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Commit 5cee5815 authored by Jan Kara's avatar Jan Kara Committed by Al Viro
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vfs: Make sys_sync() use fsync_super() (version 4) 



It is unnecessarily fragile to have two places (fsync_super() and do_sync())
doing data integrity sync of the filesystem. Alter __fsync_super() to
accommodate needs of both callers and use it. So after this patch
__fsync_super() is the only place where we gather all the calls needed to
properly send all data on a filesystem to disk.

Nice bonus is that we get a complete livelock avoidance and write_supers()
is now only used for periodic writeback of superblocks.

sync_blockdevs() introduced a couple of patches ago is gone now.

[build fixes folded]

Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 429479f0

fs/block_dev.c

+10 −5
Original line number Diff line number Diff line
@@ -176,17 +176,22 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, 
				iov, offset, nr_segs, blkdev_get_blocks, NULL);

}



int __sync_blockdev(struct block_device *bdev, int wait)

{

	if (!bdev)

		return 0;

	if (!wait)

		return filemap_flush(bdev->bd_inode->i_mapping);

	return filemap_write_and_wait(bdev->bd_inode->i_mapping);

}



/*

 * Write out and wait upon all the dirty data associated with a block

 * device via its mapping.  Does not take the superblock lock.

 */

int sync_blockdev(struct block_device *bdev)

{

	int ret = 0;



	if (bdev)

		ret = filemap_write_and_wait(bdev->bd_inode->i_mapping);

	return ret;

	return __sync_blockdev(bdev, 1);

}

EXPORT_SYMBOL(sync_blockdev);

fs/fs-writeback.c

+0 −49
Original line number Diff line number Diff line
@@ -678,55 +678,6 @@ void sync_inodes_sb(struct super_block *sb, int wait) 
	sync_sb_inodes(sb, &wbc);

}



/**

 * sync_inodes - writes all inodes to disk

 * @wait: wait for completion

 *

 * sync_inodes() goes through each super block's dirty inode list, writes the

 * inodes out, waits on the writeout and puts the inodes back on the normal

 * list.

 *

 * This is for sys_sync().  fsync_dev() uses the same algorithm.  The subtle

 * part of the sync functions is that the blockdev "superblock" is processed

 * last.  This is because the write_inode() function of a typical fs will

 * perform no I/O, but will mark buffers in the blockdev mapping as dirty.

 * What we want to do is to perform all that dirtying first, and then write

 * back all those inode blocks via the blockdev mapping in one sweep.  So the

 * additional (somewhat redundant) sync_blockdev() calls here are to make

 * sure that really happens.  Because if we call sync_inodes_sb(wait=1) with

 * outstanding dirty inodes, the writeback goes block-at-a-time within the

 * filesystem's write_inode().  This is extremely slow.

 */

static void __sync_inodes(int wait)

{

	struct super_block *sb;



	spin_lock(&sb_lock);

restart:

	list_for_each_entry(sb, &super_blocks, s_list) {

		sb->s_count++;

		spin_unlock(&sb_lock);

		down_read(&sb->s_umount);

		if (sb->s_root) {

			sync_inodes_sb(sb, wait);

			sync_blockdev(sb->s_bdev);

		}

		up_read(&sb->s_umount);

		spin_lock(&sb_lock);

		if (__put_super_and_need_restart(sb))

			goto restart;

	}

	spin_unlock(&sb_lock);

}



void sync_inodes(int wait)

{

	__sync_inodes(0);



	if (wait)

		__sync_inodes(1);

}



/**

 * write_inode_now	-	write an inode to disk

 * @inode: inode to write to disk

fs/internal.h

+7 −9
Original line number Diff line number Diff line
@@ -25,6 +25,8 @@ static inline int sb_is_blkdev_sb(struct super_block *sb) 
	return sb == blockdev_superblock;

}



extern int __sync_blockdev(struct block_device *bdev, int wait);



#else

static inline void bdev_cache_init(void)

{
@@ -34,6 +36,11 @@ static inline int sb_is_blkdev_sb(struct super_block *sb) 
{

	return 0;

}



static inline int __sync_blockdev(struct block_device *bdev, int wait)

{

	return 0;

}

#endif



/*
@@ -71,12 +78,3 @@ extern void chroot_fs_refs(struct path *, struct path *); 
 * file_table.c

 */

extern void mark_files_ro(struct super_block *);
 


/*

 * super.c

 */

#ifdef CONFIG_BLOCK

extern void sync_blockdevs(void);

#else

static inline void sync_blockdevs(void) { }

#endif

fs/super.c

+23 −49
Original line number Diff line number Diff line
@@ -284,23 +284,23 @@ EXPORT_SYMBOL(lock_super); 
EXPORT_SYMBOL(unlock_super);



/*

 * Write out and wait upon all dirty data associated with this

 * superblock.  Filesystem data as well as the underlying block

 * device.  Takes the superblock lock.  Requires a second blkdev

 * flush by the caller to complete the operation.

 * Do the filesystem syncing work. For simple filesystems sync_inodes_sb(sb, 0)

 * just dirties buffers with inodes so we have to submit IO for these buffers

 * via __sync_blockdev(). This also speeds up the wait == 1 case since in that

 * case write_inode() functions do sync_dirty_buffer() and thus effectively

 * write one block at a time.

