btrfs: don't start transaction when joining with TRANS_JOIN_NOSTART

When joining a transaction with TRANS_JOIN_NOSTART, if we don't find a
running transaction we end up creating one. This goes against the purpose
of TRANS_JOIN_NOSTART which is to join a running transaction if its state
is at or below the state TRANS_STATE_COMMIT_START, otherwise return an
-ENOENT error and don't start a new transaction. So fix this to not create
a new transaction if there's no running transaction at or below that
state.

CC: stable@vger.kernel.org # 4.14+
Fixes: a6d155d2e363 ("Btrfs: fix deadlock between fiemap and transaction commits")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 815f61d..6a2a125 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -292,10 +292,11 @@ loop:
        spin_unlock(&fs_info->trans_lock);
 
        /*
-        * If we are ATTACH, we just want to catch the current transaction,
-        * and commit it. If there is no transaction, just return ENOENT.
+        * If we are ATTACH or TRANS_JOIN_NOSTART, we just want to catch the
+        * current transaction, and commit it. If there is no transaction, just
+        * return ENOENT.
         */
-       if (type == TRANS_ATTACH)
+       if (type == TRANS_ATTACH || type == TRANS_JOIN_NOSTART)
                return -ENOENT;
 
        /*