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Date:   Sun, 19 Sep 2021 15:40:30 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Yang Shi <shy828301@gmail.com>
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>
Subject: Re: [PATCH] fs: buffer: check huge page size instead of single page
 for invalidatepage
Message-ID: <YUdL3lFLFHzC80Wt@casper.infradead.org>
References: <20210917205731.262693-1-shy828301@gmail.com>
 <CAHbLzkqmooOJ0A6JmGD+y5w_BcFtSAJtKBXpXxYNcYrzbpCrNQ@mail.gmail.com>
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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.