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* [PATCH] sched: Fix get_push_task() vs migrate_disable()
@ 2021-08-26 13:37 Sebastian Andrzej Siewior
  2021-08-26 16:24 ` Tao Zhou
                   ` (2 more replies)
  0 siblings, 3 replies; 6+ messages in thread
From: Sebastian Andrzej Siewior @ 2021-08-26 13:37 UTC (permalink / raw)
  To: linux-kernel
  Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
	Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	Daniel Bristot de Oliveira, Thomas Gleixner

push_rt_task() attempts to move the currently running task away if the
next runnable task has migration disabled and therefore is pinned on the
current CPU.

The current task is retrieved via get_push_task() which only checks for
nr_cpus_allowed == 1, but does not check whether the task has migration
disabled and therefore cannot be moved either. The consequence is a
pointless invocation of the migration thread which correctly observes
that the task cannot be moved.

Return NULL if the task has migration disabled and cannot be moved to
another CPU.

Fixes: a7c81556ec4d3 ("sched: Fix migrate_disable() vs rt/dl balancing")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/sched/sched.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e205b63d6db07..32a4945730a9b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2259,6 +2259,9 @@ static inline struct task_struct *get_push_task(struct rq *rq)
 	if (p->nr_cpus_allowed == 1)
 		return NULL;
 
+	if (p->migration_disabled)
+		return NULL;
+
 	rq->push_busy = true;
 	return get_task_struct(p);
 }
-- 
2.33.0


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] sched: Fix get_push_task() vs migrate_disable()
  2021-08-26 13:37 [PATCH] sched: Fix get_push_task() vs migrate_disable() Sebastian Andrzej Siewior
@ 2021-08-26 16:24 ` Tao Zhou
  2021-08-26 19:38   ` Thomas Gleixner
  2021-08-26 16:56 ` Peter Zijlstra
  2021-08-26 17:07 ` [tip: sched/urgent] " tip-bot2 for Sebastian Andrzej Siewior
  2 siblings, 1 reply; 6+ messages in thread
From: Tao Zhou @ 2021-08-26 16:24 UTC (permalink / raw)
  To: Sebastian Andrzej Siewior, linux-kernel, tao.zhou
  Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
	Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	Daniel Bristot de Oliveira, Thomas Gleixner

Hi Sebastian,

On Thu, Aug 26, 2021 at 03:37:38PM +0200, Sebastian Andrzej Siewior wrote:

> push_rt_task() attempts to move the currently running task away if the
> next runnable task has migration disabled and therefore is pinned on the
> current CPU.
> 
> The current task is retrieved via get_push_task() which only checks for
> nr_cpus_allowed == 1, but does not check whether the task has migration
> disabled and therefore cannot be moved either. The consequence is a
> pointless invocation of the migration thread which correctly observes
> that the task cannot be moved.
> 
> Return NULL if the task has migration disabled and cannot be moved to
> another CPU.
> 
> Fixes: a7c81556ec4d3 ("sched: Fix migrate_disable() vs rt/dl balancing")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  kernel/sched/sched.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index e205b63d6db07..32a4945730a9b 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2259,6 +2259,9 @@ static inline struct task_struct *get_push_task(struct rq *rq)
>  	if (p->nr_cpus_allowed == 1)
>  		return NULL;
>  
> +	if (p->migration_disabled)
> +		return NULL;

Not much I can restore here..

Is is_migration_disabled(p) be more correct to check migration disable.
And get_push_task() being called in pull_rt_task() has checked migration
disable first and then call get_push_task(). That means this check in
get_push_task() in patch is a second repeatly check.

>  	rq->push_busy = true;
>  	return get_task_struct(p);
>  }
> -- 
> 2.33.0
> 



Thanks,
Tao

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] sched: Fix get_push_task() vs migrate_disable()
  2021-08-26 13:37 [PATCH] sched: Fix get_push_task() vs migrate_disable() Sebastian Andrzej Siewior
  2021-08-26 16:24 ` Tao Zhou
@ 2021-08-26 16:56 ` Peter Zijlstra
  2021-08-26 17:07 ` [tip: sched/urgent] " tip-bot2 for Sebastian Andrzej Siewior
  2 siblings, 0 replies; 6+ messages in thread
From: Peter Zijlstra @ 2021-08-26 16:56 UTC (permalink / raw)
  To: Sebastian Andrzej Siewior
  Cc: linux-kernel, Ingo Molnar, Juri Lelli, Vincent Guittot,
	Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	Daniel Bristot de Oliveira, Thomas Gleixner

On Thu, Aug 26, 2021 at 03:37:38PM +0200, Sebastian Andrzej Siewior wrote:
> push_rt_task() attempts to move the currently running task away if the
> next runnable task has migration disabled and therefore is pinned on the
> current CPU.
> 
> The current task is retrieved via get_push_task() which only checks for
> nr_cpus_allowed == 1, but does not check whether the task has migration
> disabled and therefore cannot be moved either. The consequence is a
> pointless invocation of the migration thread which correctly observes
> that the task cannot be moved.
> 
> Return NULL if the task has migration disabled and cannot be moved to
> another CPU.
> 
> Fixes: a7c81556ec4d3 ("sched: Fix migrate_disable() vs rt/dl balancing")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Thanks!

