Andy Lutomirski [off-list ref] wrote:

On Fri, Jun 3, 2016 at 10:42 AM, Nadav Amit [off-list ref] wrote:

quoted

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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