From: Ming Lei <ming.lei@redhat.com>
To: Keith Busch <kbusch@kernel.org>
Cc: Chao Leng <lengchao@huawei.com>, Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Sagi Grimberg <sagi@grimberg.me>,
Bart Van Assche <bvanassche@acm.org>,
Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Subject: Re: [PATCH V2 1/2] blk-mq: serialize queue quiesce and unquiesce by mutex
Date: Thu, 27 Aug 2020 10:38:44 +0800 [thread overview]
Message-ID: <20200827023844.GA129685@T590> (raw)
In-Reply-To: <20200826153633.GA2151118@dhcp-10-100-145-180.wdl.wdc.com>
On Wed, Aug 26, 2020 at 08:36:33AM -0700, Keith Busch wrote:
> On Wed, Aug 26, 2020 at 04:54:22PM +0800, Ming Lei wrote:
> > On Wed, Aug 26, 2020 at 03:51:25PM +0800, Chao Leng wrote:
> > > It doesn't matter. Because the reentry of quiesce&unquiesce queue is not
> > > safe, must be avoided by other mechanism. otherwise, exceptions may
> > > occur. Introduce mq_quiesce_lock looks saving possible synchronization
> > > waits, but it should not happen. If really happen, we need fix it.
> >
> > Sagi mentioned there may be nested queue quiesce, so I add .mq_quiesce_lock
> > to make this usage easy to support, meantime avoid percpu_ref warning
> > in such usage.
> >
> > Anyway, not see any problem with adding .mq_quiesce_lock, so I'd suggest to
> > move on with this way.
>
> I'm not sure there really are any nested queue quiesce paths, but if
> there are, wouldn't we need to track the "depth" like how a queue freeze
> works?
Both atomic 'depth' and .mq_quiesce_lock can work for nested queue
quiesce since we can avoid unnecessary queue quiesce with the mutex.
percpu_ref_kill() / percpu_ref_kill_and_confirm() can warn if the
percpu_ref has been killed, that is why I think Sagi's suggestion is good.
But 'depth' may cause trouble easily, such as unbalanced quiesce/unquiesce,
however no such issue with mutex, at least we don't require the two to
be paired strictly so far.
Thanks,
Ming
next prev parent reply other threads:[~2020-08-27 2:39 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-25 14:17 [PATCH V2 0/2] blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING Ming Lei
2020-08-25 14:17 ` [PATCH V2 1/2] blk-mq: serialize queue quiesce and unquiesce by mutex Ming Lei
2020-08-26 7:51 ` Chao Leng
2020-08-26 8:54 ` Ming Lei
2020-08-26 15:36 ` Keith Busch
2020-08-26 16:23 ` Sagi Grimberg
2020-08-27 2:38 ` Ming Lei [this message]
2020-08-25 14:17 ` [PATCH V2 2/2] blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING Ming Lei
2020-09-02 3:11 ` [PATCH V2 0/2] " Ming Lei
2020-09-02 17:52 ` Jens Axboe
2020-09-02 18:20 ` Sagi Grimberg
2020-09-03 0:41 ` Ming Lei
2020-09-03 0:35 ` Ming Lei
2020-09-03 12:37 ` Keith Busch
2020-09-03 13:10 ` Ming Lei
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