Re: [PATCH RT] sched/migrate_disable: fallback to preempt_disable() instead barrier()

From: Sebastian Andrzej Siewior
Date: Thu Jul 05 2018 - 12:59:52 EST

On 2018-07-05 12:18:07 [-0400], joe.korty@xxxxxxxxxxxxxxxxx wrote:
> Hi Sebastian,
Hi Joe,

> I just verified that this fix does not work for my mix of
> config options (smp && preempt && !rt).

Okay. So for !RT+SMP we keep migrate_disable() around and it almost
nothing. And it is not referenced anywhere so it does not matter as long
as it not used directly.

We could turn migrate_disable() into a nop/barrier but then we have
three uses which do preempt_disable() -> migrate_disable() (see other
For the futex code it should not matter much because at this point
preemption is disabled due to the spin_lock() (so we would just extend
it past the spin_unlock() or wake_futex_pi() which ends with

> Regards,
> Joe