From: Sagi Grimberg <sagi@grimberg.me>
To: Christoph Hellwig <hch@lst.de>, Chao Leng <lengchao@huawei.com>
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 01:16:26 -0700 [thread overview]
Message-ID: <a5a0c334-6fdc-07c9-f8dc-5d3eb13ec0b2@grimberg.me> (raw)
In-Reply-To: <20210317065910.GC14498@lst.de>
>>>> 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.
BTW, the specific hang reported is not blocking on tag allocation, but
rather than on blk_queue_enter blocking on a frozen queue.
> dm-mpath also uses it for its request allocation for similar reasons.
That is the rq based dm, and I think it is because dm_mq_queue_rq is
non-blocking. Care to explain what is similar to nvme-mpath?
I don't see how bio based dm cares about any of this...
>>> 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.
When? Not following your thoughts...
You are suggesting that we call submit_bio that will fail, put it on the
requeue_list and then what? blindly kick the requeue list? try to see if
there is an alternate path and then kick the list? for every bio that
comes in?
> We could also try to
> split into two flags, one that affects blk_queue_enter and one that
> affects the tag allocation.
If this is something that can work reliably then its better off, plus we
can probably kill the srcu as well. But I don't see how this would
work unfortunately.
>> 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?
quiescing the queue would prevent new submissions from coming down to
the driver, but I don't see how this move can help here...
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prev parent reply other threads:[~2021-03-17 8:16 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
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 [this message]
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