btrfs: Document a mutex lock/unlock sequence
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a160f11..fba1348 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -756,6 +756,10 @@
btrfs_release_path(path);
+ /*
+ * Mutex was contended, block until it's released and try
+ * again
+ */
mutex_lock(&head->mutex);
mutex_unlock(&head->mutex);
btrfs_put_delayed_ref(&head->node);
@@ -2297,6 +2301,10 @@
atomic_inc(&ref->refs);
spin_unlock(&delayed_refs->lock);
+ /*
+ * Mutex was contended, block until it's
+ * released and try again
+ */
mutex_lock(&head->mutex);
mutex_unlock(&head->mutex);
@@ -2363,6 +2371,10 @@
btrfs_release_path(path);
+ /*
+ * Mutex was contended, block until it's released and let
+ * caller try again
+ */
mutex_lock(&head->mutex);
mutex_unlock(&head->mutex);
btrfs_put_delayed_ref(&head->node);
