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

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

Oleg Nesterov wrote:
> On 06/07, Konstantin Khlebnikov wrote:
>>
>> Oleg Nesterov wrote:
>>>
>>> I'll write the changelog and send the patch tomorrow.
>>
>> Ding! Week is over, or I missed something? )
>
> Pong ;)
>
> I have sent the patch on May 31, see
> http://marc.info/?l=linux-kernel&m=133848759505805
> Also attached below, just in case.
>
> Initiallly I sent 2 patches, see
> http://marc.info/?l=linux-kernel&m=133848784705941
> but 2/2 (your patch) was already merged.

Hmm, ok. Thanks.

I think rss-fix must be in stable-3.4.x -- that "BUG..." message can disturb users.
Plus via this bug any application can decrease rss down to zero =)

>
> -------------------------------------------------------------------------------
> [PATCH] correctly synchronize rss-counters at exit/exec
>
> A simplified version of Konstantin Khlebnikov's patch.
>
> do_exit() and exec_mmap() call sync_mm_rss() before mm_release()
> does put_user(clear_child_tid) which can update task->rss_stat
> and thus make mm->rss_stat inconsistent. This triggers the "BUG:"
> printk in check_mm().
>
> - Move the final sync_mm_rss() from do_exit() to exit_mm(), and
>    change exec_mmap() to call sync_mm_rss() after mm_release() to
>    make check_mm() happy.
>
>    Perhaps we should simply move it into mm_release() and call it
>    unconditionally to catch the "task->rss_stat != 0&&  !task->mm"
>    bugs.
>
> - Since taskstats_exit() is called before exit_mm(), add another
>    sync_mm_rss() into xacct_add_tsk() who actually uses rss_stat.
>
>    Probably we should also shift acct_update_integrals().
>
> Reported-by: Markus Trippelsdorf<markus@trippelsdorf.de>
> Tested-by: Martin Mokrejs<mmokrejs@fold.natur.cuni.cz>
> Signed-off-by: Oleg Nesterov<oleg@redhat.com>
> Acked-by: Konstantin Khlebnikov<khlebnikov@openvz.org>
> ---
>   fs/exec.c       |    2 +-
>   kernel/exit.c   |    5 ++---
>   kernel/tsacct.c |    1 +
>   3 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 52c9e2f..e49e3c2 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -823,10 +823,10 @@ static int exec_mmap(struct mm_struct *mm)
>   	/* 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) {
> +		sync_mm_rss(old_mm);
>   		/*
>   		 * Make sure that if there is a core dump in progress
>   		 * for the old mm, we get out and die instead of going
> diff --git a/kernel/exit.c b/kernel/exit.c
> index ab972a7..b3a84b5 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -655,6 +655,8 @@ static void exit_mm(struct task_struct * tsk)
>   	mm_release(tsk, mm);
>   	if (!mm)
>   		return;
> +
> +	sync_mm_rss(mm);
>   	/*
>   	 * Serialize with any possible pending coredump.
>   	 * We must hold mmap_sem around checking core_state
> @@ -965,9 +967,6 @@ 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);
>   	group_dead = atomic_dec_and_test(&tsk->signal->live);
>   	if (group_dead) {
>   		hrtimer_cancel(&tsk->signal->real_timer);
> diff --git a/kernel/tsacct.c b/kernel/tsacct.c
> index 23b4d78..a64ee90 100644
> --- a/kernel/tsacct.c
> +++ b/kernel/tsacct.c
> @@ -91,6 +91,7 @@ void xacct_add_tsk(struct taskstats *stats, struct task_struct *p)
>   	stats->virtmem = p->acct_vm_mem1 * PAGE_SIZE / MB;
>   	mm = get_task_mm(p);
>   	if (mm) {
> +		sync_mm_rss(mm);
>   		/* adjust to KB unit */
>   		stats->hiwater_rss   = get_mm_hiwater_rss(mm) * PAGE_SIZE / KB;
>   		stats->hiwater_vm    = get_mm_hiwater_vm(mm)  * PAGE_SIZE / KB;

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