Re: 3.4-rc7: BUG: Bad rss-counter state mm:ffff88040b56f800 idx:1 val:-59

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

Martin Mokrejs wrote:
> Hi,
>    I rebooted the laptop twice today after just brief uses and the messages did not
> appear in the logs.
>
> Now I just applied the below patch and during two reboots it did not appear either.
> Do I have to use the computer for some longer while to reproduce the issue? ;-)

Yes, some data must be in swap to reproduce this, so memory pressure required here.

>
> I will stay with the patch applied over 3.4-rc7 and would the BUG: re-appear I will
> let you know. But I doubt at the moment I could confirm it really helped.
> Clues how to reproduce? ;)
> Martin
>
> Andrew Morton wrote:
>> On Wed, 23 May 2012 00:41:28 +0200
>> Martin Mokrejs<mmokrejs@fold.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?
>>
>>
>>
>> From: Konstantin Khlebnikov<khlebnikov@openvz.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@linux-foundation.org: tweak comment]
>> Signed-off-by: Konstantin Khlebnikov<khlebnikov@openvz.org>
>> Reported-by: Markus Trippelsdorf<markus@trippelsdorf.de>
>> Cc: Hugh Dickins<hughd@google.com>
>> Cc: KAMEZAWA Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com>
>> Cc: Oleg Nesterov<oleg@redhat.com>
>> Signed-off-by: Andrew Morton<akpm@linux-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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