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Commit 38f21977 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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fs: sync_sb_inodes fix 



Fix data integrity semantics required by sys_sync, by iterating over all
inodes and waiting for any writeback pages after the initial writeout.
Comments explain the exact problem.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4f5a99d6

fs/fs-writeback.c

+53 −7
Original line number Diff line number Diff line
@@ -440,6 +440,7 @@ void generic_sync_sb_inodes(struct super_block *sb, 
				struct writeback_control *wbc)

{

	const unsigned long start = jiffies;	/* livelock avoidance */

	int sync = wbc->sync_mode == WB_SYNC_ALL;



	spin_lock(&inode_lock);

	if (!wbc->for_kupdate || list_empty(&sb->s_io))
@@ -516,7 +517,49 @@ void generic_sync_sb_inodes(struct super_block *sb, 
		if (!list_empty(&sb->s_more_io))

			wbc->more_io = 1;

	}



	if (sync) {

		struct inode *inode, *old_inode = NULL;



		/*

		 * Data integrity sync. Must wait for all pages under writeback,

		 * because there may have been pages dirtied before our sync

		 * call, but which had writeout started before we write it out.

		 * In which case, the inode may not be on the dirty list, but

		 * we still have to wait for that writeout.

		 */

		list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {

			struct address_space *mapping;



			if (inode->i_state & (I_FREEING|I_WILL_FREE))

				continue;

			mapping = inode->i_mapping;

			if (mapping->nrpages == 0)

				continue;

			__iget(inode);

			spin_unlock(&inode_lock);

			/*

			 * We hold a reference to 'inode' so it couldn't have

			 * been removed from s_inodes list while we dropped the

			 * inode_lock.  We cannot iput the inode now as we can

			 * be holding the last reference and we cannot iput it

			 * under inode_lock. So we keep the reference and iput

			 * it later.

			 */

			iput(old_inode);

			old_inode = inode;



			filemap_fdatawait(mapping);



			cond_resched();



			spin_lock(&inode_lock);

		}

		spin_unlock(&inode_lock);

		iput(old_inode);

	} else

		spin_unlock(&inode_lock);



	return;		/* Leave any unwritten inodes on s_io */

}

EXPORT_SYMBOL_GPL(generic_sync_sb_inodes);
@@ -596,13 +639,16 @@ void sync_inodes_sb(struct super_block *sb, int wait) 
		.range_start	= 0,

		.range_end	= LLONG_MAX,

	};



	if (!wait) {

		unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);

		unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);



		wbc.nr_to_write = nr_dirty + nr_unstable +

			(inodes_stat.nr_inodes - inodes_stat.nr_unused) +

			nr_dirty + nr_unstable;

	wbc.nr_to_write += wbc.nr_to_write / 2;		/* Bit more for luck */

			(inodes_stat.nr_inodes - inodes_stat.nr_unused);

	} else

		wbc.nr_to_write = LONG_MAX; /* doesn't actually matter */



	sync_sb_inodes(sb, &wbc);

}