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Date:   Fri, 18 Feb 2022 08:51:54 +0100
From:   Greg Kroah-Hartman <>
To:     Theodore Ts'o <>
Cc:     John Hubbard <>,
        Lee Jones <>,,
        Christoph Hellwig <>,
        Dave Chinner <>,
        Goldwyn Rodrigues <>,
        "Darrick J . Wong" <>,
        Bob Peterson <>,
        Damien Le Moal <>,
        Andreas Gruenbacher <>,
        Ritesh Harjani <>,
        Johannes Thumshirn <>,,,,
Subject: Re: [REPORT] kernel BUG at fs/ext4/inode.c:2620 - page_buffers()

On Thu, Feb 17, 2022 at 11:08:38PM -0500, Theodore Ts'o wrote:
> On Thu, Feb 17, 2022 at 05:06:45PM -0800, John Hubbard wrote:
> > Yes. And looking at the pair of backtraces below, this looks very much
> > like another aspect of the "get_user_pages problem" [1], originally
> > described in Jan Kara's 2018 email [2].
> Hmm... I just posted my analysis, which tracks with yours; but I had
> forgotten about Jan's 2018 e-mail on the matter.
> > I'm getting close to posting an RFC for the direct IO conversion to
> > FOLL_PIN, but even after that, various parts of the kernel (reclaim,
> > filesystems/block layer) still need to be changed so as to use
> > page_maybe_dma_pinned() to help avoid this problem. There's a bit
> > more than that, actually.
> The challenge is that fixing this "the right away" is probably not
> something we can backport into an LTS kernel, whether it's 5.15 or
> 5.10... or 4.19.

Don't worry about stable backports to start with.  Do it the "right way"
first and then we can consider if it needs to be backported or not.


greg k-h

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