A BIO based request queue does not have a tag_set, which prevent testing
for the flag BLK_MQ_F_NO_SCHED indicating that the queue does not
require an elevator. This leads to an incorrect initialization of a
default elevator in some cases such as BIO based null_blk
(queue_mode == BIO) with zoned mode enabled as the default elevator in
this case is mq-deadline instead of "none".
Fix this by testing for a NULL queue mq_ops field which indicates that
the queue is BIO based and should not have an elevator.
Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
---
Changes from V1:
* Test if q->mq_ops is NULL to identify BIO based queues
block/elevator.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/block/elevator.c b/block/elevator.c
index 5437059c9261..076ba7308e65 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -616,7 +616,8 @@ int elevator_switch_mq(struct request_queue *q,
static inline bool elv_support_iosched(struct request_queue *q)
{
- if (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED))
+ if (!q->mq_ops ||
+ (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED)))
return false;
return true;
}
--
2.21.0
