From: Keith Busch <kbusch@kernel.org>
To: Dongli Zhang <dongli.zhang@oracle.com>
Cc: linux-block@vger.kernel.org, Sagi Grimberg <sagi@grimberg.me>,
linux-nvme@lists.infradead.org
Subject: Re: nvme double __blk_mq_complete_request() bugs
Date: Mon, 25 May 2020 10:45:16 -0600 [thread overview]
Message-ID: <20200525164516.GC73686@C02WT3WMHTD6> (raw)
In-Reply-To: <49f32df9-81a9-4c15-9950-aceff8fb291e@oracle.com>
On Sun, May 24, 2020 at 07:33:02AM -0700, Dongli Zhang wrote:
> >> After code analysis, I think this is for nvme-pci as well.
> >>
> >> nvme_process_cq()
> >> -> nvme_handle_cqe()
> >> -> nvme_end_request()
> >> -> blk_mq_complete_request()
> >> nvme_reset_work()
> >> -> nvme_dev_disable()
> >> -> nvme_reap_pending_cqes()
> >> -> nvme_process_cq()
> >> -> nvme_handle_cqe()
> >> -> nvme_end_request()
> >> -> blk_mq_complete_request()
> >> -> __blk_mq_complete_request()
> >> -> __blk_mq_complete_request()
> >
> > nvme_dev_disable will first disable the queues before reaping the pending cqes so
> > it shouldn't have this issue.
> >
>
> Would you mind help explain how nvme_dev_disable() would avoid this issue?
>
> nvme_dev_disable() would:
>
> 1. freeze all the queues so that new request would not enter and submit
> 2. NOT wait for freezing during live reset so that q->q_usage_counter is not
> guaranteed to be zero.
> 3. quiesce all the queues so that new request would not dispatch
> 4. delete the queue and free irq
>
> However, I do not find a mechanism to prevent if a nvme_end_request() is already
> in progress.
>
> E.g., suppose __blk_mq_complete_request() is already triggered on cpu 3 and
> waiting for its first line "WRITE_ONCE(rq->state, MQ_RQ_COMPLETE)" to be
> executed ... while another cpu is doing live reset. I do not see how to prevent
> such race.
The queues and their interrupts are torn and synchronized down before the reset
reclaims uncompleted requests. There's no other context that can be running
completions at that point.
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next prev parent reply other threads:[~2020-05-25 16:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-18 4:30 nvme double __blk_mq_complete_request() bugs Dongli Zhang
2020-05-18 7:51 ` Sagi Grimberg
2020-05-24 14:33 ` Dongli Zhang
2020-05-25 16:45 ` Keith Busch [this message]
2020-05-27 1:04 ` Dongli Zhang
2020-05-27 3:36 ` Keith Busch
2020-05-27 4:14 ` Dongli Zhang
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