[PATCH] sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr

[PATCH] sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr

[Sebastian Andrzej Siewior]

From: Scott Wood <swood@redhat.com>

This function is concerned with the long-term cpu mask, not the
transitory mask the task might have while migrate disabled.  Before
this patch, if a task was migrate disabled at the time
__set_cpus_allowed_ptr() was called, and the new mask happened to be
equal to the cpu that the task was running on, then the mask update
would be lost.

Signed-off-by: Scott Wood <swood@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/sched/core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1637,7 +1637,7 @@ static int __set_cpus_allowed_ptr(struct
 		goto out;
 	}
 
-	if (cpumask_equal(p->cpus_ptr, new_mask))
+	if (cpumask_equal(&p->cpus_mask, new_mask))
 		goto out;
 
 	/*

Re: [PATCH] sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr

[Valentin Schneider]

On 17/06/20 13:17, Sebastian Andrzej Siewior wrote:
> From: Scott Wood <swood@redhat.com>
>
> This function is concerned with the long-term cpu mask, not the
> transitory mask the task might have while migrate disabled.  Before
> this patch, if a task was migrate disabled at the time
> __set_cpus_allowed_ptr() was called, and the new mask happened to be
> equal to the cpu that the task was running on, then the mask update
> would be lost.
>
> Signed-off-by: Scott Wood <swood@redhat.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  kernel/sched/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1637,7 +1637,7 @@ static int __set_cpus_allowed_ptr(struct
>               goto out;
>       }
>
> -	if (cpumask_equal(p->cpus_ptr, new_mask))
> +	if (cpumask_equal(&p->cpus_mask, new_mask))
>               goto out;
>
>       /*

Makes sense, but what about the rest of the checks? Further down there is

        /* Can the task run on the task's current CPU? If so, we're done */
        if (cpumask_test_cpu(task_cpu(p), new_mask))
                goto out;

If the task is currently migrate disabled and for some stupid reason it
gets affined elsewhere, we could try to move it out - which AFAICT we don't
want to do because migrate disabled. So I suppose you'd want an extra
bailout condition here when the task is migrate disabled.

ISTR in RT you do re-check the affinity and potentially move the task away
when re-enabling migration, so that should work out all fine.

Re: [PATCH] sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr

[Scott Wood]

On Wed, 2020-06-17 at 15:15 +0100, Valentin Schneider wrote:
> On 17/06/20 13:17, Sebastian Andrzej Siewior wrote:
> > From: Scott Wood <swood@redhat.com>
> > 
> > This function is concerned with the long-term cpu mask, not the
> > transitory mask the task might have while migrate disabled.  Before
> > this patch, if a task was migrate disabled at the time
> > __set_cpus_allowed_ptr() was called, and the new mask happened to be
> > equal to the cpu that the task was running on, then the mask update
> > would be lost.
> > 
> > Signed-off-by: Scott Wood <swood@redhat.com>
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> >  kernel/sched/core.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1637,7 +1637,7 @@ static int __set_cpus_allowed_ptr(struct
> >               goto out;
> >       }
> > 
> > -	if (cpumask_equal(p->cpus_ptr, new_mask))
> > +	if (cpumask_equal(&p->cpus_mask, new_mask))
> >               goto out;
> > 
> >       /*
> 
> Makes sense, but what about the rest of the checks? Further down there is
> 
>         /* Can the task run on the task's current CPU? If so, we're done
> */
>         if (cpumask_test_cpu(task_cpu(p), new_mask))
>                 goto out;
> 
> If the task is currently migrate disabled and for some stupid reason it
> gets affined elsewhere, we could try to move it out - which AFAICT we
> don't
> want to do because migrate disabled. So I suppose you'd want an extra
> bailout condition here when the task is migrate disabled.
> 
> ISTR in RT you do re-check the affinity and potentially move the task away
> when re-enabling migration, so that should work out all fine.

On RT the above test is:

        /* Can the task run on the task's current CPU? If so, we're done */
        if (cpumask_test_cpu(task_cpu(p), new_mask) ||
            p->cpus_ptr != &p->cpus_mask)
                goto out;

...so we do bail out if we're migrate disabled.

-Scott

Re: [PATCH] sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr

[Sebastian Andrzej Siewior]

On 2020-06-17 17:49:48 [-0500], Scott Wood wrote:
> > Makes sense, but what about the rest of the checks? Further down there is
> > 
> >         /* Can the task run on the task's current CPU? If so, we're done
> > */
> >         if (cpumask_test_cpu(task_cpu(p), new_mask))
> >                 goto out;
> > 
> > If the task is currently migrate disabled and for some stupid reason it
> > gets affined elsewhere, we could try to move it out - which AFAICT we
> > don't
> > want to do because migrate disabled. So I suppose you'd want an extra
> > bailout condition here when the task is migrate disabled.
> > 
> > ISTR in RT you do re-check the affinity and potentially move the task away
> > when re-enabling migration, so that should work out all fine.
> 
> On RT the above test is:
> 
>         /* Can the task run on the task's current CPU? If so, we're done */
>         if (cpumask_test_cpu(task_cpu(p), new_mask) ||
>             p->cpus_ptr != &p->cpus_mask)
>                 goto out;
> 
> ...so we do bail out if we're migrate disabled.

correct. There is a complete migrate_disable() patch in the RT queue
which has to wait. This patch however looked to be independent of that
and could "fix" the pointer part which is already here so I sent it.

