From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagi@grimberg.me>, Jens Axboe <axboe@kernel.dk>,
Chao Leng <lengchao@huawei.com>,
linux-block@vger.kernel.org, linux-nvme@lists.infradead.org
Subject: Re: [PATCH 2/2] nvme-multipath: don't block on blk_queue_enter of the underlying device
Date: Tue, 23 Mar 2021 00:31:01 +0900 [thread overview]
Message-ID: <20210322153101.GB17311@redsun51.ssa.fujisawa.hgst.com> (raw)
In-Reply-To: <20210322073726.788347-3-hch@lst.de>
On Mon, Mar 22, 2021 at 08:37:26AM +0100, Christoph Hellwig wrote:
> When we reset/teardown a controller, we must freeze and quiesce the
> namespaces request queues to make sure that we safely stop inflight I/O
> submissions. Freeze is mandatory because if our hctx map changed between
> reconnects, blk_mq_update_nr_hw_queues will immediately attempt to freeze
> the queue, and if it still has pending submissions (that are still
> quiesced) it will hang.
>
> However, by freezing the namespaces request queues, and only unfreezing
> them when we successfully reconnect, inflight submissions that are
> running concurrently can now block grabbing the nshead srcu until either
> we successfully reconnect or ctrl_loss_tmo expired (or the user
> explicitly disconnected).
>
> This caused a deadlock when a different controller (different path on the
> same subsystem) became live (i.e. optimized/non-optimized). This is
> because nvme_mpath_set_live needs to synchronize the nshead srcu before
> requeueing I/O in order to make sure that current_path is visible to
> future (re-)submisions. However the srcu lock is taken by a blocked
> submission on a frozen request queue, and we have a deadlock.
>
> In order to fix this use the blk_mq_submit_bio_direct API to submit the
> bio to the low-level driver, which does not block on the queue free
> but instead allows nvme-multipath to pick another path or queue up the
> bio.
Looks good.
Reviewed-by: Keith Busch <kbusch@kernel.org>
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next prev parent reply other threads:[~2021-03-22 15:31 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 7:37 fix nvme-tcp and nvme-rdma controller reset hangs when using multipath Christoph Hellwig
2021-03-22 7:37 ` [PATCH 1/2] blk-mq: add a blk_mq_submit_bio_direct API Christoph Hellwig
2021-03-22 11:23 ` Hannes Reinecke
2021-03-22 15:30 ` Keith Busch
2021-03-22 7:37 ` [PATCH 2/2] nvme-multipath: don't block on blk_queue_enter of the underlying device Christoph Hellwig
2021-03-22 11:22 ` Hannes Reinecke
2021-03-22 15:31 ` Keith Busch [this message]
2021-03-23 2:57 ` Sagi Grimberg
2021-03-23 3:23 ` Sagi Grimberg
2021-03-23 7:04 ` Chao Leng
2021-03-23 7:36 ` Sagi Grimberg
2021-03-23 8:13 ` Chao Leng
2021-03-23 16:17 ` Christoph Hellwig
2021-03-23 16:15 ` Christoph Hellwig
2021-03-23 18:13 ` Sagi Grimberg
2021-03-23 18:22 ` Christoph Hellwig
2021-03-23 19:00 ` Sagi Grimberg
2021-03-23 19:01 ` Christoph Hellwig
2021-03-23 19:10 ` Sagi Grimberg
2021-03-23 7:28 ` Hannes Reinecke
2021-03-23 7:31 ` Sagi Grimberg
2021-03-23 8:36 ` Hannes Reinecke
2021-03-23 14:53 ` Keith Busch
2021-03-23 16:19 ` Christoph Hellwig
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