[PATCH 1/6] xfs: check if_bytes under the ilock in xfs_reflink_end_cow_extent

From: Christoph Hellwig <hch@lst.de>
To: Chandan Babu R <chandan.babu@oracle.com>,
	"Darrick J. Wong" <djwong@kernel.org>
Cc: linux-xfs@vger.kernel.org
Subject: [PATCH 1/6] xfs: check if_bytes under the ilock in xfs_reflink_end_cow_extent
Date: Thu, 28 Mar 2024 08:02:51 +0100	[thread overview]
Message-ID: <20240328070256.2918605-2-hch@lst.de> (raw)
In-Reply-To: <20240328070256.2918605-1-hch@lst.de>

Accessing if_bytes without the ilock is racy.  Move the check a little
further down into the ilock critical section.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_reflink.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 7da0e8f961d351..df632790a0a51c 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -731,12 +731,6 @@ xfs_reflink_end_cow_extent(
 	int			nmaps;
 	int			error;
 
-	/* No COW extents?  That's easy! */
-	if (ifp->if_bytes == 0) {
-		*offset_fsb = end_fsb;
-		return 0;
-	}
-
 	resblks = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
 	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0,
 			XFS_TRANS_RESERVE, &tp);
@@ -751,6 +745,12 @@ xfs_reflink_end_cow_extent(
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 	xfs_trans_ijoin(tp, ip, 0);
 
+	/* No COW extents?  That's easy! */
+	if (ifp->if_bytes == 0) {
+		*offset_fsb = end_fsb;
+		goto out_cancel;
+	}
+
 	error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
 			XFS_IEXT_REFLINK_END_COW_CNT);
 	if (error == -EFBIG)
-- 
2.39.2

