Re: [RFC 05/13] x86/mm: Add barriers and document switch_mm-vs-flush synchronization

[Nadav Amit]

Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:

> On Fri, Jun 3, 2016 at 10:42 AM, Nadav Amit <nadav.amit@xxxxxxxxx> wrote:
>> Following this patch, if (current->active_mm != mm), flush_tlb_page() still
>> doesnât call smp_mb() before checking mm_cpumask(mm).
>> 
>> In contrast, flush_tlb_mm_range() does call smp_mb().
>> 
>> Is there a reason for this discrepancy?
> 
> Not that I can remember.  Is the remote flush case likely to be racy?

You replied separately on another email that included a patch to fix
this case. It turns out smp_mb is not needed on flush_tlb_page, since
the PTE is always updated using an atomic operation. Yet, a compiler 
barrier is still needed, so I added smp_mb__after_atomic instead.

Nadav