linux-kernel - Re: [PATCH v2 5/6] iomap: don't mark blocks uptodate after partial zeroing

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Message-ID: <20240812164912.GF6043@frogsfrogsfrogs>
Date: Mon, 12 Aug 2024 09:49:12 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org, brauner@...nel.org,
	david@...morbit.com, jack@...e.cz, willy@...radead.org,
	yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v2 5/6] iomap: don't mark blocks uptodate after partial
 zeroing

On Mon, Aug 12, 2024 at 08:11:58PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> In __iomap_write_begin(), if we unaligned buffered write data to a hole
> of a regular file, we only zero out the place where aligned to block
> size that we don't want to write, but mark the whole range uptodate if
> block size < folio size. This is wrong since the not zeroed part will
> contains stale data and can be accessed by a concurrent buffered read
> easily (on the filesystem may not hold inode->i_rwsem) once we mark the
> range uptodate. Fix this by drop iomap_set_range_uptodate() in the
> zeroing out branch.
> 
> Fixes: 9dc55f1389f9 ("iomap: add support for sub-pagesize buffered I/O without buffer heads")
> Reported-by: Matthew Wilcox <willy@...radead.org>
> Closes: https://lore.kernel.org/all/ZqsN5ouQTEc1KAzV@casper.infradead.org/
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> ---
>  fs/iomap/buffered-io.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index ac762de9a27f..96600405dbb5 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -744,8 +744,8 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
>  					poff, plen, srcmap);
>  			if (status)
>  				return status;
> +			iomap_set_range_uptodate(folio, poff, plen);
>  		}
> -		iomap_set_range_uptodate(folio, poff, plen);

Don't we need to iomap_set_range_uptodate for the bytes that we zeroed
with folio_zero_segments?

--D

>  	} while ((block_start += plen) < block_end);
>  
>  	return 0;
> -- 
> 2.39.2
> 
>