From: Sagi Grimberg <sagi@grimberg.me>
To: Chao Leng <lengchao@huawei.com>, Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <kbusch@kernel.org>,
linux-nvme@lists.infradead.org,
Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
Subject: Re: [PATCH 0/3 rfc] Fix nvme-tcp and nvme-rdma controller reset hangs
Date: Wed, 17 Mar 2021 11:43:59 -0700 [thread overview]
Message-ID: <6c085430-cc10-a2fd-56ee-a360109c940a@grimberg.me> (raw)
In-Reply-To: <2e391aae-58c7-b8f7-1a9e-d7ad5bb3f8f3@huawei.com>
>>>>> Will it work if nvme mpath used request NOWAIT flag for its
>>>>> submit_bio()
>>>>> call, and add the bio to the requeue_list if blk_queue_enter()
>>>>> fails? I
>>>>> think that looks like another way to resolve the deadlock, but we need
>>>>> the block layer to return a failed status to the original caller.
>>
>> Yes, I think BLK_MQ_REQ_NOWAIT makes total sense here. dm-mpath also
>> uses it for its request allocation for similar reasons.
>>
>>>>
>>>> But who would kick the requeue list? and that would make
>>>> near-tag-exhaust performance stink...
>>
>> The multipath code would have to kick the list. We could also try to
>> split into two flags, one that affects blk_queue_enter and one that
>> affects the tag allocation.
>>
>>> moving nvme_start_freeze from nvme_rdma_teardown_io_queues to
>>> nvme_rdma_configure_io_queues can fix it.
>>> It can also avoid I/O hang long time if reconnection failed.
>>
>> Can you explain how we'd still ensure that no new commands get queued
>> during teardown using that scheme?
> 1. tear down will cancel all inflight requests, and then multipath will
> clear the path.
> 2. and then we may freeze the controler.
> 3. nvme_ns_head_submit_bio can not find the reconnection controller as
> valid path, so it is safe.
In non-mpath (which unfortunately is a valid use-case), there is no
failover, and we cannot freeze the queue after we stopped (and/or
started) the queues because then fail_non_ready_command() constantly
return BLK_STS_RESOURCE (just causing a re-submission over and over
again) and the freeze will never complete (the commands are still
inflight from the queue->g_usage_counter perspective).
So I think we should still start queue freeze before we quiesce
the queues.
I still don't see how the mpath NOWAIT suggestion works either...
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next prev parent reply other threads:[~2021-03-17 18:44 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 22:27 [PATCH 0/3 rfc] Fix nvme-tcp and nvme-rdma controller reset hangs Sagi Grimberg
2021-03-15 22:27 ` [PATCH 1/3] nvme: introduce nvme_ctrl_is_mpath helper Sagi Grimberg
2021-03-15 22:27 ` [PATCH 2/3] nvme-tcp: fix possible hang when trying to set a live path during I/O Sagi Grimberg
2021-03-15 22:27 ` [PATCH 3/3] nvme-rdma: " Sagi Grimberg
2021-03-16 3:24 ` [PATCH 0/3 rfc] Fix nvme-tcp and nvme-rdma controller reset hangs Chao Leng
2021-03-16 5:04 ` Sagi Grimberg
2021-03-16 6:18 ` Chao Leng
2021-03-16 6:25 ` Sagi Grimberg
2021-03-16 20:07 ` Sagi Grimberg
2021-03-16 20:42 ` Keith Busch
2021-03-16 23:51 ` Sagi Grimberg
2021-03-17 2:55 ` Chao Leng
2021-03-17 6:59 ` Christoph Hellwig
2021-03-17 7:59 ` Chao Leng
2021-03-17 18:43 ` Sagi Grimberg [this message]
2021-03-18 1:51 ` Chao Leng
2021-03-18 4:45 ` Christoph Hellwig
2021-03-18 18:46 ` Sagi Grimberg
2021-03-18 19:16 ` Keith Busch
2021-03-18 19:31 ` Sagi Grimberg
2021-03-18 21:52 ` Keith Busch
2021-03-18 22:45 ` Sagi Grimberg
2021-03-19 14:05 ` Christoph Hellwig
2021-03-19 17:28 ` Christoph Hellwig
2021-03-19 19:07 ` Keith Busch
2021-03-19 19:34 ` Sagi Grimberg
2021-03-20 6:11 ` Christoph Hellwig
2021-03-21 6:49 ` Sagi Grimberg
2021-03-22 6:34 ` Christoph Hellwig
2021-03-17 8:16 ` Sagi Grimberg
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