Btrfs: Add a skip_locking parameter to struct path, and make various funcs honor it

Allocations may need to read in block groups from the extent allocation tree,
which will require a tree search and take locks on the extent allocation
tree.  But, those locks might already be held in other places, leading
to deadlocks.

Since the alloc_mutex serializes everything right now, it is safe to
skip the btree locking while caching block groups.  A better fix will be
to either create a recursive lock or find a way to back off existing
locks while caching block groups.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 9ea12d4..e9bbb53 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -335,6 +335,7 @@ struct btrfs_path {
 	int reada;
 	/* keep some upper locks as we walk down */
 	int keep_locks;
+	int skip_locking;
 	int lowest_level;
 };