Re: + make-get_user_pages-interruptible.patch added to -mm tree

Re: + make-get_user_pages-interruptible.patch added to -mm tree

[Oleg Nesterov]

Ying Han wrote:
>
> -static int sigkill_pending(struct task_struct *tsk)
> +int sigkill_pending(struct task_struct *tsk)
>  {
>  	return	sigismember(&tsk->pending.signal, SIGKILL) ||
>  		sigismember(&tsk->signal->shared_pending.signal, SIGKILL);
> diff -puN mm/memory.c~make-get_user_pages-interruptible mm/memory.c
> --- a/mm/memory.c~make-get_user_pages-interruptible
> +++ a/mm/memory.c
> @@ -1219,12 +1219,12 @@ int __get_user_pages(struct task_struct 
>  			struct page *page;
>
>  			/*
> -			 * If tsk is ooming, cut off its access to large memory
> -			 * allocations. It has a pending SIGKILL, but it can't
> -			 * be processed until returning to user space.
> +			 * If we have a pending SIGKILL, don't keep
> +			 * allocating memory.
>  			 */
> -			if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
> -				return i ? i : -ENOMEM;
> +			if (unlikely(sigkill_pending(current) ||
> +					sigkill_pending(tsk)))

Please do not export/use sigkill_pending(). It is "private" for ptrace_stop()
(and actually should die imho).

We have fatal_signal_pending() for that.

Oleg.

Re: + make-get_user_pages-interruptible.patch added to -mm tree

[Ying Han]

Thanks Oleg, i looked at the code again and this is a reasonable
change. I will make the change on the patch.
Andrew,
    should i make a patch based on current change or make the same
patch as [V6]?

thanks
--Ying

On Thu, Nov 27, 2008 at 12:04 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> Ying Han wrote:
>>
>> -static int sigkill_pending(struct task_struct *tsk)
>> +int sigkill_pending(struct task_struct *tsk)
>>  {
>>       return  sigismember(&tsk->pending.signal, SIGKILL) ||
>>               sigismember(&tsk->signal->shared_pending.signal, SIGKILL);
>> diff -puN mm/memory.c~make-get_user_pages-interruptible mm/memory.c
>> --- a/mm/memory.c~make-get_user_pages-interruptible
>> +++ a/mm/memory.c
>> @@ -1219,12 +1219,12 @@ int __get_user_pages(struct task_struct
>>                       struct page *page;
>>
>>                       /*
>> -                      * If tsk is ooming, cut off its access to large memory
>> -                      * allocations. It has a pending SIGKILL, but it can't
>> -                      * be processed until returning to user space.
>> +                      * If we have a pending SIGKILL, don't keep
>> +                      * allocating memory.
>>                        */
>> -                     if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
>> -                             return i ? i : -ENOMEM;
>> +                     if (unlikely(sigkill_pending(current) ||
>> +                                     sigkill_pending(tsk)))
>
> Please do not export/use sigkill_pending(). It is "private" for ptrace_stop()
> (and actually should die imho).
>
> We have fatal_signal_pending() for that.
>
> Oleg.
>
>

Re: + make-get_user_pages-interruptible.patch added to -mm tree

[Andrew Morton]

On Mon, 1 Dec 2008 15:00:14 -0800
Ying Han <yinghan@google.com> wrote:

> On Thu, Nov 27, 2008 at 12:04 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> > Ying Han wrote:
> >>
> >> -static int sigkill_pending(struct task_struct *tsk)
> >> +int sigkill_pending(struct task_struct *tsk)
> >>  {
> >>       return  sigismember(&tsk->pending.signal, SIGKILL) ||
> >>               sigismember(&tsk->signal->shared_pending.signal, SIGKILL);
> >> diff -puN mm/memory.c~make-get_user_pages-interruptible mm/memory.c
> >> --- a/mm/memory.c~make-get_user_pages-interruptible
> >> +++ a/mm/memory.c
> >> @@ -1219,12 +1219,12 @@ int __get_user_pages(struct task_struct
> >>                       struct page *page;
> >>
> >>                       /*
> >> -                      * If tsk is ooming, cut off its access to large memory
> >> -                      * allocations. It has a pending SIGKILL, but it can't
> >> -                      * be processed until returning to user space.
> >> +                      * If we have a pending SIGKILL, don't keep
> >> +                      * allocating memory.
> >>                        */
> >> -                     if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
> >> -                             return i ? i : -ENOMEM;
> >> +                     if (unlikely(sigkill_pending(current) ||
> >> +                                     sigkill_pending(tsk)))
> >
> > Please do not export/use sigkill_pending(). It is "private" for ptrace_stop()
> > (and actually should die imho).
> >
> > We have fatal_signal_pending() for that.
> >
> > Oleg.
> >

(top-posting repaired..)

