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 <sw...@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 <sw...@redhat.com> > > Signed-off-by: Sebastian Andrzej Siewior <bige...@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