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

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Message-Id: <20100331092815.c8b9d89c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 31 Mar 2010 09:28:15 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"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>,
	Minchan Kim <minchan.kim@...il.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 Tue, 30 Mar 2010 13:56:34 -0700
Andrew Morton <akpm@...ux-foundation.org> 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 <kamezawa.hiroyu@...fujitsu.com>
---
 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;
 

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