Re: linux-next: manual merge of the rcu tree with the tip tree

[Andy Lutomirski]

On Tue, Aug 1, 2017 at 7:15 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Tue, Aug 01, 2017 at 03:58:49PM +0200, Peter Zijlstra wrote:
>> On Tue, Aug 01, 2017 at 06:43:14AM -0700, Andy Lutomirski wrote:
>> > Anyway, can you document whatever property you require with a comment
>> > in switch_mm() or wherever you're finding that property so that future
>> > arch changes don't break it?
>>
>> We need _a_ smp_mb after rq->curr store. x86 has plenty.
>
> That is, we need it when we change to a different !0 mm. And we have the
> mm_cpumask() atomics at the very least, even if loading a new CR3 would
> not be serializing.

I'm 99.5% sure that loading a new CR3 is always serializing even if it
doesn't flush the TLB.