linux-kernel - Re: [v5 PATCH 6/6] mm: hwpoison: handle non-anonymous THP correctly

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Message-ID: <YYC1Phb5eFn9hJfG@casper.infradead.org>
Date:   Tue, 2 Nov 2021 03:49:18 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Yang Shi <shy828301@...il.com>
Cc:     Jue Wang <juew@...gle.com>, Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>, Oscar Salvador <osalvador@...e.de>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [v5 PATCH 6/6] mm: hwpoison: handle non-anonymous THP correctly

On Mon, Nov 01, 2021 at 01:11:33PM -0700, Yang Shi wrote:
> On Mon, Nov 1, 2021 at 12:38 PM Jue Wang <juew@...gle.com> wrote:
> >
> > A related bug but whose fix may belong to a separate series:
> >
> > split_huge_page fails when invoked concurrently on the same THP page.
> >
> > It's possible that multiple memory errors on the same THP get consumed
> > by multiple threads and come down to split_huge_page path easily.
> 
> Yeah, I think it should be a known problem since the very beginning.
> The THP split requires to pin the page and does check if the refcount
> is expected or not and freezes the refcount if it is expected. So if
> two concurrent paths try to split the same THP, one will fail due to
> the pin from the other path, but the other one will succeed.

No, they can both fail, if the timing is just right, because they each
have a refcount, so neither will succeed.