linux-kernel - Re: [PATCH] cgroup/cpuset: Fix a race between cpuset

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Date:   Mon, 14 Feb 2022 09:50:39 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Zhang Qiao <zhangqiao22@...wei.com>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        lizefan.x@...edance.com, hannes@...xchg.org, matthltc@...ibm.com,
        bblum@...gle.com, menage@...gle.com, akpm@...ux-foundation.org,
        longman@...hat.com, mkoutny@...e.com, zhaogongyi@...wei.com
Subject: Re: [PATCH] cgroup/cpuset: Fix a race between cpuset_attach() and
 cpu hotplug

On Fri, Jan 21, 2022 at 06:12:10PM +0800, Zhang Qiao wrote:
> As previously discussed(https://lkml.org/lkml/2022/1/20/51),
> cpuset_attach() is affected with similar cpu hotplug race,
> as follow scenario:
> 
>      cpuset_attach()				cpu hotplug
>     ---------------------------            ----------------------
>     down_write(cpuset_rwsem)
>     guarantee_online_cpus() // (load cpus_attach)
> 					sched_cpu_deactivate
> 					  set_cpu_active()
> 					  // will change cpu_active_mask
>     set_cpus_allowed_ptr(cpus_attach)
>       __set_cpus_allowed_ptr_locked()
>        // (if the intersection of cpus_attach and
>          cpu_active_mask is empty, will return -EINVAL)
>     up_write(cpuset_rwsem)
> 
> To avoid races such as described above, protect cpuset_attach() call
> with cpu_hotplug_lock.
> 
> Fixes: be367d099270 ("cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time")
> Reported-by: Zhao Gongyi <zhaogongyi@...wei.com>
> Signed-off-by: Zhang Qiao <zhangqiao22@...wei.com>

Applied to cgroup/for-5.17-fixes w/ stable cc'd.

Thanks and sorry about the delay.

-- 
tejun