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Date:   Tue, 2 Nov 2021 03:49:18 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Yang Shi <shy828301@gmail.com>
Cc:     Jue Wang <juew@google.com>, Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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        <naoya.horiguchi@nec.com>, Oscar Salvador <osalvador@suse.de>,
        Peter Xu <peterx@redhat.com>
Subject: Re: [v5 PATCH 6/6] mm: hwpoison: handle non-anonymous THP correctly
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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@google.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.