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 16:08:57 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@....de>
Cc:     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 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.

> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  fs/btrfs/extent_io.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index d55e4531ffd212..a54d2cf74ba020 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -230,6 +230,8 @@ void extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end)
>  
>  	while (index <= end_index) {
>  		folio = filemap_get_folio(mapping, index);
> +		if (!folio)
> +			continue;
>  		filemap_dirty_folio(mapping, folio);
>  		folio_account_redirty(folio);
>  		index += folio_nr_pages(folio);
> -- 
> 2.39.0
>