linux-ext4 - Re: [PATCH] ext4: fix unjournalled bg descriptor while initializing inode bitmap

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Date:	Tue, 8 Jul 2014 08:46:14 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	stable@...r.kernel.org
Subject: Re: [PATCH] ext4: fix unjournalled bg descriptor while initializing
 inode bitmap

On Sat, 5 Jul 2014, Theodore Ts'o wrote:

> Date: Sat,  5 Jul 2014 16:28:51 -0400
> From: Theodore Ts'o <tytso@....edu>
> To: Ext4 Developers List <linux-ext4@...r.kernel.org>
> Cc: Theodore Ts'o <tytso@....edu>, stable@...r.kernel.org
> Subject: [PATCH] ext4: fix unjournalled bg descriptor while initializing inode
>      bitmap
> 
> The first time that we allocate from an uninitialized inode allocation
> bitmap, if the block allocation bitmap is also uninitalized, we need
> to get write access to the block group descriptor before we start
> modifying the block group descriptor flags and updating the free block
> count, etc.  Otherwise, there is the potential of a bad journal
> checksum (if journal checksums are enabled), and of the file system
> becoming inconsistent if we crash at exactly the wrong time.

Looks good.

Reviewed-by: Lukas Czerner <lczerner@...hat.com>

> 
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> Cc: stable@...r.kernel.org
> ---
>  fs/ext4/ialloc.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
> index a87455d..0840bf3 100644
> --- a/fs/ext4/ialloc.c
> +++ b/fs/ext4/ialloc.c
> @@ -874,6 +874,13 @@ got:
>  		goto out;
>  	}
>  
> +	BUFFER_TRACE(group_desc_bh, "get_write_access");
> +	err = ext4_journal_get_write_access(handle, group_desc_bh);
> +	if (err) {
> +		ext4_std_error(sb, err);
> +		goto out;
> +	}
> +
>  	/* We may have to initialize the block bitmap if it isn't already */
>  	if (ext4_has_group_desc_csum(sb) &&
>  	    gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
> @@ -910,13 +917,6 @@ got:
>  		}
>  	}
>  
> -	BUFFER_TRACE(group_desc_bh, "get_write_access");
> -	err = ext4_journal_get_write_access(handle, group_desc_bh);
> -	if (err) {
> -		ext4_std_error(sb, err);
> -		goto out;
> -	}
> -
>  	/* Update the relevant bg descriptor fields */
>  	if (ext4_has_group_desc_csum(sb)) {
>  		int free;
> 
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