Re: [PATCH] sched/core: Fix a missed update of user_cpus_ptr

[Waiman Long]

On 2/3/23 16:04, Tejun Heo wrote:
> On Fri, Feb 03, 2023 at 01:18:49PM -0500, Waiman Long wrote:
> > Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested
> > cpumask"), a successful call to sched_setaffinity() should always save
> > the user requested cpu affinity mask in a task's user_cpus_ptr. However,
> > when the given cpu mask is the same as the current one, user_cpus_ptr
> > is not updated. Fix this by saving the user mask in this case too.
> >
> > Fixes: 8f9ea86fdf99 ("sched: Always preserve the user requested cpumask")
> > Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> > ---
> >   kernel/sched/core.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 30d9752e2ca5..91255f791df3 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -2951,8 +2951,11 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
> >   	}
> >   
> >   	if (!(ctx->flags & SCA_MIGRATE_ENABLE)) {
> > -		if (cpumask_equal(&p->cpus_mask, ctx->new_mask))
> > +		if (cpumask_equal(&p->cpus_mask, ctx->new_mask)) {
> > +			if (ctx->flags & SCA_USER)
> > +				swap(p->user_cpus_ptr, ctx->user_mask);
> >   			goto out;
> > +		}
> >   
> >   		if (WARN_ON_ONCE(p == current &&
> >   				 is_migration_disabled(p) &&
> and this is for a separate bug and should go through the scheduler tree.

Yes, this is for Peter to pick up.

Cheers,
Longman