linux-kernel - Re: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy (was: Re: [RESEND PATCH] mm, oom_reaper: gather each vma to prevent) leaking TLB entry

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Message-ID: <20171116004457.GA12222@bbox>
Date:   Thu, 16 Nov 2017 09:44:57 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Wang Nan <wangnan0@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, will.deacon@....com,
        Bob Liu <liubo95@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, Roman Gushchin <guro@...com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy (was: Re:
 [RESEND PATCH] mm, oom_reaper: gather each vma to prevent) leaking TLB entry

On Wed, Nov 15, 2017 at 09:14:52AM +0100, Michal Hocko wrote:
> On Mon 13-11-17 09:28:33, Minchan Kim wrote:
> [...]
> > void arch_tlb_gather_mmu(...)
> > 
> >         tlb->fullmm = !(start | (end + 1)) && atomic_read(&mm->mm_users) == 0;
> 
> Sorry, I should have realized sooner but this will not work for the oom
> reaper. It _can_ race with the final exit_mmap and run with mm_users == 0

If someone see mm_users is zero, it means there is no user to access
address space by stale TLB. Am I missing something?