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From: Tejun Heo <tj@kernel.org>
To: Li Zefan <lizefan@huawei.com>
Cc: Oleg Nesterov <oleg@redhat.com>, anjana vk <anjanvk12@gmail.com>,
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
	eunki_kim@samsung.com
Subject: Re: [PATCH] cgroup: fix to break the while loop in cgroup_attach_task() correctly
Date: Sun, 13 Oct 2013 16:08:16 -0400	[thread overview]
Message-ID: <20131013200816.GE18075@htj.dyndns.org> (raw)
In-Reply-To: <5258BB05.8030106@huawei.com>

On Sat, Oct 12, 2013 at 10:59:17AM +0800, Li Zefan wrote:
> From: Anjana V Kumar <anjanavk12@gmail.com>
> 
> Both Anjana and Eunki reported a stall in the while_each_thread loop
> in cgroup_attach_task().
> 
> It's because, when we attach a single thread to a cgroup, if the cgroup
> is exiting or is already in that cgroup, we won't break the loop.
> 
> If the task is already in the cgroup, the bug can lead to another thread
> being attached to the cgroup unexpectedly:
> 
>   # echo 5207 > tasks
>   # cat tasks
>   5207
>   # echo 5207 > tasks
>   # cat tasks
>   5207
>   5215
> 
> What's worse, if the task to be attached isn't the leader of the thread
> group, we might never exit the loop, hence cpu stall. Thanks for Oleg's
> analysis.
> 
> This bug was introduced by commit 081aa458c38ba576bdd4265fc807fa95b48b9e79
> ("cgroup: consolidate cgroup_attach_task() and cgroup_attach_proc()")
> 
> Cc: <stable@vger.kernel.org> # 3.9+
> Reported-by: Eunki Kim <eunki_kim@samsung.com>
> Reported-by: Anjana V Kumar <anjanavk12@gmail.com>
> Signed-off-by: Anjana V Kumar <anjanavk12@gmail.com>
> [ lizf: - fixed the first continue, pointed out by Oleg,
>         - rewrote changelog. ]
> Signed-off-by: Li Zefan <lizefan@huawei.com>

Applied to cgroup/for-3.12-fixes.

Thanks.

-- 
tejun

WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Cc: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	anjana vk <anjanvk12-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	eunki_kim-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org
Subject: Re: [PATCH] cgroup: fix to break the while loop in cgroup_attach_task() correctly
Date: Sun, 13 Oct 2013 16:08:16 -0400	[thread overview]
Message-ID: <20131013200816.GE18075@htj.dyndns.org> (raw)
In-Reply-To: <5258BB05.8030106-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>

On Sat, Oct 12, 2013 at 10:59:17AM +0800, Li Zefan wrote:
> From: Anjana V Kumar <anjanavk12-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> 
> Both Anjana and Eunki reported a stall in the while_each_thread loop
> in cgroup_attach_task().
> 
> It's because, when we attach a single thread to a cgroup, if the cgroup
> is exiting or is already in that cgroup, we won't break the loop.
> 
> If the task is already in the cgroup, the bug can lead to another thread
> being attached to the cgroup unexpectedly:
> 
>   # echo 5207 > tasks
>   # cat tasks
>   5207
>   # echo 5207 > tasks
>   # cat tasks
>   5207
>   5215
> 
> What's worse, if the task to be attached isn't the leader of the thread
> group, we might never exit the loop, hence cpu stall. Thanks for Oleg's
> analysis.
> 
> This bug was introduced by commit 081aa458c38ba576bdd4265fc807fa95b48b9e79
> ("cgroup: consolidate cgroup_attach_task() and cgroup_attach_proc()")
> 
> Cc: <stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org> # 3.9+
> Reported-by: Eunki Kim <eunki_kim-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
> Reported-by: Anjana V Kumar <anjanavk12-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Anjana V Kumar <anjanavk12-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> [ lizf: - fixed the first continue, pointed out by Oleg,
>         - rewrote changelog. ]
> Signed-off-by: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>

Applied to cgroup/for-3.12-fixes.

Thanks.

-- 
tejun

  reply	other threads:[~2013-10-13 20:08 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-10-04  5:25 cgroup attach task - slogging cpu anjana vk
     [not found] ` <CALPf4Tz+Gf_Q7wKKBufCc1mtV1qVPVrOW0S1qhHxfOv6pJa2Kg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-10-04 13:02   ` Oleg Nesterov
     [not found]     ` <20131004130207.GA9338-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2013-10-07 18:45       ` Tejun Heo
     [not found]         ` <20131007184507.GD27396-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org>
2013-10-08 14:58           ` Oleg Nesterov
     [not found]             ` <20131008145833.GA15600-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2013-10-09  5:35               ` Li Zefan
     [not found]                 ` <5254EB2A.7090803-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2013-10-09 13:30                   ` Oleg Nesterov
     [not found]                     ` <20131009133047.GA12414-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2013-10-09 14:05                       ` Oleg Nesterov
2013-10-09 16:54                         ` cgroup_attach_task && while_each_thread (Was: cgroup attach task - slogging cpu) Oleg Nesterov
2013-10-09 16:54                           ` Oleg Nesterov
2013-10-11 13:15                           ` Li Zefan
2013-10-11 13:15                             ` Li Zefan
2013-10-11 16:00                             ` Oleg Nesterov
2013-10-11 16:00                               ` Oleg Nesterov
2013-10-12  2:59                               ` [PATCH] cgroup: fix to break the while loop in cgroup_attach_task() correctly Li Zefan
2013-10-12  2:59                                 ` Li Zefan
2013-10-13 20:08                                 ` Tejun Heo [this message]
2013-10-13 20:08                                   ` Tejun Heo
2013-10-15  5:04                               ` cgroup_attach_task && while_each_thread (Was: cgroup attach task - slogging cpu) anjana vk
2013-10-15  5:04                                 ` anjana vk
2013-10-15 13:34                                 ` Tejun Heo
2013-10-15 13:34                                   ` Tejun Heo
     [not found]                         ` <CAChhN7RerxpSadqyosUeSKFg+qcOpO4d-maEKBZ0rvOQGvN27g@mail.gmail.com>
     [not found]                           ` <CAChhN7RerxpSadqyosUeSKFg+qcOpO4d-maEKBZ0rvOQGvN27g-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-10-10  4:22                             ` cgroup attach task - slogging cpu anjana vk
2013-10-10 11:11                             ` Oleg Nesterov

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