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From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	Balbir Singh <balbir@linux.vnet.ibm.com>
Subject: Re: [BUGFIX] memcg: avoid deadlock between move charge and try_charge()
Date: Wed, 17 Nov 2010 09:11:35 +0900	[thread overview]
Message-ID: <20101117091135.1d811e89.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <20101116191748.d6645376.nishimura@mxp.nes.nec.co.jp>

On Tue, 16 Nov 2010 19:17:48 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> 
> __mem_cgroup_try_charge() can be called under down_write(&mmap_sem)(e.g.
> mlock does it). This means it can cause deadlock if it races with move charge:
> 
> Ex.1)
>                 move charge             |        try charge
>   --------------------------------------+------------------------------
>     mem_cgroup_can_attach()             |  down_write(&mmap_sem)
>       mc.moving_task = current          |    ..
>       mem_cgroup_precharge_mc()         |  __mem_cgroup_try_charge()
>         mem_cgroup_count_precharge()    |    prepare_to_wait()
>           down_read(&mmap_sem)          |    if (mc.moving_task)
>           -> cannot aquire the lock     |    -> true
>                                         |      schedule()
> 
> Ex.2)
>                 move charge             |        try charge
>   --------------------------------------+------------------------------
>     mem_cgroup_can_attach()             |
>       mc.moving_task = current          |
>       mem_cgroup_precharge_mc()         |
>         mem_cgroup_count_precharge()    |
>           down_read(&mmap_sem)          |
>           ..                            |
>           up_read(&mmap_sem)            |
>                                         |  down_write(&mmap_sem)
>     mem_cgroup_move_task()              |    ..
>       mem_cgroup_move_charge()          |  __mem_cgroup_try_charge()
>         down_read(&mmap_sem)            |    prepare_to_wait()
>         -> cannot aquire the lock       |    if (mc.moving_task)
>                                         |    -> true
>                                         |      schedule()
> 
> To avoid this deadlock, we do all the move charge works (both can_attach() and
> attach()) under one mmap_sem section.
> And after this patch, we set/clear mc.moving_task outside mc.lock, because we
> use the lock only to check mc.from/to.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> Cc: <stable@kernel.org>

Thanks,
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>


WARNING: multiple messages have this Message-ID (diff)
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	Balbir Singh <balbir@linux.vnet.ibm.com>
Subject: Re: [BUGFIX] memcg: avoid deadlock between move charge and try_charge()
Date: Wed, 17 Nov 2010 09:11:35 +0900	[thread overview]
Message-ID: <20101117091135.1d811e89.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <20101116191748.d6645376.nishimura@mxp.nes.nec.co.jp>

On Tue, 16 Nov 2010 19:17:48 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> 
> __mem_cgroup_try_charge() can be called under down_write(&mmap_sem)(e.g.
> mlock does it). This means it can cause deadlock if it races with move charge:
> 
> Ex.1)
>                 move charge             |        try charge
>   --------------------------------------+------------------------------
>     mem_cgroup_can_attach()             |  down_write(&mmap_sem)
>       mc.moving_task = current          |    ..
>       mem_cgroup_precharge_mc()         |  __mem_cgroup_try_charge()
>         mem_cgroup_count_precharge()    |    prepare_to_wait()
>           down_read(&mmap_sem)          |    if (mc.moving_task)
>           -> cannot aquire the lock     |    -> true
>                                         |      schedule()
> 
> Ex.2)
>                 move charge             |        try charge
>   --------------------------------------+------------------------------
>     mem_cgroup_can_attach()             |
>       mc.moving_task = current          |
>       mem_cgroup_precharge_mc()         |
>         mem_cgroup_count_precharge()    |
>           down_read(&mmap_sem)          |
>           ..                            |
>           up_read(&mmap_sem)            |
>                                         |  down_write(&mmap_sem)
>     mem_cgroup_move_task()              |    ..
>       mem_cgroup_move_charge()          |  __mem_cgroup_try_charge()
>         down_read(&mmap_sem)            |    prepare_to_wait()
>         -> cannot aquire the lock       |    if (mc.moving_task)
>                                         |    -> true
>                                         |      schedule()
> 
> To avoid this deadlock, we do all the move charge works (both can_attach() and
> attach()) under one mmap_sem section.
> And after this patch, we set/clear mc.moving_task outside mc.lock, because we
> use the lock only to check mc.from/to.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> Cc: <stable@kernel.org>

Thanks,
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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  parent reply	other threads:[~2010-11-17  0:17 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-11-16 10:17 [BUGFIX] memcg: avoid deadlock between move charge and try_charge() Daisuke Nishimura
2010-11-16 10:17 ` Daisuke Nishimura
2010-11-16 20:41 ` Andrew Morton
2010-11-16 20:41   ` Andrew Morton
2010-11-17  0:24   ` Daisuke Nishimura
2010-11-17  0:24     ` Daisuke Nishimura
2010-11-26  7:48     ` [stable][BUGFIX] " Daisuke Nishimura
2010-11-26  7:48       ` Daisuke Nishimura
2010-12-06 22:46       ` [stable] [BUGFIX] " Greg KH
2010-12-06 22:46         ` Greg KH
2010-11-17  0:11 ` KAMEZAWA Hiroyuki [this message]
2010-11-17  0:11   ` KAMEZAWA Hiroyuki

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