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From: Tejun Heo <tj@kernel.org>
To: Qais Yousef <qais.yousef@arm.com>
Cc: Li Zefan <lizefan@huawei.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cgroup/cpuset: Fix a race condition when reading cpuset.*
Date: Wed, 12 Feb 2020 17:15:43 -0500	[thread overview]
Message-ID: <20200212221543.GL80993@mtj.thefacebook.com> (raw)
In-Reply-To: <20200211141554.24181-1-qais.yousef@arm.com>

On Tue, Feb 11, 2020 at 02:15:54PM +0000, Qais Yousef wrote:
> LTP cpuset_hotplug_test.sh was failing with the following error message
> 
> 	cpuset_hotplug 1 TFAIL: root group's cpus isn't expected(Result: 0-5, Expect: 0,2-5).
> 
> Which is due to a race condition between cpu hotplug operation and
> reading cpuset.cpus file.
> 
> When a cpu is onlined/offlined, cpuset schedules a workqueue to sync its
> internal data structures with the new values. If a read happens during
> this window, the user will read a stale value, hence triggering the
> failure above.
> 
> To fix the issue make sure cpuset_wait_for_hotplug() is called before
> allowing any value to be read, hence forcing the synchronization to
> happen before the read.
> 
> I ran 500 iterations with this fix applied with no failure triggered.
> 
> Signed-off-by: Qais Yousef <qais.yousef@arm.com>

Hello, Qais. I just applied a patch which makes the operation
synchronous. Can you see whether the problem is gone on the
cgroup/for-next branch?

  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next

Thanks.

-- 
tejun

  reply	other threads:[~2020-02-12 22:15 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11 14:15 [PATCH] cgroup/cpuset: Fix a race condition when reading cpuset.* Qais Yousef
2020-02-12 22:15 ` Tejun Heo [this message]
2020-02-13 11:50   ` Qais Yousef
2020-02-13 13:56     ` Tejun Heo
2020-02-13 14:36       ` Qais Yousef

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