linux-ext4 - Re: [PATCH v2] ext4: Fix bdev write error check failed when mount fs with ro

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Date:   Fri, 25 Sep 2020 11:10:02 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Xiaoxu <zhangxiaoxu5@...wei.com>
Cc:     yi.zhang@...wei.com, tytso@....edu, jack@...e.cz,
        linux-ext4@...r.kernel.org, adilger.kernel@...ger.ca
Subject: Re: [PATCH v2] ext4: Fix bdev write error check failed when mount fs
 with ro

On Thu 24-09-20 21:01:42, Zhang Xiaoxu wrote:
> If some errors has occurred on the device, and the orphan list not empty,
> then mount the device with 'ro', the bdev write error check will failed:
>   ext4_check_bdev_write_error:193: comm mount: Error while async write back metadata
> 
> Since the sbi->s_bdev_wb_err wouldn't be initialized when mount file system
> with 'ro', when clean up the orphan list and access the iloc buffer, bdev
> write error check will failed.
>
> So we should always initialize the sbi->s_bdev_wb_err even if mount the
> file system with 'ro'.

Let me rephrase the changelog a little bit for better readability:

Consider a situation when a filesystem was uncleanly shutdown and the orphan
list is not empty and a read-only mount is attempted. The orphan list
cleanup during mount will fail with:

ext4_check_bdev_write_error:193: comm mount: Error while async write back metadata

This happens because sbi->s_bdev_wb_err is not initialized when mounting
the filesystem in read only mode and so ext4_check_bdev_write_error()
falsely triggers.

Initialize sbi->s_bdev_wb_err unconditionally to avoid this problem.

> 
> Fixes: bc71726c7257 ("ext4: abort the filesystem if failed to async write metadata buffer")
> Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@...wei.com>

Otherwise the patch looks good so feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza


> ---
>  fs/ext4/super.c | 13 ++-----------
>  1 file changed, 2 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index ea425b49b345..0303e6e17190 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4814,9 +4814,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  	 * used to detect the metadata async write error.
>  	 */
>  	spin_lock_init(&sbi->s_bdev_wb_lock);
> -	if (!sb_rdonly(sb))
> -		errseq_check_and_advance(&sb->s_bdev->bd_inode->i_mapping->wb_err,
> -					 &sbi->s_bdev_wb_err);
> +	errseq_check_and_advance(&sb->s_bdev->bd_inode->i_mapping->wb_err,
> +				 &sbi->s_bdev_wb_err);
>  	sb->s_bdev->bd_super = sb;
>  	EXT4_SB(sb)->s_mount_state |= EXT4_ORPHAN_FS;
>  	ext4_orphan_cleanup(sb, es);
> @@ -5707,14 +5706,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>  				goto restore_opts;
>  			}
>  
> -			/*
> -			 * Update the original bdev mapping's wb_err value
> -			 * which could be used to detect the metadata async
> -			 * write error.
> -			 */
> -			errseq_check_and_advance(&sb->s_bdev->bd_inode->i_mapping->wb_err,
> -						 &sbi->s_bdev_wb_err);
> -
>  			/*
>  			 * Mounting a RDONLY partition read-write, so reread
>  			 * and store the current valid flag.  (It may have
> -- 
> 2.25.4
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR