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From: "tj@kernel.org" <tj@kernel.org>
To: Bart Van Assche <Bart.VanAssche@wdc.com>
Cc: "hch@lst.de" <hch@lst.de>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"00moses.alexander00@gmail.com" <00moses.alexander00@gmail.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>
Subject: Re: [PATCH] block: Ensure that a request queue is dissociated from the cgroup controller
Date: Thu, 12 Apr 2018 11:11:21 -0700	[thread overview]
Message-ID: <20180412181121.GA1911913@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <f98af37ea6755119177c26fbb73b0071ddef90b8.camel@wdc.com>

Hello,

On Thu, Apr 12, 2018 at 04:29:09PM +0000, Bart Van Assche wrote:
> Any code that submits a bio or request needs blk_queue_enter() /
> blk_queue_exit() anyway. Please have a look at the following commit - you will
> see that that commit reduces the number of blk_queue_enter() / blk_queue_exit()
> calls in the hot path:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-linus&id=37f9579f4c31a6d698dbf3016d7bf132f9288d30

So, this can work, but it's still pretty fragile.

* Lock switching is fragile and we really should get rid of it.  This
  is very likely to come back and bite us.

* Right now, blk_queue_enter/exit() doesn't have any annotations.
  IOW, there's no way for paths which need enter locked to actually
  assert that.  If we're gonna protect more things with queue
  enter/exit, it gotta be annotated.

Thanks.

-- 
tejun

  reply	other threads:[~2018-04-12 18:11 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-12  1:58 [PATCH] block: Ensure that a request queue is dissociated from the cgroup controller Bart Van Assche
2018-04-12  4:20 ` Alexandru Moise
2018-04-12  4:32   ` Alexandru Moise
2018-04-12  4:22 ` Alexandru Moise
2018-04-12  5:34 ` Christoph Hellwig
2018-04-12 11:52   ` Bart Van Assche
2018-04-12 13:14     ` hch
2018-04-12 13:48       ` tj
2018-04-12 13:56         ` hch
2018-04-12 13:58           ` tj
2018-04-12 14:07             ` tj
2018-04-12 13:51 ` Tejun Heo
2018-04-12 14:09   ` Bart Van Assche
2018-04-12 15:37     ` Tejun Heo
2018-04-12 16:03       ` Bart Van Assche
2018-04-12 16:12         ` tj
2018-04-12 16:29           ` Bart Van Assche
2018-04-12 18:11             ` tj [this message]
2018-04-12 18:56               ` Bart Van Assche
2018-04-12 19:09                 ` tj
2018-04-12 22:40                   ` Bart Van Assche
2018-04-13 15:18                     ` tj

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