linux-kernel - Re: [PATCH v5 3/3] mm/khugepaged: maintain page cache uptodate flag

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Message-ID: <CAPhsuW5pTh2+S7VjRbRy=WUAb7-GLQpi6HKCW0ehxs5HAup_dQ@mail.gmail.com>
Date:   Thu, 23 Mar 2023 15:28:22 -0700
From:   Song Liu <song@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Hugh Dickins <hughd@...gle.com>, Song Liu <songliubraving@...com>,
        Jiri Olsa <jolsa@...nel.org>,
        David Stevens <stevensd@...omium.org>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Yang Shi <shy828301@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Jiaqi Yan <jiaqiyan@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] mm/khugepaged: maintain page cache uptodate flag

On Thu, Mar 23, 2023 at 2:56 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Thu, Mar 23, 2023 at 12:07:46PM -0700, Hugh Dickins wrote:
> > On an earlier audit, for different reasons, I did also run across
> > lib/buildid.c build_id_parse() using find_get_page() without checking
> > PageUptodate() - looks as if it might do the wrong thing if it races
> > with khugepaged collapsing text to huge, and should probably have a
> > similar fix.
>
> That shouldn't be using find_get_page().  It should probably use
> read_cache_folio() which will actually read in the data if it's not
> present in the page cache, and return an ERR_PTR if the data couldn't
> be read.

build_id_parse() can be called from NMI, so I don't think we can let
read_cache_folio() read-in the data.

Thanks,
Song