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

------------------

From: Josef Bacik <jba...@fusionio.com>

commit fec386ac1428f9c0e672df952cbca5cebd4e4e2f upstream.

We aren't setting path->locks[level] when we resume a snapshot deletion which
means we won't unlock the buffer when we free the path.  This causes deadlocks
if we happen to re-allocate the block before we've evicted the extent buffer
from cache.  Thanks,

Reported-by: Alex Lyakas <alex.bt...@zadarastorage.com>
Signed-off-by: Josef Bacik <jba...@fusionio.com>
Signed-off-by: Kamal Mostafa <ka...@canonical.com>
---
 fs/btrfs/extent-tree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d170412..17cfffd 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7023,6 +7023,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
                while (1) {
                        btrfs_tree_lock(path->nodes[level]);
                        btrfs_set_lock_blocking(path->nodes[level]);
+                       path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
 
                        ret = btrfs_lookup_extent_info(trans, root,
                                                path->nodes[level]->start,
@@ -7039,6 +7040,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
                                break;
 
                        btrfs_tree_unlock(path->nodes[level]);
+                       path->locks[level] = 0;
                        WARN_ON(wc->refs[level] != 1);
                        level--;
                }
-- 
1.8.1.2

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