Re: softlockups in multi_cpu_stop

Davidlohr Bueso
2015-03-06T22:15:49Z

On Fri, 2015-03-06 at 13:12 -0800, Jason Low wrote:
> In owner_running() there are 2 conditions that would make it return
> false: if the owner changed or if the owner is not running. However,
> that patch continues spinning if there is a "new owner" but it does not
> take into account that we may want to stop spinning if the owner is not
> running (due to getting rescheduled).

So you're rationale is that we're missing this need_resched:

while (owner_running(sem, owner)) {
/* abort spinning when need_resched */
if (need_resched()) {
rcu_read_unlock();
return false;
}
}

Because the owner_running() would return false, right? Yeah that makes
sense, as missing a resched is a bug, as opposed to our heuristics being
so painfully off.

Sasha, Ming (Cc'ed), does this address the issues you guys are seeing?

Thanks,
Davidlohr