: whether the write should be synchronous or not
562  *
563  * This function commits an inode to disk immediately if it is dirty. This is
564  * primarily needed by knfsd.
565  *
566  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
567  */
568 int write_inode_now(struct inode *inode, int sync)
569 {
570 	int ret;
571 	struct writeback_control wbc = {
572 		.nr_to_write = LONG_MAX,
573 		.sync_mode = WB_SYNC_ALL,
574 		.range_start = 0,
575 		.range_end = LLONG_MAX,
576 	};
577 
578 	if (!mapping_cap_writeback_dirty(inode->i_mapping))
579 		wbc.nr_to_write = 0;
580 
581 	might_sleep();
582 	spin_lock(&inode_lock);
583 	ret = __writeback_single_inode(inode, &wbc);
584 	spin_unlock(&inode_lock);
585 	if (sync)
586 		wait_on_inode(inode);
587 	return ret;
588 }
589 EXPORT_SYMBOL(write_inode_now);
590 
591 /**
592  * sync_inode - write an inode and its pages to disk.
593  * @inode: the inode to sync
594  * @wbc: controls the writeback mode
595  *
596  * sync_inode() will write an inode and its pages to disk.  It will also
597  * correctly update the inode on its superblock's dirty inode lists and will
598  * update inode->i_state.
599  *
600  * The caller must have a ref on the inode.
601  */
602 int sync_inode(struct inode *inode, struct writeback_control *wbc)
603 {
604 	int ret;
605 
606 	spin_lock(&inode_lock);
607 	ret = __writeback_single_inode(inode, wbc);
608 	spin_unlock(&inode_lock);
609 	return ret;
610 }
611 EXPORT_SYMBOL(sync_inode);
612 
613 /**
614  * generic_osync_inode - flush all dirty data for a given inode to disk
615  * @inode: inode to write
616  * @mapping: the address_space that should be flushed
617  * @what:  what to write and wait upon
618  *
619  * This can be called by file_write functions for files which have the
620  * O_SYNC flag set, to flush dirty writes to disk.
621  *
622  * @what is a bitmask, specifying which part of the inode's data should be
623  * written and waited upon.
624  *
625  *    OSYNC_DATA:     i_mapping's dirty data
626  *    OSYNC_METADATA: the buffers at i_mapping->private_list
627  *    OSYNC_INODE:    the inode itself
628  */
629 
630 int generic_osync_inode(struct inode *inode, struct address_space *mapping, int what)
631 {
632 	int err = 0;
633 	int need_write_inode_now = 0;
634 	int err2;
635 
636 	if (what & OSYNC_DATA)
637 		err = filemap_fdatawrite(mapping);
638 	if (what & (OSYNC_METADATA|OSYNC_DATA)) {
639 		err2 = sync_mapping_buffers(mapping);
640 		if (!err)
641 			err = err2;
642 	}
643 	if (what & OSYNC_DATA) {
644 		err2 = filemap_fdatawait(mapping);
645 		if (!err)
646 			err = err2;
647 	}
648 
649 	spin_lock(&inode_lock);
650 	if ((inode->i_state & I_DIRTY) &&
651 	    ((what & OSYNC_INODE) || (inode->i_state & I_DIRTY_DATASYNC)))
652 		need_write_inode_now = 1;
653 	spin_unlock(&inode_lock);
654 
655 	if (need_write_inode_now) {
656 		err2 = write_inode_now(inode, 1);
657 		if (!err)
658 			err = err2;
659 	}
660 	else
661 		wait_on_inode(inode);
662 
663 	return err;
664 }
665 
666 EXPORT_SYMBOL(generic_osync_inode);
667 
668 /**
669  * writeback_acquire: attempt to get exclusive writeback access to a device
670  * @bdi: the device's backing_dev_info structure
671  *
672  * It is a waste of resources to have more than one pdflush thread blocked on
673  * a single request queue.  Exclusion at the request_queue level is obtained
674  * via a flag in the request_queue's backing_dev_info.state.
675  *
676  * Non-request_queue-backed address_spaces will share default_backing_dev_info,
677  * unless they implement their own.  Which is somewhat inefficient, as this
678  * may prevent concurrent writeback against multiple devices.
679  */
680 int writeback_acquire(struct backing_dev_info *bdi)
681 {
682 	return !test_and_set_bit(BDI_pdflush, &bdi->state);
683 }
684 
685 /**
686  * writeback_in_progress: determine whether there is writeback in progress
687  * @bdi: the device's backing_dev_info structure.
688  *
689  * Determine whether there is writeback in progress against a backing device.
690  */
691 int writeback_in_progress(struct backing_dev_info *bdi)
692 {
693 	return test_bit(BDI_pdflush, &bdi->state);
694 }
695 
696 /**
697  * writeback_release: relinquish exclusive writeback access against a device.
698  * @bdi: the device's backing_dev_info structure
699  */
700 void writeback_release(struct backing_dev_info *bdi)
701 {
702 	BUG_ON(!writeback_in_progress(bdi));
703 	clear_bit(BDI_pdflush, &bdi->state);
704 }
705