Re: mm: deadlock between get_online_cpus/pcpu_alloc

[Peter Zijlstra]

On Wed, Feb 08, 2017 at 02:03:32PM +0000, Mel Gorman wrote:
> > Yeah, we'll sort that out once it hits Linus tree and we move RT forward.
> > Though I have once complaint right away:
> > 
> > +	preempt_enable_no_resched();
> > 
> > This is a nono, even in mainline. You effectively disable a preemption
> > point.
> > 
> 
> This came up during review on whether it should or shouldn't be a preemption
> point. Initially it was preempt_enable() but a preemption point didn't
> exist before, the reviewer pushed for it and as it was the allocator fast
> path that was unlikely to need a reschedule or preempt, I made the change.

Not relevant. The only acceptable use of preempt_enable_no_resched() is
if the next statement is a schedule() variant.