[PATCH] block: revert to using min_not_zero() when stacking chunk_sectors

[Mike Snitzer <snitzer@redhat.com>]

chunk_sectors must reflect the most limited of all devices in the IO
stack.

Otherwise malformed IO may result. E.g.: prior to this fix,
->chunk_sectors = lcm_not_zero(8, 128) would result in
blk_max_size_offset() splitting IO at 128 sectors rather than the
required more restrictive 8 sectors.

Fixes: 22ada802ede8 ("block: use lcm_not_zero() when stacking chunk_sectors")
Cc: stable@vger.kernel.org
Reported-by: John Dorminy <jdorminy@redhat.com>
Reported-by: Bruce Johnston <bjohnsto@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 block/blk-settings.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 9741d1d83e98..1d9decd4646e 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -547,7 +547,10 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 
 	t->io_min = max(t->io_min, b->io_min);
 	t->io_opt = lcm_not_zero(t->io_opt, b->io_opt);
-	t->chunk_sectors = lcm_not_zero(t->chunk_sectors, b->chunk_sectors);
+
+	if (b->chunk_sectors)
+		t->chunk_sectors = min_not_zero(t->chunk_sectors,
+						b->chunk_sectors);
 
 	/* Physical block size a multiple of the logical block size? */
 	if (t->physical_block_size & (t->logical_block_size - 1)) {
-- 
2.15.0