[PATCH 3.12 011/142] Btrfs: read lock extent buffer while walking backrefs

[Jiri Slaby]

From: Filipe Manana <fdmanana@xxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 6f7ff6d7832c6be13e8c95598884dbc40ad69fb7 upstream.

Before processing the extent buffer, acquire a read lock on it, so
that we're safe against concurrent updates on the extent buffer.

Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Chris Mason <clm@xxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 fs/btrfs/backref.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 715cfa42e182..53039de1495d 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -954,8 +954,11 @@ again:
 					ret = -EIO;
 					goto out;
 				}
+				btrfs_tree_read_lock(eb);
+				btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
 				ret = find_extent_in_eb(eb, bytenr,
 							*extent_item_pos, &eie);
+				btrfs_tree_read_unlock_blocking(eb);
 				free_extent_buffer(eb);
 				if (ret < 0)
 					goto out;
-- 
2.1.0

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