On 24/09/20 13:29, Peter Zijlstra wrote:
> On Thu, Sep 24, 2020 at 12:53:25PM +0100, Valentin Schneider wrote:
>> On 21/09/20 17:36, Peter Zijlstra wrote:
>>
>> [...]
>>
>> > +void migrate_enable(void)
>> > +{
>> > + if (--current->migration_disabled)
>> > + return;
>> > +
>> > + barrier();
>> > +
>> > + if (p->cpus_ptr == &p->cpus_mask)
>> > + return;
>>
>> If we get to here this means we're the migrate_enable() invocation that
>> marks the end of the migration_disabled region. How can cpus_ptr already
>> point back to current's cpus_mask?
>
> It might never have been changed away.
>
>
> migrate_disable()
> ->migration_disabled++;
> | |
> | |
> | v
> | migrate_disable_switch()
> | if (->cpus_ptr == &->cpus_mask)
> | __do_set_cpus_allowed(.new_mask = cpumask_of())
> | |
> | |
> v v
> migrate_enable()
> ->migration_disabled--;
>
>
> Only if we've passed through a context switch between migrate_disable()
> and migrate_enable() will the mask have been changed.
Doh, yes indeed. Thanks.
