Date:	Wed, 23 May 2012 10:07:42 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Martin Mokrejs <mmokrejs@...d.natur.cuni.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	"markus@...ppelsdorf.de" <markus@...ppelsdorf.de>,
	"hughd@...gle.com" <hughd@...gle.com>,
	"kamezawa.hiroyu@...fujitsu.com" <kamezawa.hiroyu@...fujitsu.com>,
	"oleg@...hat.com" <oleg@...hat.com>, Michal Hocko <mhocko@...e.cz>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: 3.4-rc7: BUG: Bad rss-counter state mm:ffff88040b56f800 idx:1
 val:-59

Andrew Morton wrote:
> On Wed, 23 May 2012 00:41:28 +0200
> Martin Mokrejs<mmokrejs@...d.natur.cuni.cz>  wrote:
>
>> Hi Andrew,
>>    while shutting down my laptop (Dell Vostro 3550 with 16GB RAM, core i7) with 3.4-rc7 I got:
>>
>> May 23 00:07:54 vostro kernel: [352687.968267] BUG: Bad rss-counter state mm:ffff88040b56f800 idx:1 val:-59
>> May 23 00:07:54 vostro kernel: [352687.968312] BUG: Bad rss-counter state mm:ffff88040b56f800 idx:2 val:59
>> May 23 00:07:55 vostro acpid: exiting
>> May 23 00:07:55 vostro syslog-ng[2838]: syslog-ng shutting down; version='3.3.4'
>>
>>    I found by Google the below thread and thought that maybe it is related?
>> http://comments.gmane.org/gmane.linux.kernel.mm/76459
>>
>> ...
>>
>
>
> Well hopefully the below will fix this?
>
> I notice that I don't have this tagged for -stable backporting.  That
> seems wrong.  Konstantin, do we know for how long this bug has been in
> there?

It there for years, by itself it is mostly harmless.
This warning was added in c3f0327f8e9d7a503f0d64573c311eddd61f197d
so only v3.4 has this, I thought this fix will be there before release.

>
>
>
> From: Konstantin Khlebnikov<khlebnikov@...nvz.org>
> Subject: mm: correctly synchronize rss-counters at exit/exec
>
> mm->rss_stat counters have per-task delta: task->rss_stat.  Before
> changing task->mm pointer the kernel must flush this delta with
> sync_mm_rss().
>
> do_exit() already calls sync_mm_rss() to flush the rss-counters before
> committing the rss statistics into task->signal->maxrss, taskstats, audit
> and other stuff.  Unfortunately the kernel does this before calling
> mm_release(), which can call put_user() for processing
> task->clear_child_tid.  So at this point we can trigger page-faults and
> task->rss_stat becomes non-zero again.  As a result mm->rss_stat becomes
> inconsistent and check_mm() will print something like this:
>
> | BUG: Bad rss-counter state mm:ffff88020813c380 idx:1 val:-1
> | BUG: Bad rss-counter state mm:ffff88020813c380 idx:2 val:1
>
> This patch moves sync_mm_rss() into mm_release(), and moves mm_release()
> out of do_exit() and calls it earlier.  After mm_release() there should be
> no pagefaults.
>
> [akpm@...ux-foundation.org: tweak comment]
> Signed-off-by: Konstantin Khlebnikov<khlebnikov@...nvz.org>
> Reported-by: Markus Trippelsdorf<markus@...ppelsdorf.de>
> Cc: Hugh Dickins<hughd@...gle.com>
> Cc: KAMEZAWA Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
> Cc: Oleg Nesterov<oleg@...hat.com>
> Signed-off-by: Andrew Morton<akpm@...ux-foundation.org>
> ---
>
>   fs/exec.c     |    1 -
>   kernel/exit.c |   13 ++++++++-----
>   kernel/fork.c |    8 ++++++++
>   3 files changed, 16 insertions(+), 6 deletions(-)
>
> diff -puN fs/exec.c~mm-correctly-synchronize-rss-counters-at-exit-exec fs/exec.c
> --- a/fs/exec.c~mm-correctly-synchronize-rss-counters-at-exit-exec
> +++ a/fs/exec.c
> @@ -823,7 +823,6 @@ static int exec_mmap(struct mm_struct *m
>   	/* 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);
>
>   	if (old_mm) {
> diff -puN kernel/exit.c~mm-correctly-synchronize-rss-counters-at-exit-exec kernel/exit.c
> --- a/kernel/exit.c~mm-correctly-synchronize-rss-counters-at-exit-exec
> +++ a/kernel/exit.c
> @@ -423,6 +423,7 @@ void daemonize(const char *name, ...)
>   	 * user space pages.  We don't need them, and if we didn't close them
>   	 * they would be locked into memory.
>   	 */
> +	mm_release(current, current->mm);
>   	exit_mm(current);
>   	/*
>   	 * We don't want to get frozen, in case system-wide hibernation
> @@ -640,7 +641,6 @@ static void exit_mm(struct task_struct *
>   	struct mm_struct *mm = tsk->mm;
>   	struct core_state *core_state;
>
> -	mm_release(tsk, mm);
>   	if (!mm)
>   		return;
>   	/*
> @@ -959,9 +959,13 @@ void do_exit(long code)
>   				preempt_count());
>
>   	acct_update_integrals(tsk);
> -	/* sync mm's RSS info before statistics gathering */
> -	if (tsk->mm)
> -		sync_mm_rss(tsk->mm);
> +
> +	/* Set exit_code before complete_vfork_done() in mm_release() */
> +	tsk->exit_code = code;
> +
> +	/* Release mm and sync mm's RSS info before statistics gathering */
> +	mm_release(tsk, tsk->mm);
> +
>   	group_dead = atomic_dec_and_test(&tsk->signal->live);
>   	if (group_dead) {
>   		hrtimer_cancel(&tsk->signal->real_timer);
> @@ -974,7 +978,6 @@ void do_exit(long code)
>   		tty_audit_exit();
>   	audit_free(tsk);
>
> -	tsk->exit_code = code;
>   	taskstats_exit(tsk, group_dead);
>
>   	exit_mm(tsk);
> diff -puN kernel/fork.c~mm-correctly-synchronize-rss-counters-at-exit-exec kernel/fork.c
> --- a/kernel/fork.c~mm-correctly-synchronize-rss-counters-at-exit-exec
> +++ a/kernel/fork.c
> @@ -809,6 +809,14 @@ void mm_release(struct task_struct *tsk,
>   		}
>   		tsk->clear_child_tid = NULL;
>   	}
> +
> +	/*
> +	 * Final rss-counter synchronization. After this point there must be
> +	 * no pagefaults into this mm from the current context.  Otherwise
> +	 * mm->rss_stat will be inconsistent.
> +	 */
> +	if (mm)
> +		sync_mm_rss(mm);
>   }
>
>   /*
> _
>

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