 */

static int __fsync_super(struct super_block *sb)

static int __fsync_super(struct super_block *sb, int wait)

{

	sync_inodes_sb(sb, 0);

	vfs_dq_sync(sb);

	sync_inodes_sb(sb, 1);

	sync_inodes_sb(sb, wait);

	lock_super(sb);

	if (sb->s_dirt && sb->s_op->write_super)

		sb->s_op->write_super(sb);

	unlock_super(sb);

	if (sb->s_op->sync_fs)

		sb->s_op->sync_fs(sb, 1);

	return sync_blockdev(sb->s_bdev);

		sb->s_op->sync_fs(sb, wait);

	return __sync_blockdev(sb->s_bdev, wait);

}



/*
@@ -310,7 +310,12 @@ static int __fsync_super(struct super_block *sb) 
 */

int fsync_super(struct super_block *sb)

{

	return __fsync_super(sb);

	int ret;



	ret = __fsync_super(sb, 0);

	if (ret < 0)

		return ret;

	return __fsync_super(sb, 1);

}

EXPORT_SYMBOL_GPL(fsync_super);
@@ -469,20 +474,18 @@ restart: 
}



/*

 * Call the ->sync_fs super_op against all filesystems which are r/w and

 * which implement it.

 * Sync all the data for all the filesystems (called by sys_sync() and

 * emergency sync)

 *

 * This operation is careful to avoid the livelock which could easily happen

 * if two or more filesystems are being continuously dirtied.  s_need_sync_fs

 * if two or more filesystems are being continuously dirtied.  s_need_sync

 * is used only here.  We set it against all filesystems and then clear it as

 * we sync them.  So redirtied filesystems are skipped.

 *

 * But if process A is currently running sync_filesystems and then process B

 * calls sync_filesystems as well, process B will set all the s_need_sync_fs

 * calls sync_filesystems as well, process B will set all the s_need_sync

 * flags again, which will cause process A to resync everything.  Fix that with

 * a local mutex.

 *

 * (Fabian) Avoid sync_fs with clean fs & wait mode 0

 */

void sync_filesystems(int wait)

{
@@ -492,25 +495,23 @@ void sync_filesystems(int wait) 
	mutex_lock(&mutex);		/* Could be down_interruptible */

	spin_lock(&sb_lock);

	list_for_each_entry(sb, &super_blocks, s_list) {

		if (!sb->s_op->sync_fs)

			continue;

		if (sb->s_flags & MS_RDONLY)

			continue;

		sb->s_need_sync_fs = 1;

		sb->s_need_sync = 1;

	}



restart:

	list_for_each_entry(sb, &super_blocks, s_list) {

		if (!sb->s_need_sync_fs)

		if (!sb->s_need_sync)

			continue;

		sb->s_need_sync_fs = 0;

		sb->s_need_sync = 0;

		if (sb->s_flags & MS_RDONLY)

			continue;	/* hm.  Was remounted r/o meanwhile */

		sb->s_count++;

		spin_unlock(&sb_lock);

		down_read(&sb->s_umount);

		if (sb->s_root)

			sb->s_op->sync_fs(sb, wait);

			__fsync_super(sb, wait);

		up_read(&sb->s_umount);

		/* restart only when sb is no longer on the list */

		spin_lock(&sb_lock);
@@ -521,33 +522,6 @@ restart: 
	mutex_unlock(&mutex);

}



#ifdef CONFIG_BLOCK

/*

 *  Sync all block devices underlying some superblock

 */

void sync_blockdevs(void)

{

	struct super_block *sb;



	spin_lock(&sb_lock);

restart:

	list_for_each_entry(sb, &super_blocks, s_list) {

		if (!sb->s_bdev)

			continue;

		sb->s_count++;

		spin_unlock(&sb_lock);

		down_read(&sb->s_umount);

		if (sb->s_root)

			sync_blockdev(sb->s_bdev);

		up_read(&sb->s_umount);

		spin_lock(&sb_lock);

		if (__put_super_and_need_restart(sb))

			goto restart;

	}

	spin_unlock(&sb_lock);

}

#endif



/**

 *	get_super - get the superblock of a device

 *	@bdev: device to get the superblock for

fs/sync.c

+10 −21
Original line number Diff line number Diff line
@@ -18,35 +18,24 @@ 
#define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \

			SYNC_FILE_RANGE_WAIT_AFTER)



/*

 * sync everything.  Start out by waking pdflush, because that writes back

 * all queues in parallel.

 */

static void do_sync(unsigned long wait)

SYSCALL_DEFINE0(sync)

{

	wakeup_pdflush(0);

	sync_inodes(0);		/* All mappings, inodes and their blockdevs */

	vfs_dq_sync(NULL);

	sync_inodes(wait);	/* Mappings, inodes and blockdevs, again. */

	sync_supers();		/* Write the superblocks */

	sync_filesystems(0);	/* Start syncing the filesystems */

	sync_filesystems(wait);	/* Waitingly sync the filesystems */

	sync_blockdevs();

	if (!wait)

		printk("Emergency Sync complete\n");

	sync_filesystems(0);

	sync_filesystems(1);

	if (unlikely(laptop_mode))

		laptop_sync_completion();

}



SYSCALL_DEFINE0(sync)

{

	do_sync(1);

	return 0;

}



static void do_sync_work(struct work_struct *work)

{

	do_sync(0);

	/*

	 * Sync twice to reduce the possibility we skipped some inodes / pages

	 * because they were temporarily locked

	 */

	sync_filesystems(0);

	sync_filesystems(0);

	printk("Emergency Sync complete\n");

	kfree(work);

}