linux-kernel - Re: [PATCH] exit: fix oops in sync_mm

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Date:	Wed, 31 Mar 2010 11:12:02 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Michael S. Tsirkin" <mst@...hat.com>, cl@...ux-foundation.org,
	lee.schermerhorn@...com, rientjes@...gle.com,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"David S. Miller" <davem@...emloft.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Troels Liebe Bentsen <tlb@...anden.dk>,
	linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH] exit: fix oops in sync_mm_rss

On Wed, 31 Mar 2010 10:57:18 +0900
Minchan Kim <minchan.kim@...il.com> wrote:

> On Wed, Mar 31, 2010 at 9:41 AM, KAMEZAWA Hiroyuki

> > Doesn't make sense ?
> >
> 
> Nitpick.
> How about moving sync_mm_rss into after check !mm of exit_mm?
> 
Hmm.
==
        sync_mm_rss(tsk, tsk->mm);
        group_dead = atomic_dec_and_test(&tsk->signal->live);
        if (group_dead) {
                hrtimer_cancel(&tsk->signal->real_timer);
                exit_itimers(tsk->signal);
                if (tsk->mm)
                        setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm); ---(**)
        }
        acct_collect(code, group_dead);
        if (group_dead)
                tty_audit_exit();
        if (unlikely(tsk->audit_context))
                audit_free(tsk);

        tsk->exit_code = code;
        taskstats_exit(tsk, group_dead); --------(*)
	
        exit_mm(tsk);
==
task_acct routine has to handle mm information (*).
So, we have to sync somewhere before exit_mm() or tsk->mm goes to NULL.

I think taskstat is an only acct hook which gatheres mm's rss information
but I placed sync_mm_rss() before all accounting routine.
Anyway, sync_mm_rss() should be before (**)
setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);

Thanks,
-Kame 




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