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From:   Yang Shi <shy828301@gmail.com>
Date:   Mon, 20 Sep 2021 14:23:41 -0700
Message-ID: <CAHbLzkrPDDoOsPXQD3Y3Kbmex4ptYH+Ad_P1Ds_ateWb+65Rng@mail.gmail.com>
Subject: Re: [PATCH] fs: buffer: check huge page size instead of single page
 for invalidatepage
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Hugh Dickins <hughd@google.com>, cfijalkovich@google.com,
        song@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
        Hao Sun <sunhao.th@gmail.com>, Linux MM <linux-mm@kvack.org>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Song Liu <songliubraving@fb.com>
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On Sun, Sep 19, 2021 at 7:41 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Fri, Sep 17, 2021 at 05:07:03PM -0700, Yang Shi wrote:
> > > The debugging showed the page passed to invalidatepage is a huge page
> > > and the length is the size of huge page instead of single page due to
> > > read only FS THP support.  But block_invalidatepage() would throw BUG if
> > > the size is greater than single page.
>
> Things have already gone wrong before we get to this point.  See
> do_dentry_open().  You aren't supposed to be able to get a writable file
> descriptor on a file which has had huge pages added to the page cache
> without the filesystem's knowledge.  That's the problem that needs to
> be fixed.

I don't quite understand your point here. Do you mean do_dentry_open()
should fail for such cases instead of truncating the page cache?