linux-kernel - Re: [PATCH] [BUGFIX] update mm->owner even if no next owner.

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Message-ID: <BANLkTikJONQ2tL_L=QtMv9qsOmJj3dD+Rg@mail.gmail.com>
Date:	Sun, 12 Jun 2011 08:04:21 +0900
From:	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ying Han <yinghan@...gle.com>, Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH] [BUGFIX] update mm->owner even if no next owner.

2011/6/12 Andrea Arcangeli <aarcange@...hat.com>:
> On Sat, Jun 11, 2011 at 07:51:36PM +0200, Johannes Weiner wrote:
>> This is a problem with the patch, but I think Kame's analysis and
>> approach to fix it are still correct.
>
> I agree with Kame's analysis too. This explains why removing the
> mmap_sem read mode introduced the problem, it was quite some
> unexpected subtleness not apparent to the naked eye, as memcg didn't
> explicitly relay on mmap_sem but it did implicitly during exit because
> of the __khugepaged_exit waiting if we were collapsing an hugepage...
>
> So the fix is safe because the task struct is freed with
> delayed_put_task_struct and that won't run until we rcu_read_unlock
> after mem_cgroup_from_task.
>
> Reviewed-by: Andrea Arcangeli <aarcange@...hat.com>
>

Thank you all.

Regards,
-Kame
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