[PATCH] dm: retain stacked max_sectors when setting queue_limits

[Mike Snitzer <snitzer@kernel.org>]

Otherwise, blk_validate_limits() will throw-away the max_sectors that
was stacked from underlying device(s). In doing so it can set a
max_sectors limit that violates underlying device limits.

This caused dm-multipath IO failures like the following because the
underlying devices' max_sectors were stacked up to be 1024, yet
blk_validate_limits() defaulted max_sectors to BLK_DEF_MAX_SECTORS_CAP
(2560):

[ 1214.673233] blk_insert_cloned_request: over max size limit. (2048 > 1024)
[ 1214.673267] device-mapper: multipath: 254:3: Failing path 8:32.
[ 1214.675196] blk_insert_cloned_request: over max size limit. (2048 > 1024)
[ 1214.675224] device-mapper: multipath: 254:3: Failing path 8:16.
[ 1214.675309] blk_insert_cloned_request: over max size limit. (2048 > 1024)
[ 1214.675338] device-mapper: multipath: 254:3: Failing path 8:48.
[ 1214.675413] blk_insert_cloned_request: over max size limit. (2048 > 1024)
[ 1214.675441] device-mapper: multipath: 254:3: Failing path 8:64.

The initial bug report included:

[   13.822701] blk_insert_cloned_request: over max size limit. (248 > 128)
[   13.829351] device-mapper: multipath: 253:3: Failing path 8:32.
[   13.835307] blk_insert_cloned_request: over max size limit. (248 > 128)
[   13.841928] device-mapper: multipath: 253:3: Failing path 65:16.
[   13.844532] blk_insert_cloned_request: over max size limit. (248 > 128)
[   13.854363] blk_insert_cloned_request: over max size limit. (248 > 128)
[   13.854580] device-mapper: multipath: 253:4: Failing path 8:48.
[   13.861166] device-mapper: multipath: 253:3: Failing path 8:192.

Reported-by: Marco Patalano <mpatalan@redhat.com>
Reported-by: Ewan Milne <emilne@redhat.com>
Fixes: 1c0e720228ad ("dm: use queue_limits_set")
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
 drivers/md/dm-table.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 88114719fe18..6463b4afeaa4 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1961,6 +1961,7 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 			      struct queue_limits *limits)
 {
 	bool wc = false, fua = false;
+	unsigned int max_hw_sectors;
 	int r;
 
 	if (dm_table_supports_nowait(t))
@@ -1981,9 +1982,16 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 	if (!dm_table_supports_secure_erase(t))
 		limits->max_secure_erase_sectors = 0;
 
+	/* Don't allow queue_limits_set() to throw-away stacked max_sectors */
+	max_hw_sectors = limits->max_hw_sectors;
+	limits->max_hw_sectors = limits->max_sectors;
 	r = queue_limits_set(q, limits);
 	if (r)
 		return r;
+	/* Restore stacked max_hw_sectors */
+	mutex_lock(&q->limits_lock);
+	limits->max_hw_sectors = max_hw_sectors;
+	mutex_unlock(&q->limits_lock);
 
 	if (dm_table_supports_flush(t, (1UL << QUEUE_FLAG_WC))) {
 		wc = true;
-- 
2.43.0