linux-kernel - Re: [PATCH 01/14] writeback: don't call mapping_set_error on AOP_WRITEPAGE

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Message-ID: <Zc35HOF8+vVEkdQu@bfoster>
Date: Thu, 15 Feb 2024 06:44:28 -0500
From: Brian Foster <bfoster@...hat.com>
To: Christoph Hellwig <hch@....de>
Cc: linux-mm@...ck.org, Matthew Wilcox <willy@...radead.org>,
	Jan Kara <jack@...e.com>, David Howells <dhowells@...hat.com>,
	Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/14] writeback: don't call mapping_set_error on
 AOP_WRITEPAGE_ACTIVATE

On Thu, Feb 15, 2024 at 07:36:36AM +0100, Christoph Hellwig wrote:
> mapping_set_error should only be called on 0 returns (which it ignores)
> or a negative error code.
> 
> writepage_cb ends up being able to call writepage_cb on the magic
> AOP_WRITEPAGE_ACTIVATE return value from ->writepage which means
> success but the caller needs to unlock the page.  Ignore that and
> just call mapping_set_error on negative errors.
> 
> (no fixes tag as this goes back more than 20 years over various renames
>  and refactors so I've given up chasing down the original introduction)
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---

Reviewed-by: Brian Foster <bfoster@...hat.com>

>  mm/page-writeback.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 3f255534986a2f..703e83c69ffe08 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2535,7 +2535,9 @@ static int writepage_cb(struct folio *folio, struct writeback_control *wbc,
>  {
>  	struct address_space *mapping = data;
>  	int ret = mapping->a_ops->writepage(&folio->page, wbc);
> -	mapping_set_error(mapping, ret);
> +
> +	if (ret < 0)
> +		mapping_set_error(mapping, ret);
>  	return ret;
>  }
>  
> -- 
> 2.39.2
> 
>