linux-ext4 - Re: [RESEND PATCH 2/2] ext3: flush journal only when journal mode is changed from journaled

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Message-ID: <20111115133305.GE21732@quack.suse.cz>
Date:	Tue, 15 Nov 2011 14:33:05 +0100
From:	Jan Kara <jack@...e.cz>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
Cc:	jack@...e.cz, linux-ext4@...r.kernel.org
Subject: Re: [RESEND PATCH 2/2] ext3: flush journal only when journal mode
 is changed from journaled

On Tue 15-11-11 16:04:49, Yongqiang Yang wrote:
> To prevent data from corruption during repaly, we need to flush journal
> before changing journal mode from journaled.  However flushing journal is
> not needed when changing journal to journaled.
  We flush the journal for other reasons as well - switching inodes
->i_aops is rather complex thing so a filesystem should better be in a
quiescent state. You'd definitely at least need to commit the running
transaction otherwise a hell would break loose if you tried to modify a
buffer both as ordered data and as metadata in one transaction.

  So I strongly prefer to keep the code as is unless you can really
convincingly *prove* that nothing breaks and show benefit of such change.

								Honza
> 
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
> ---
>  fs/ext3/inode.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
> index 04da6ac..5577358 100644
> --- a/fs/ext3/inode.c
> +++ b/fs/ext3/inode.c
> @@ -3546,7 +3546,6 @@ int ext3_change_inode_journal_flag(struct inode *inode, int val)
>  		return -EROFS;
>  
>  	journal_lock_updates(journal);
> -	journal_flush(journal);
>  
>  	/*
>  	 * OK, there are no updates running now, and all cached data is
> @@ -3556,10 +3555,12 @@ int ext3_change_inode_journal_flag(struct inode *inode, int val)
>  	 * the inode's in-core data-journaling state flag now.
>  	 */
>  
> -	if (val)
> +	if (val) {
>  		EXT3_I(inode)->i_flags |= EXT3_JOURNAL_DATA_FL;
> -	else
> +	} else {
> +		journal_flush(journal);
>  		EXT3_I(inode)->i_flags &= ~EXT3_JOURNAL_DATA_FL;
> +	}
>  	ext3_set_aops(inode);
>  
>  	journal_unlock_updates(journal);
> -- 
> 1.7.5.1
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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