From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757983Ab0CaB5V (ORCPT ); Tue, 30 Mar 2010 21:57:21 -0400 Received: from mail-pw0-f46.google.com ([209.85.160.46]:57960 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757262Ab0CaB5T convert rfc822-to-8bit (ORCPT ); Tue, 30 Mar 2010 21:57:19 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=GToX+JCKcS7z8dlcv/3a/x9/fjVBWoaFHOf+fnsveyk7uELJp9oKSox6sJrCvDVLs0 7Hpk437fFE7JjLGkvIahpc3KKalg3IOxEg5R501b8s2dleX0N6VRv4pxW6RtKDZ0JnWh CQGDj/VnIBfHkBWX6/F9E5xt/8PJWYJA8c0MQ= MIME-Version: 1.0 In-Reply-To: <20100331094124.43c49290.kamezawa.hiroyu@jp.fujitsu.com> References: <20100316170808.GA29400@redhat.com> <20100330135634.09e6b045.akpm@linux-foundation.org> <20100331092815.c8b9d89c.kamezawa.hiroyu@jp.fujitsu.com> <20100330173721.cbd442cb.akpm@linux-foundation.org> <20100331094124.43c49290.kamezawa.hiroyu@jp.fujitsu.com> Date: Wed, 31 Mar 2010 10:57:18 +0900 Message-ID: Subject: Re: [PATCH] exit: fix oops in sync_mm_rss From: Minchan Kim To: KAMEZAWA Hiroyuki Cc: Andrew Morton , "Michael S. Tsirkin" , cl@linux-foundation.org, lee.schermerhorn@hp.com, rientjes@google.com, Hugh Dickins , Rik van Riel , Andrea Arcangeli , "David S. Miller" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Troels Liebe Bentsen , linux-bluetooth@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 31, 2010 at 9:41 AM, KAMEZAWA Hiroyuki wrote: > On Tue, 30 Mar 2010 17:37:21 -0400 > Andrew Morton wrote: > >> On Wed, 31 Mar 2010 09:28:15 +0900 KAMEZAWA Hiroyuki wrote: >> >> > On Tue, 30 Mar 2010 13:56:34 -0700 >> > Andrew Morton wrote: >> > >> > > That new BUG_ON() is triggering in Troels's machine when a bluetooth >> > > keyboard is enabled or disabled.  See >> > > (https://bugzilla.kernel.org/show_bug.cgi?id=15648. >> > > >> > > I guess the question is: how did a kernel thread get a non-zero >> > > task->rss_stat.count[i]?  If that's expected and OK then we will need >> > > to take some kernel-thread-avoidance action there. >> > > >> > It seems my fault that it's not initialized to be 0 at do_fork(), copy_process. >> > >> > About do_exit, do_exit() does this check. So, tsk->mm can be NULL. >> > >> >  949         if (group_dead) { >> >  950                 hrtimer_cancel(&tsk->signal->real_timer); >> >  951                 exit_itimers(tsk->signal); >> >  952                 if (tsk->mm) >> >  953                         setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm); >> >  954         } >> > >> > > Could whoever fixes this please also make __sync_task_rss_stat() >> > > static. >> > > >> > Ah, yes. I should do so. >> > >> > > I'll toss this over to Rafael/Maciej for tracking as a post-2.6.33 >> > > regression. >> > > >> > > Thanks. >> > > >> > >> > >> > == >> > >> > task->rss_stat wasn't initialized to 0 at copy_process(). >> > at exit, tsk->mm may be NULL. >> > And __sync_task_rss_stat() should be static. >> > >> > Signed-off-by: KAMEZAWA Hiroyuki >> > --- >> >  kernel/exit.c |    3 ++- >> >  kernel/fork.c |    3 +++ >> >  mm/memory.c   |    2 +- >> >  3 files changed, 6 insertions(+), 2 deletions(-) >> > >> > Index: mmotm-2.6.34-Mar24/kernel/exit.c >> > =================================================================== >> > --- mmotm-2.6.34-Mar24.orig/kernel/exit.c >> > +++ mmotm-2.6.34-Mar24/kernel/exit.c >> > @@ -950,7 +950,8 @@ NORET_TYPE void do_exit(long code) >> > >> >     acct_update_integrals(tsk); >> >     /* sync mm's RSS info before statistics gathering */ >> > -   sync_mm_rss(tsk, tsk->mm); >> > +   if (tsk->mm) >> > +           sync_mm_rss(tsk, tsk->mm); >> >     group_dead = atomic_dec_and_test(&tsk->signal->live); >> >     if (group_dead) { >> >             hrtimer_cancel(&tsk->signal->real_timer); >> > Index: mmotm-2.6.34-Mar24/mm/memory.c >> > =================================================================== >> > --- mmotm-2.6.34-Mar24.orig/mm/memory.c >> > +++ mmotm-2.6.34-Mar24/mm/memory.c >> > @@ -124,7 +124,7 @@ core_initcall(init_zero_pfn); >> > >> >  #if defined(SPLIT_RSS_COUNTING) >> > >> > -void __sync_task_rss_stat(struct task_struct *task, struct mm_struct *mm) >> > +static void __sync_task_rss_stat(struct task_struct *task, struct mm_struct *mm) >> >  { >> >     int i; >> > >> > Index: mmotm-2.6.34-Mar24/kernel/fork.c >> > =================================================================== >> > --- mmotm-2.6.34-Mar24.orig/kernel/fork.c >> > +++ mmotm-2.6.34-Mar24/kernel/fork.c >> > @@ -1060,6 +1060,9 @@ static struct task_struct *copy_process( >> >     p->prev_utime = cputime_zero; >> >     p->prev_stime = cputime_zero; >> >  #endif >> > +#if defined(SPLIT_RSS_COUNTING) >> > +   memset(&p->rss_stat, 0, sizeof(p->rss_stat)); >> > +#endif >> > >> >     p->default_timer_slack_ns = current->timer_slack_ns; >> >> OK, so the kenrel thread inherited a non-zero rss_stat from a userspace >> parent? >> > I think so. > >> With this fixed, the test for non-zero tsk->mm is't really needed in >> do_exit(), is it?  I guess it makes sense though - sync_mm_rss() only >> really works for kernel threads by luck.. > > At first, I considered so, too. But I changed my mind to show > "we know tsk->mm can be NULL here!" by code. > Because __sync_mm_rss_stat() has BUG_ON(!mm), the code reader will think > tsk->mm shouldn't be NULL always. > > Doesn't make sense ? > Nitpick. How about moving sync_mm_rss into after check !mm of exit_mm? -- Kind regards, Minchan Kim