> Thanks Oleg, i looked at the code again and this is a reasonable
> change. I will make the change on the patch.
> Andrew,
>     should i make a patch based on current change or make the same
> patch as [V6]?

I don't mind either way.  I guess a fresh new patch would simplify
review for everyone.

Note that fatal_signal_pending() is not an exact replacement for
sigkill_pending() - fatal_signal_pending() doesn't test the shared
pending signals.

Re: + make-get_user_pages-interruptible.patch added to -mm tree

[Ying Han]

thanks Andrew.


On Mon, Dec 1, 2008 at 3:09 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Mon, 1 Dec 2008 15:00:14 -0800
> Ying Han <yinghan@google.com> wrote:
>
>> On Thu, Nov 27, 2008 at 12:04 PM, Oleg Nesterov <oleg@redhat.com> wrote:
>> > Ying Han wrote:
>> >>
>> >> -static int sigkill_pending(struct task_struct *tsk)
>> >> +int sigkill_pending(struct task_struct *tsk)
>> >>  {
>> >>       return  sigismember(&tsk->pending.signal, SIGKILL) ||
>> >>               sigismember(&tsk->signal->shared_pending.signal, SIGKILL);
>> >> diff -puN mm/memory.c~make-get_user_pages-interruptible mm/memory.c
>> >> --- a/mm/memory.c~make-get_user_pages-interruptible
>> >> +++ a/mm/memory.c
>> >> @@ -1219,12 +1219,12 @@ int __get_user_pages(struct task_struct
>> >>                       struct page *page;
>> >>
>> >>                       /*
>> >> -                      * If tsk is ooming, cut off its access to large memory
>> >> -                      * allocations. It has a pending SIGKILL, but it can't
>> >> -                      * be processed until returning to user space.
>> >> +                      * If we have a pending SIGKILL, don't keep
>> >> +                      * allocating memory.
>> >>                        */
>> >> -                     if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
>> >> -                             return i ? i : -ENOMEM;
>> >> +                     if (unlikely(sigkill_pending(current) ||
>> >> +                                     sigkill_pending(tsk)))
>> >
>> > Please do not export/use sigkill_pending(). It is "private" for ptrace_stop()
>> > (and actually should die imho).
>> >
>> > We have fatal_signal_pending() for that.
>> >
>> > Oleg.
>> >
>
> (top-posting repaired..)
>
>> Thanks Oleg, i looked at the code again and this is a reasonable
>> change. I will make the change on the patch.
>> Andrew,
>>     should i make a patch based on current change or make the same
>> patch as [V6]?
>
> I don't mind either way.  I guess a fresh new patch would simplify
> review for everyone.
>
> Note that fatal_signal_pending() is not an exact replacement for
> sigkill_pending() - fatal_signal_pending() doesn't test the shared
> pending signals.
>
yeah, i noticed that and that is why i used the sigkill_pending
initially. But after a deeper look
at the signal code, i found for SIGKILL ( signal we care about in this
patch ), tsk->pending is a
superset of tsk->signal->shared_pending.


--Ying
>
>

Re: + make-get_user_pages-interruptible.patch added to -mm tree

[Oleg Nesterov]

On 12/01, Ying Han wrote:
>
> On Mon, Dec 1, 2008 at 3:09 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > Note that fatal_signal_pending() is not an exact replacement for
> > sigkill_pending() - fatal_signal_pending() doesn't test the shared
> > pending signals.
> >
> yeah, i noticed that and that is why i used the sigkill_pending
> initially. But after a deeper look
> at the signal code, i found for SIGKILL ( signal we care about in this
> patch ), tsk->pending is a
> superset of tsk->signal->shared_pending.

Yes. If we have SIGKILL in ->shared_pending, we must have it in
in ->pending too.

The only exception is when we send SIGKILL to the already dying task
which has already dequeued SIGKILL from ->pending. And we do have a
special case: coredumping. elf_core_dump() does get_user_pages()
when the process is "almost" dead, it has SIGNAL_GROUP_EXIT.

So, if get_user_pages() calls sigkill_pending() instead of
fatal_signal_pending(), this can help. But:

	- this relies on the fact that we always queue SIGKILL
	  even if the task is dead. This behaviour can be changed.

	- this doesn't stop the coredumping, it will continue
	  with DUMP_SEEK(). Yes, this is better if we want to
	  stop this thread to populate the memory, but I think
	  we should just fix the coredumping - it should be
	  interruptible.

Actually, the patch exists:
	http://marc.info/?l=linux-kernel&m=121665710711931

Oleg.