linux-kernel - Re: [PATCH] mm: sync rss-counters at the end of exit

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Date:	Tue, 10 Apr 2012 18:04:57 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: sync rss-counters at the end of exit_mm()

On 2012.04.10 at 10:34 +0400, Konstantin Khlebnikov wrote:
> Hugh Dickins wrote:
> > On Mon, 9 Apr 2012, KOSAKI Motohiro wrote:
> >> On Mon, Apr 9, 2012 at 4:03 PM, Konstantin Khlebnikov
> >> <khlebnikov@...nvz.org>  wrote:
> >>> On task's exit do_exit() calls sync_mm_rss() but this is not enough,
> >>> there can be page-faults after this point, for example exit_mm() ->
> >>> mm_release() ->  put_user() (for processing tsk->clear_child_tid).
> >>> Thus there may be some rss-counters delta in current->rss_stat.
> >>
> >> Seems reasonable.
> >
> > Yes, I think Konstantin has probably caught it;
> > but I'd like to hear confirmation from Markus.
> 
> There is another bug in exec_mmap()
> 
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -823,8 +823,8 @@ static int exec_mmap(struct mm_struct *mm)
>          /* Notify parent that we're no longer interested in the old VM */
>          tsk = current;
>          old_mm = current->mm;
> -       sync_mm_rss(old_mm);
>          mm_release(tsk, old_mm);
> +       sync_mm_rss(old_mm);
> 
>          if (old_mm) {
>                  /*

FWIW with both patches applied I cannot reproduce the issue anymore.

Thanks.

-- 
Markus
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