linux-kernel - Re: [PATCH] mm, numa: fix bad pmd by atomically check for pmd_trans_huge when marking page tables prot

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Message-Id: <917137D2-FD66-4175-AC69-23F8206186C5@lca.pw>
Date:   Tue, 10 Mar 2020 20:04:11 -0400
From:   Qian Cai <cai@....pw>
To:     Rafael Aquini <aquini@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        mgorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm, numa: fix bad pmd by atomically check for
 pmd_trans_huge when marking page tables prot_numa



> On Mar 9, 2020, at 11:05 AM, Rafael Aquini <aquini@...hat.com> wrote:
> I'm still waiting on a similar system to become available, so I can
> work on your reproducer case, as well as to dig and wrap my head around it.
> 
> I still don't think that skipping the pmd_none() in the change-protection walk 
> should cause a big fuss like you observed here (yet, it seems it does), and 
> the fact that we need that race window to take the __split_huge_pmd() suggests,
> at least to me, that we might be missing this proper split somewhere else.

I have sent out another patch which should be more correct,

https://lore.kernel.org/lkml/20200310235846.1319-1-cai@lca.pw/