btrfs: fix deadlock in delayed_ref_async_start

"Btrfs: track transid for delayed ref flushing" was deadlocking on
btrfs_attach_transaction because its not safe to call from the async
delayed ref start code.  This commit brings back btrfs_join_transaction
instead and checks for a blocked commit.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index ecfa520..82b912a 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2851,16 +2851,13 @@ static void delayed_ref_async_start(struct btrfs_work *work)
 
        async = container_of(work, struct async_delayed_refs, work);
 
-       trans = btrfs_attach_transaction(async->root);
-       if (IS_ERR(trans)) {
-               if (PTR_ERR(trans) != -ENOENT)
-                       async->error = PTR_ERR(trans);
+       /* if the commit is already started, we don't need to wait here */
+       if (btrfs_transaction_blocked(async->root->fs_info))
                goto done;
-       }
 
-       /* Don't bother flushing if we got into a different transaction */
-       if (trans->transid != async->transid) {
-               btrfs_end_transaction(trans, async->root);
+       trans = btrfs_join_transaction(async->root);
+       if (IS_ERR(trans)) {
+               async->error = PTR_ERR(trans);
                goto done;
        }
 
@@ -2869,10 +2866,15 @@ static void delayed_ref_async_start(struct btrfs_work *work)
         * wait on delayed refs
         */
        trans->sync = true;
+
+       /* Don't bother flushing if we got into a different transaction */
+       if (trans->transid > async->transid)
+               goto end;
+
        ret = btrfs_run_delayed_refs(trans, async->root, async->count);
        if (ret)
                async->error = ret;
-
+end:
        ret = btrfs_end_transaction(trans, async->root);
        if (ret && !async->error)
                async->error = ret;