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 <[email protected]> Signed-off-by: Damien Le Moal <[email protected]> --- 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
