linux-ext4 - Re: [PATCH 07/15] fsverity: don't issue readahead for non-ENOENT errors from __filemap_get

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Message-ID: <20260128234814.GC2024@quark>
Date: Wed, 28 Jan 2026 15:48:14 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Al Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	David Sterba <dsterba@...e.com>, Theodore Ts'o <tytso@....edu>,
	Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
	Andrey Albershteyn <aalbersh@...hat.com>,
	Matthew Wilcox <willy@...radead.org>, linux-fsdevel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net, fsverity@...ts.linux.dev
Subject: Re: [PATCH 07/15] fsverity: don't issue readahead for non-ENOENT
 errors from __filemap_get_folio

On Wed, Jan 28, 2026 at 04:26:19PM +0100, Christoph Hellwig wrote:
> Issuing more reads on errors is not a good idea, especially when the
> most common error here is -ENOMEM.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  fs/verity/pagecache.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/verity/pagecache.c b/fs/verity/pagecache.c
> index f67248e9e768..eae419d8d091 100644
> --- a/fs/verity/pagecache.c
> +++ b/fs/verity/pagecache.c
> @@ -22,7 +22,8 @@ struct page *generic_read_merkle_tree_page(struct inode *inode, pgoff_t index,
>  	struct folio *folio;
>  
>  	folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
> -	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
> +	if (folio == ERR_PTR(-ENOENT) ||
> +	    (!IS_ERR(folio) && !folio_test_uptodate(folio))) {
>  		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);

This patch is still incorrect: when IS_ERR(folio) && folio !=
ERR_PTR(-ENOENT) it falls through to folio_file_page(), which crashes.
See https://lore.kernel.org/r/20260126205301.GD30838@quark/ for a
correct suggestion.

- Eric