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>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 0905653..544fc3f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -88,6 +88,12 @@
return -ENOMEM;
path->reada = 2;
+ /*
+ * we get into deadlocks with paths held by callers of this function.
+ * since the alloc_mutex is protecting things right now, just
+ * skip the locking here
+ */
+ path->skip_locking = 1;
first_free = block_group->key.objectid;
key.objectid = block_group->key.objectid;
key.offset = 0;
