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

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

[Theodore Ts'o]

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.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.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;
-- 
2.0.0

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

[Lukáš Czerner]

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

> Date: Sat,  5 Jul 2014 16:28:51 -0400
> From: Theodore Ts'o <tytso@mit.edu>
> To: Ext4 Developers List <linux-ext4@vger.kernel.org>
> Cc: Theodore Ts'o <tytso@mit.edu>, stable@vger.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@redhat.com>

> 
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> Cc: stable@vger.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;
>