xfs: fix filesystsem freeze race in xfs_trans_alloc

As pointed out by Jan xfs_trans_alloc can race with a concurrent filesystem
freeze when it sleeps during the memory allocation.  Fix this by moving the
wait_for_freeze call after the memory allocation.  This means moving the
freeze into the low-level _xfs_trans_alloc helper, which thus grows a new
argument.  Also fix up some comments in that area while at it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <david@fromorbit.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index b49b82363d20..63659ee316bd 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1566,15 +1566,9 @@ xfs_fs_writable(xfs_mount_t *mp)
 }
 
 /*
- * xfs_log_sbcount
- *
  * Called either periodically to keep the on disk superblock values
  * roughly up to date or from unmount to make sure the values are
  * correct on a clean unmount.
- *
- * Note this code can be called during the process of freezing, so
- * we may need to use the transaction allocator which does not not
- * block when the transaction subsystem is in its frozen state.
  */
 int
 xfs_log_sbcount(
@@ -1596,7 +1590,13 @@ xfs_log_sbcount(
         if (!xfs_sb_version_haslazysbcount(&mp->m_sb))
                 return 0;
 
-        tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP);
+        /*
+         * We can be called during the process of freezing, so make sure
+         * we go ahead even if the frozen for new transactions.  We will
+         * always use a sync transaction in the freeze path to make sure
+         * the transaction has completed by the time we return.
+         */
+        tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP, false);
         error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
                                         XFS_DEFAULT_LOG_COUNT);
         if (error) {