linux-kernel - Re: [patch 12/12] mm: correctly synchronize rss-counters at exit/exec

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Message-ID: <20120608170152.GA30975@redhat.com>
Date:	Fri, 8 Jun 2012 19:01:52 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	"kamezawa.hiroyu@...fujitsu.com" <kamezawa.hiroyu@...fujitsu.com>,
	"markus@...ppelsdorf.de" <markus@...ppelsdorf.de>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [patch 12/12] mm: correctly synchronize rss-counters at
	exit/exec

On 06/08, Konstantin Khlebnikov wrote:
>
> Oleg Nesterov wrote:
>> On 06/08, Konstantin Khlebnikov wrote:
>>>
>>> As result you can see "BUG: Bad rss-counter state mm:ffff88040783a680 idx:1 val:-1" in dmesg
>>>
>>> There left only one problem: nobody calls sync_mm_rss() after put_user() in mm_release().
>>
>> Both callers call sync_mm_rss() to make check_mm() happy. But please
>> see the changelog, I think we should move it into mm_release(). See
>> the patch below (on top of v2 I sent). I need to recheck.
>
> Patch below broken: it removes one hunk from kernel/exit.c twice.
> And it does not add anything into mm_release().

Yes, sorry. But I guess you understand the intent, mm_release() should
simply do sync_mm_rss() after put_user(clear_child_tid) unconditionally.

If task->mm == NULL but task->rss_stat, then there is something wrong
and probably OOPS makes sense.

Oleg.

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