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Commit 51561ffe authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
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Btrfs: lock the transition from dirty to writeback for an eb 



There is a small window where an eb can have no IO bits set on it, which
could potentially result in extent_buffer_under_io() returning false when we
want it to return true, which could result in not fun things happening.  So
in order to protect this case we need to hold the refs_lock when we make
this transition to make sure we get reliable results out of
extent_buffer_udner_io().  Thanks,

Signed-off-by: default avatarJosef Bacik <jbacik@fusionio.com>
parent 594831c4

fs/btrfs/extent_io.c

+9 −0
Original line number Diff line number Diff line
@@ -3077,8 +3077,15 @@ static int lock_extent_buffer_for_io(struct extent_buffer *eb, 
		}

	}



	/*

	 * We need to do this to prevent races in people who check if the eb is

	 * under IO since we can end up having no IO bits set for a short period

	 * of time.

	 */

	spin_lock(&eb->refs_lock);

	if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {

		set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);

		spin_unlock(&eb->refs_lock);

		btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);

		spin_lock(&fs_info->delalloc_lock);

		if (fs_info->dirty_metadata_bytes >= eb->len)
@@ -3087,6 +3094,8 @@ static int lock_extent_buffer_for_io(struct extent_buffer *eb, 
			WARN_ON(1);

		spin_unlock(&fs_info->delalloc_lock);

		ret = 1;

	} else {

		spin_unlock(&eb->refs_lock);

	}



	btrfs_tree_unlock(eb);