^ permalink raw reply	[flat|nested] 6+ messages in thread

* [tip: sched/urgent] sched: Fix get_push_task() vs migrate_disable()
  2021-08-26 13:37 [PATCH] sched: Fix get_push_task() vs migrate_disable() Sebastian Andrzej Siewior
  2021-08-26 16:24 ` Tao Zhou
  2021-08-26 16:56 ` Peter Zijlstra
@ 2021-08-26 17:07 ` tip-bot2 for Sebastian Andrzej Siewior
  2 siblings, 0 replies; 6+ messages in thread
From: tip-bot2 for Sebastian Andrzej Siewior @ 2021-08-26 17:07 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Sebastian Andrzej Siewior, Peter Zijlstra (Intel), x86, linux-kernel

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     e681dcbaa4b284454fecd09617f8b24231448446
Gitweb:        https://git.kernel.org/tip/e681dcbaa4b284454fecd09617f8b24231448446
Author:        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate:    Thu, 26 Aug 2021 15:37:38 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 26 Aug 2021 19:02:00 +02:00

sched: Fix get_push_task() vs migrate_disable()

push_rt_task() attempts to move the currently running task away if the
next runnable task has migration disabled and therefore is pinned on the
current CPU.

The current task is retrieved via get_push_task() which only checks for
nr_cpus_allowed == 1, but does not check whether the task has migration
disabled and therefore cannot be moved either. The consequence is a
pointless invocation of the migration thread which correctly observes
that the task cannot be moved.

Return NULL if the task has migration disabled and cannot be moved to
another CPU.

Fixes: a7c81556ec4d3 ("sched: Fix migrate_disable() vs rt/dl balancing")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210826133738.yiotqbtdaxzjsnfj@linutronix.de
---
 kernel/sched/sched.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index da4295f..ddefb04 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2255,6 +2255,9 @@ static inline struct task_struct *get_push_task(struct rq *rq)
 	if (p->nr_cpus_allowed == 1)
 		return NULL;
 
+	if (p->migration_disabled)
+		return NULL;
+
 	rq->push_busy = true;
 	return get_task_struct(p);
 }

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] sched: Fix get_push_task() vs migrate_disable()
  2021-08-26 16:24 ` Tao Zhou
@ 2021-08-26 19:38   ` Thomas Gleixner
  2021-08-26 22:53     ` Tao Zhou
  0 siblings, 1 reply; 6+ messages in thread
From: Thomas Gleixner @ 2021-08-26 19:38 UTC (permalink / raw)
  To: Tao Zhou, Sebastian Andrzej Siewior, linux-kernel, tao.zhou
  Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
	Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	Daniel Bristot de Oliveira

Tao,

On Fri, Aug 27 2021 at 00:24, Tao Zhou wrote:
> On Thu, Aug 26, 2021 at 03:37:38PM +0200, Sebastian Andrzej Siewior wrote:
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index e205b63d6db07..32a4945730a9b 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -2259,6 +2259,9 @@ static inline struct task_struct *get_push_task(struct rq *rq)
>>  	if (p->nr_cpus_allowed == 1)
>>  		return NULL;
>>  
>> +	if (p->migration_disabled)
>> +		return NULL;
>
> Not much I can restore here..
>
> Is is_migration_disabled(p) be more correct to check migration
> disable.

Kinda, but it's not an issue here because get_push_task() is only available when
CONFIG_SMP=y which makes p->migration_disabled available as well.

> And get_push_task() being called in pull_rt_task() has checked migration
> disable first and then call get_push_task(). That means this check in
> get_push_task() in patch is a second repeatly check.

No. The checks are for two different tasks...

Thanks,

        tglx

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] sched: Fix get_push_task() vs migrate_disable()
  2021-08-26 19:38   ` Thomas Gleixner
@ 2021-08-26 22:53     ` Tao Zhou
  0 siblings, 0 replies; 6+ messages in thread
From: Tao Zhou @ 2021-08-26 22:53 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: Sebastian Andrzej Siewior, Ingo Molnar, Peter Zijlstra,
	Juri Lelli, Vincent Guittot, Dietmar Eggemann, Steven Rostedt,
	Ben Segall, Mel Gorman, Daniel Bristot de Oliveira, linux-kernel,
	tao.zhou

Hi Thomas,

On Thu, Aug 26, 2021 at 09:38:17PM +0200, Thomas Gleixner wrote:
> Tao,
> 
> On Fri, Aug 27 2021 at 00:24, Tao Zhou wrote:
> > On Thu, Aug 26, 2021 at 03:37:38PM +0200, Sebastian Andrzej Siewior wrote:
> >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> >> index e205b63d6db07..32a4945730a9b 100644
> >> --- a/kernel/sched/sched.h
> >> +++ b/kernel/sched/sched.h
> >> @@ -2259,6 +2259,9 @@ static inline struct task_struct *get_push_task(struct rq *rq)
> >>  	if (p->nr_cpus_allowed == 1)
> >>  		return NULL;
> >>  
> >> +	if (p->migration_disabled)
> >> +		return NULL;
> >
> > Not much I can restore here..
> >
> > Is is_migration_disabled(p) be more correct to check migration
> > disable.
> 
> Kinda, but it's not an issue here because get_push_task() is only available when
> CONFIG_SMP=y which makes p->migration_disabled available as well.
> 
> > And get_push_task() being called in pull_rt_task() has checked migration
> > disable first and then call get_push_task(). That means this check in
> > get_push_task() in patch is a second repeatly check.
> 
> No. The checks are for two different tasks...

Aha, yes. I lost here. Thanks for your reply.

> Thanks,
> 
>         tglx



Thanks,
Tao

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2021-08-26 22:53 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-08-26 13:37 [PATCH] sched: Fix get_push_task() vs migrate_disable() Sebastian Andrzej Siewior
2021-08-26 16:24 ` Tao Zhou
2021-08-26 19:38   ` Thomas Gleixner
2021-08-26 22:53     ` Tao Zhou
2021-08-26 16:56 ` Peter Zijlstra
2021-08-26 17:07 ` [tip: sched/urgent] " tip-bot2 for Sebastian Andrzej Siewior

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