Btrfs: Use btrfs_join_transaction to avoid deadlocks during snapshot creation

Snapshot creation happens at a specific time during transaction commit.  We
need to make sure the code called by snapshot creation doesn't wait
for the running transaction to commit.

This changes btrfs_delete_inode and finish_pending_snaps to use
btrfs_join_transaction instead of btrfs_start_transaction to avoid deadlocks.

It would be better if btrfs_delete_inode didn't use the join, but the
call path that triggers it is:

btrfs_commit_transaction->create_pending_snapshots->
create_pending_snapshot->btrfs_lookup_dentry->
fixup_tree_root_location->btrfs_read_fs_root->
btrfs_read_fs_root_no_name->btrfs_orphan_cleanup->iput

This will be fixed in a later patch by moving the orphan cleanup to the
cleaner thread.

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

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 56ab1f5ea11b..8a08f9443340 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -800,7 +800,7 @@ static noinline int finish_pending_snapshot(struct btrfs_fs_info *fs_info,
 
         parent_inode = pending->dentry->d_parent->d_inode;
         parent_root = BTRFS_I(parent_inode)->root;
-        trans = btrfs_start_transaction(parent_root, 1);
+        trans = btrfs_join_transaction(parent_root, 1);
 
         /*
          * insert the directory item