[PATCH 5.10.y] xfs: cap the block count of xfs_iomap_write_direct() at one extent

[Sasha Levin <sashal@kernel.org>]

From: Daejun Park <daejun7.park@samsung.com>

[ Upstream commit 66d1ce09ebd72709f8d739630c39f440445173fd ]

xfs_iomap_write_direct() reserves blocks for the whole count in an
unsigned int. For a pNFS layout the client chooses that count, and an
RW LAYOUTGET for 16 TiB wraps the reservation and shuts XFS down.

xfs_bmapi_write() maps at most XFS_MAX_BMBT_EXTLEN blocks here, so cap
the count at that. nfsd asks again for the rest. The other callers get
the same mapping as before.

Suggested-by: Darrick J. Wong <djwong@kernel.org>
Suggested-by: Christoph Hellwig <hch@lst.de>
Suggested-by: Pankaj Raghav <p.raghav@samsung.com>
Fixes: 527851124d10 ("xfs: implement pNFS export operations")
Cc: stable@vger.kernel.org
Signed-off-by: Daejun Park <daejun7.park@samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
[ sashal: Replaced XFS_MAX_BMBT_EXTLEN with the equivalent MAXEXTLEN constant in the expression and comment. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/xfs/xfs_iomap.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index bd5a25f4952d0..2f7cce023c0e8 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -203,6 +203,14 @@ xfs_iomap_write_direct(
 
 	ASSERT(count_fsb > 0);
 
+	/*
+	 * xfs_bmapi_write() maps at most MAXEXTLEN blocks in one
+	 * mapping, so don't reserve blocks for more. A pNFS layout range
+	 * comes from a client, and its block count may not even fit the
+	 * 32-bit reservation. The caller maps the rest with a later call.
+	 */
+	count_fsb = min_t(xfs_filblks_t, count_fsb, MAXEXTLEN);
+
 	resaligned = xfs_aligned_fsb_count(offset_fsb, count_fsb,
 					   xfs_get_extsz_hint(ip));
 	if (unlikely(XFS_IS_REALTIME_INODE(ip))) {
-- 
2.53.0