[PATCH v2 2/2] xfs: restore nofs context unconditionally in xfs_trans_roll

[Yun Zhou]

When __xfs_trans_commit() fails in xfs_trans_roll(), the NOFS context
is cleared but only restored in the success path.  This leaves the
error path without nofs protection, causing a circular lock dependency
between xfs_nondir_ilock_class and fs_reclaim:

       CPU0                    CPU1
       ----                    ----
  lock(&xfs_nondir_ilock_class);
                               lock(fs_reclaim);
                               lock(&xfs_nondir_ilock_class);
  lock(fs_reclaim);

Fix this by transferring the nofs context from the old transaction to
the new one in xfs_trans_dup() via memalloc_flags_move(), so it remains
active throughout the entire roll sequence regardless of commit success
or failure.

Reported-by: syzbot+59178abfeb0ea3f0ab20@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=59178abfeb0ea3f0ab20
Fixes: a1ca658d649a ("xfs: fix incorrect context handling in xfs_trans_roll")
Suggested-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Signed-off-by: Yun Zhou <yun.zhou@xxxxxxxxxxxxx>
---
 fs/xfs/xfs_trans.c | 9 +++------
 fs/xfs/xfs_trans.h | 2 +-
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 7bfbd9f6f0df..89818c67b64f 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -127,6 +127,9 @@ xfs_trans_dup(
 	/* move deferred ops over to the new tp */
 	xfs_defer_move(ntp, tp);
 
+	/* move the nofs context to the new transaction */
+	ntp->t_pflags = memalloc_flags_move(&tp->t_pflags);
+
 	xfs_trans_dup_dqinfo(tp, ntp);
 	return ntp;
 }
@@ -1041,12 +1044,6 @@ xfs_trans_roll(
 	 * locked be logged in the prior and the next transactions.
 	 */
 	tp = *tpp;
-	/*
-	 * __xfs_trans_commit cleared the NOFS flag by calling into
-	 * xfs_trans_free.  Set it again here before doing memory
-	 * allocations.
-	 */
-	xfs_trans_set_context(tp);
 	error = xfs_log_regrant(tp->t_mountp, tp->t_ticket);
 	if (error)
 		return error;
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index eb83c5dac032..fd792584275a 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -152,7 +152,7 @@ typedef struct xfs_trans {
 	struct list_head	t_items;	/* log item descriptors */
 	struct list_head	t_busy;		/* list of busy extents */
 	struct list_head	t_dfops;	/* deferred operations */
-	unsigned long		t_pflags;	/* saved process flags state */
+	unsigned int		t_pflags;	/* saved process flags state */
 } xfs_trans_t;
 
 /*
-- 
2.43.0