2017-03-30 05:20:55

by Minchan Kim

[permalink] [raw]
Subject: [PATCH] block: do not put mq context in blk_mq_alloc_request_hctx

In blk_mq_alloc_request_hctx, blk_mq_sched_get_request doesn't
get sw context so we don't need to put the context with
blk_mq_put_ctx. Unless, we will see preempt counter underflow.

Cc: Sagi Grimberg <[email protected]>
Cc: Omar Sandoval <[email protected]>
Cc: Jens Axboe <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
---

Maybe, it would be fixed by someone but I have noticed preempt counter
undeflow problem a few weeks ago and still see the problem with
linux-next.

block/blk-mq.c | 1 -
1 file changed, 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a4546f060e80..a6f3998dc4ee 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -321,7 +321,6 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q, int rw,

rq = blk_mq_sched_get_request(q, NULL, rw, &alloc_data);

- blk_mq_put_ctx(alloc_data.ctx);
blk_queue_exit(q);

if (!rq)
--
2.7.4


2017-03-30 14:23:19

by Jens Axboe

[permalink] [raw]
Subject: Re: [PATCH] block: do not put mq context in blk_mq_alloc_request_hctx

On 03/29/2017 11:20 PM, Minchan Kim wrote:
> In blk_mq_alloc_request_hctx, blk_mq_sched_get_request doesn't
> get sw context so we don't need to put the context with
> blk_mq_put_ctx. Unless, we will see preempt counter underflow.

Good catch, that's definitely a bug. I have applied your patch
for 4.11.

--
Jens Axboe