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

From	Nadav Amit <nadav.amit@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [RFC 05/13] x86/mm: Add barriers and document switch_mm-vs-flush synchronization
Date	2016-06-09 21:50 +0200
Message-ID	<rIe7L-2nM-13@gated-at.bofh.it> (permalink)
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Andy Lutomirski <luto@amacapital.net> wrote:

> On Fri, Jun 3, 2016 at 10:42 AM, Nadav Amit <nadav.amit@gmail.com> wrote:
>> Following this patch, if (current->active_mm != mm), flush_tlb_page() still
>> doesn’t 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

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Re: [RFC 05/13] x86/mm: Add barriers and document switch_mm-vs-flush synchronization Nadav Amit <nadav.amit@gmail.com> - 2016-06-03 19:50 +0200
  Re: [RFC 05/13] x86/mm: Add barriers and document switch_mm-vs-flush synchronization Andy Lutomirski <luto@amacapital.net> - 2016-06-09 19:30 +0200
    Re: [RFC 05/13] x86/mm: Add barriers and document switch_mm-vs-flush synchronization Nadav Amit <nadav.amit@gmail.com> - 2016-06-09 21:50 +0200

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