xfs: allow empty transactions while frozen

In commit e89c041338ed6ef ("xfs: implement the GETFSMAP ioctl") we
created the ability to obtain empty transactions.  These transactions
have no log or block reservations and therefore can't modify anything.
Since they're also NO_WRITECOUNT they can run while the fs is frozen,
so we don't need to WARN_ON about that usage.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index e040af120b69..524f543c5b82 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -258,7 +258,12 @@ xfs_trans_alloc(
         if (!(flags & XFS_TRANS_NO_WRITECOUNT))
                 sb_start_intwrite(mp->m_super);
 
-        WARN_ON(mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE);
+        /*
+         * Zero-reservation ("empty") transactions can't modify anything, so
+         * they're allowed to run while we're frozen.
+         */
+        WARN_ON(resp->tr_logres > 0 &&
+                mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE);
         atomic_inc(&mp->m_active_trans);
 
         tp = kmem_zone_zalloc(xfs_trans_zone,