linux-ext4 - Re: [PATCH 3/3] ext4: Fix fsync error handling after filesystem abort.

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Date:	Mon, 10 Jun 2013 14:22:09 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz
Subject: Re: [PATCH 3/3] ext4: Fix fsync error handling after filesystem
 abort.

On Mon, Jun 10, 2013 at 08:41:01PM +0400, Dmitry Monakhov wrote:
> If filesystem was aborted after inode's write back is complete
> but before its metadata was updated we may return success
> results in data loss.
> In order to handle fs abort correctly we have to check
> fs state once we discover that it is in MS_RDONLY state
> 
> Test case: http://patchwork.ozlabs.org/patch/244297
> 
> Changes from V2:
>  - more spelling fixes
> 
> Changes from V1:
>  - fix spelling
> 
> Reviewed-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
> ---
>  fs/ext4/fsync.c |    7 ++++++-
>  fs/ext4/super.c |   12 +++++++++++-
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
> index fc938eb..a8bc47f 100644
> --- a/fs/ext4/fsync.c
> +++ b/fs/ext4/fsync.c
> @@ -98,8 +98,13 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
>  
>  	trace_ext4_sync_file_enter(file, datasync);
>  
> -	if (inode->i_sb->s_flags & MS_RDONLY)
> +	if (inode->i_sb->s_flags & MS_RDONLY) {
> +		/* Make sure that we read updated s_mount_flags value */
> +		smp_rmb();
> +		if (EXT4_SB(inode->i_sb)->s_mount_flags & EXT4_MF_FS_ABORTED)
> +			ret = -EROFS;
>  		goto out;
> +	}
>  
>  	if (!journal) {
>  		ret = generic_file_fsync(file, start, end, datasync);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 0f77c2e..f23daaa 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -399,6 +399,11 @@ static void ext4_handle_error(struct super_block *sb)
>  	}
>  	if (test_opt(sb, ERRORS_RO)) {
>  		ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
> +		/*
> +		 * Make shure updated value of ->s_mount_flags will be visible
> +		 * before ->s_flags update
> +		 */
> +		smp_wmb();
>  		sb->s_flags |= MS_RDONLY;
>  	}
>  	if (test_opt(sb, ERRORS_PANIC))
> @@ -571,8 +576,13 @@ void __ext4_abort(struct super_block *sb, const char *function,
>  
>  	if ((sb->s_flags & MS_RDONLY) == 0) {
>  		ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
> -		sb->s_flags |= MS_RDONLY;
>  		EXT4_SB(sb)->s_mount_flags |= EXT4_MF_FS_ABORTED;
> +		/*
> +		 * Make shure updated value of ->s_mount_flags will be visiable

I think you meant 'sure' and 'visible' here and in the previous hunk.

--D
> +		 * before ->s_flags update
> +		 */
> +		smp_wmb();
> +		sb->s_flags |= MS_RDONLY;
>  		if (EXT4_SB(sb)->s_journal)
>  			jbd2_journal_abort(EXT4_SB(sb)->s_journal, -EIO);
>  		save_error_info(sb, function, line);
> -- 
> 1.7.1
> 
> --
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