> -Scott

Sebastian

Re: [PATCH] sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr

[Valentin Schneider]

On 18/06/20 09:07, Sebastian Andrzej Siewior wrote:
> On 2020-06-17 17:49:48 [-0500], Scott Wood wrote:
>> > Makes sense, but what about the rest of the checks? Further down there is
>> >
>> >         /* Can the task run on the task's current CPU? If so, we're done
>> > */
>> >         if (cpumask_test_cpu(task_cpu(p), new_mask))
>> >                 goto out;
>> >
>> > If the task is currently migrate disabled and for some stupid reason it
>> > gets affined elsewhere, we could try to move it out - which AFAICT we
>> > don't
>> > want to do because migrate disabled. So I suppose you'd want an extra
>> > bailout condition here when the task is migrate disabled.
>> >
>> > ISTR in RT you do re-check the affinity and potentially move the task away
>> > when re-enabling migration, so that should work out all fine.
>>
>> On RT the above test is:
>>
>>         /* Can the task run on the task's current CPU? If so, we're done */
>>         if (cpumask_test_cpu(task_cpu(p), new_mask) ||
>>             p->cpus_ptr != &p->cpus_mask)
>>                 goto out;
>>
>> ...so we do bail out if we're migrate disabled.
>
> correct. There is a complete migrate_disable() patch in the RT queue
> which has to wait. This patch however looked to be independent of that
> and could "fix" the pointer part which is already here so I sent it.
>

Okay, thanks. I don't see any harm in including that extra check with the
patch, but either way:

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

>> -Scott
>
> Sebastian

[tip: sched/urgent] sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr

[tip-bot2 for Scott Wood]

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

Commit-ID:     a51dde512a93959d1df3a915fa3e3df68b1fc94d
Gitweb:        https://git.kernel.org/tip/a51dde512a93959d1df3a915fa3e3df68b1fc94d
Author:        Scott Wood <swood@redhat.com>
AuthorDate:    Wed, 17 Jun 2020 14:17:42 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 22 Jun 2020 20:51:05 +02:00

sched: __set_cpus_allowed_ptr(): Check cpus_mask, not cpus_ptr

This function is concerned with the long-term cpu mask, not the
transitory mask the task might have while migrate disabled.  Before
this patch, if a task was migrate disabled at the time
__set_cpus_allowed_ptr() was called, and the new mask happened to be
equal to the cpu that the task was running on, then the mask update
would be lost.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Scott Wood <swood@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200617121742.cpxppyi7twxmpin7@linutronix.de
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8298b2c..9f8aa34 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1637,7 +1637,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 		goto out;
 	}
 
-	if (cpumask_equal(p->cpus_ptr, new_mask))
+	if (cpumask_equal(&p->cpus_mask, new_mask))
 		goto out;
 
 	/*

[tip: sched/urgent] sched/core: Check cpus_mask, not cpus_ptr in __set_cpus_allowed_ptr(), to fix mask corruption

[tip-bot2 for Scott Wood]

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

Commit-ID:     16568f1f4fd4decee6935751d5ada1f963e5bd5f
Gitweb:        https://git.kernel.org/tip/16568f1f4fd4decee6935751d5ada1f963e5bd5f
Author:        Scott Wood <swood@redhat.com>
AuthorDate:    Wed, 17 Jun 2020 14:17:42 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 23 Jun 2020 10:42:30 +02:00

sched/core: Check cpus_mask, not cpus_ptr in __set_cpus_allowed_ptr(), to fix mask corruption

This function is concerned with the long-term CPU mask, not the
transitory mask the task might have while migrate disabled.  Before
this patch, if a task was migrate-disabled at the time
__set_cpus_allowed_ptr() was called, and the new mask happened to be
equal to the CPU that the task was running on, then the mask update
would be lost.

Signed-off-by: Scott Wood <swood@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200617121742.cpxppyi7twxmpin7@linutronix.de
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8f36032..9eeac94 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1637,7 +1637,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
 		goto out;
 	}
 
-	if (cpumask_equal(p->cpus_ptr, new_mask))
+	if (cpumask_equal(&p->cpus_mask, new_mask))
 		goto out;
 
 	/*