linux-ext4 - Re: [PATCH 8/9] btrfs: handle a NULL folio in extent_range_redirty_for

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Date:   Wed, 18 Jan 2023 17:42:47 +0100
From:   Christoph Hellwig <hch@....de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, linux-afs@...ts.infradead.org,
        linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        cluster-devel@...hat.com, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-nilfs@...r.kernel.org
Subject: Re: [PATCH 8/9] btrfs: handle a NULL folio in
 extent_range_redirty_for_io

On Wed, Jan 18, 2023 at 04:08:57PM +0000, Matthew Wilcox wrote:
> On Wed, Jan 18, 2023 at 10:43:28AM +0100, Christoph Hellwig wrote:
> > filemap_get_folio can return NULL, skip those cases.
> 
> Hmm, I'm not sure that's true.  We have one place that calls
> extent_range_redirty_for_io(), and it previously calls
> extent_range_clear_dirty_for_io() which has an explicit
> 
>                 BUG_ON(!page); /* Pages should be in the extent_io_tree */
> 
> so I'm going to say this one can't happen either.  I haven't delved far
> enough into btrfs to figure out why it can't happen.

I'll drop this patch for now.