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SubjectRe: [PATCH 1/2] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable()
On Tue, Oct 13, 2020 at 04:15:08PM +0200, Sebastian Andrzej Siewior wrote:
> On 2020-10-13 15:01:15 [+0100], Valentin Schneider wrote:
> > migrate_disable();
> > set_cpus_allowed_ptr(current, {something excluding task_cpu(current)});
> > affine_move_task(); <-- never returns
> >
> > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> > ---
> > kernel/sched/core.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 4ccd1099adaa..7f4e38819de1 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -2189,6 +2189,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
> > if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, new_mask))
> > goto out;
> >
> > + if (p == current &&
> > + is_migration_disabled(p) &&
> > + !cpumask_test_cpu(task_cpu(p), new_mask))
> > + ret = -EBUSY;
> > +
>
> This shouldn't happen, right? The function may sleep so it shouldn't be
> entered with disabled migration. A WARN_ON might spot the bad caller.

So yeah, I like detecting the case but agree with bigeasy that an
additional WARN would make sense, lemme go add that.

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