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, 10 insertions, 17 deletions

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index c83f63b33aa..2837220ea5c 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -566,31 +566,24 @@ xfs_trans_init(
 
 /*
  * This routine is called to allocate a transaction structure.
+ *
  * The type parameter indicates the type of the transaction.  These
  * are enumerated in xfs_trans.h.
- *
- * Dynamically allocate the transaction structure from the transaction
- * zone, initialize it, and return it to the caller.
  */
-xfs_trans_t *
-xfs_trans_alloc(
-        xfs_mount_t     *mp,
-        uint            type)
-{
-        xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
-        return _xfs_trans_alloc(mp, type, KM_SLEEP);
-}
-
-xfs_trans_t *
+struct xfs_trans *
 _xfs_trans_alloc(
-        xfs_mount_t     *mp,
-        uint            type,
-        uint            memflags)
+        struct xfs_mount        *mp,
+        uint                    type,
+        uint                    memflags,
+        bool                    wait_for_freeze)
 {
-        xfs_trans_t     *tp;
+        struct xfs_trans        *tp;
 
         atomic_inc(&mp->m_active_trans);
 
+        if (wait_for_freeze)
+                xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
+
         tp = kmem_zone_zalloc(xfs_trans_zone, memflags);
         tp->t_magic = XFS_TRANS_MAGIC;
         tp->t_type = type;