Messages in this thread | | | Date | Fri, 18 Aug 2023 01:17:38 +0800 | Subject | Re: [PATCH v2] blk-mq: release scheduler resource when request complete | From | Chengming Zhou <> |
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On 2023/8/17 23:29, Chengming Zhou wrote: > On 2023/8/17 22:50, Bart Van Assche wrote: >> On 8/17/23 07:41, kernel test robot wrote: >>> [ 222.622837][ T2216] statistics for priority 1: i 276 m 0 d 276 c 278 >>> [ 222.629307][ T2216] WARNING: CPU: 0 PID: 2216 at block/mq-deadline.c:680 dd_exit_sched (block/mq-deadline.c:680 (discriminator 3)) >> >> The above information shows that dd_inserted_request() has been called >> 276 times and also that dd_finish_request() has been called 278 times. > > Thanks much for your help. > > This patch indeed introduced a regression, postflush requests will be completed > twice, so here dd_finish_request() is more than dd_inserted_request(). > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index a8c63bef8ff1..7cd47ffc04ce 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -686,8 +686,10 @@ static void blk_mq_finish_request(struct request *rq) > { > struct request_queue *q = rq->q; > > - if (rq->rq_flags & RQF_USE_SCHED) > + if (rq->rq_flags & RQF_USE_SCHED) { > q->elevator->type->ops.finish_request(rq); > + rq->rq_flags &= ~RQF_USE_SCHED; > + } > } >
I just tried to run LKP and xfstests, firstly failed to run LKP on my server which seems to miss some dependencies. Then I ran xfstests successfully.
But xfstests generic/704 always pass and no WARN in dmesg. (I don't know why, maybe my server settings are some different from the test robot.)
So I try to reproduce it manually. Steps:
``` echo mq-deadline > /sys/block/sdb/queue/scheduler
mkfs.ext4 /dev/sdb mount /dev/sdb /fs/sdb cd /fs/sdb stress-ng --symlink 4 --timeout 60
echo none > /sys/block/sdb/queue/scheduler ```
This way the WARNING in mq-deadline can be reproduced easily.
Then retest with the diff, mq-deadline WARNING still happened... So there are still other requests which have RQF_USE_SCHED flag completed without being inserted into elevator.
Will use some tracing and look again.
Thanks.
> > Clear RQF_USE_SCHED flag here should fix this problem, which should be ok > since finish_request() is the last callback, this flag isn't needed anymore. > > Jens, should I send this diff as another patch or resend updated v3? > > Thanks. > >> Calling dd_finish_request() more than once per request breaks the code >> for priority handling since that code checks how many requests are >> pending per priority level by subtracting the number of completion calls >> from the number of insertion calls (see also dd_queued()). I think the >> above output indicates that this patch introduced a regression. >> >> Bart. >>
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