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>

1 files changed, 11 insertions, 9 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index ecfa52002363..82b912a293ab 100644
--- 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;