linux-ext4 - Re: [PATCH] fs/buffer.c: Fix data corruption when buffer write with IO error

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Date:   Mon, 8 Apr 2019 13:11:08 +0200
From:   Jan Kara <jack@...e.cz>
To:     ZhangXiaoxu <zhangxiaoxu5@...wei.com>
Cc:     viro@...iv.linux.org.uk, tytso@....edu, adilger.kernel@...ger.ca,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH] fs/buffer.c: Fix data corruption when buffer write with
 IO error

On Sat 06-04-19 15:13:13, ZhangXiaoxu wrote:
> When the buffer write failed, 'end_buffer_write_sync' and
> 'end_buffer_async_write' will clear the uptodate flag. But the
> data in the buffer maybe newer than disk. In some case, this
> will lead data corruption.
> 
> For example: ext4 flush metadata to disk failed, it will clear
> the uptodate flag. when a new coming call want the buffer, it will
> read it from the disk(because the buffer no uptodate flag). But
> the journal not checkpoint now, it will read old data from disk.
> If read successfully, ext4 will write the old data to the new
> journal, the data will corruption.
> 
> So, don't clear the uptodate flag when write the buffer failed.
> 
> Signed-off-by: ZhangXiaoxu <zhangxiaoxu5@...wei.com>

Thanks for the patch. But what are the chances that after the write has
failed the read will succeed? Also there were places that were using
buffer_uptodate() to detect IO errors. Did you check all those got
converted to using buffer_write_io_error() instead?

								Honza

> ---
>  fs/buffer.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index ce35760..9fe1827 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -172,7 +172,6 @@ void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
>  	} else {
>  		buffer_io_error(bh, ", lost sync page write");
>  		mark_buffer_write_io_error(bh);
> -		clear_buffer_uptodate(bh);
>  	}
>  	unlock_buffer(bh);
>  	put_bh(bh);
> @@ -325,7 +324,6 @@ void end_buffer_async_write(struct buffer_head *bh, int uptodate)
>  	} else {
>  		buffer_io_error(bh, ", lost async page write");
>  		mark_buffer_write_io_error(bh);
> -		clear_buffer_uptodate(bh);
>  		SetPageError(page);
>  	}
>  
> -- 
> 2.7.4
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR