linux-kernel - Re: [PATCH] fs: buffer: check huge page size instead of single page for invalidatepage

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Date:   Mon, 20 Sep 2021 14:23:41 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Hugh Dickins <hughd@...gle.com>, cfijalkovich@...gle.com,
        song@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
        Hao Sun <sunhao.th@...il.com>, Linux MM <linux-mm@...ck.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Song Liu <songliubraving@...com>
Subject: Re: [PATCH] fs: buffer: check huge page size instead of single page
 for invalidatepage

On Sun, Sep 19, 2021 at 7:41 AM Matthew Wilcox <willy@...radead.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?