Ack: Re: [Quantal][Precise SRU][PATCH 1/1] UBUNTU: SAUCE: ext4: fix the free blocks calculation for ext3 file systems w/ uninit_bg

[Herton Ronaldo Krzesinski]

On Thu, Jun 07, 2012 at 06:19:14PM +0100, Luis Henriques wrote:
> From: Theodore Ts'o <tytso at mit.edu>
> 
> BugLink: http://bugs.launchpad.net/bugs/1010022
> 
> Ext3 filesystems that are converted to use as many ext4 file system
> features as possible will enable uninit_bg to speed up e2fsck times.
> These file systems will have a native ext3 layout of inode tables and
> block allocation bitmaps (as opposed to ext4's flex_bg layout).
> Unfortunately, in these cases, when first allocating a block in an
> uninitialized block group, ext4 would incorrectly calculate the number
> of free blocks in that block group, and then errorneously report that
> the file system was corrupt:
> 
> EXT4-fs error (device vdd): ext4_mb_generate_buddy:741: group 30, 32254 clusters in bitmap, 32258 in gd
> 
> This problem can be reproduced via:
> 
>     mke2fs -q -t ext4 -O ^flex_bg /dev/vdd 5g
>     mount -t ext4 /dev/vdd /mnt
>     fallocate -l 4600m /mnt/test
> 
> The problem was caused by a bone headed mistake in the check to see if a
> particular metadata block was part of the block group.
> 
> Many thanks to Kees Cook for finding and bisecting the buggy commit
> which introduced this bug (commit fd034a84e1, present since v3.2).
> 
> Reported-by: Sander Eikelenboom <linux at eikelenboom.it>
> Reported-by: Kees Cook <keescook at chromium.org>
> Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
> Cc: stable at kernel.org
> Cc: Sander Eikelenboom <linux at eikelenboom.it>
> Cc: Kees Cook <keescook at chromium.org>
> 
> Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
> ---
>  fs/ext4/balloc.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> index 12ccacd..914bf9e 100644
> --- a/fs/ext4/balloc.c
> +++ b/fs/ext4/balloc.c
> @@ -88,8 +88,8 @@ unsigned ext4_num_overhead_clusters(struct super_block *sb,
>  	 * unusual file system layouts.
>  	 */
>  	if (ext4_block_in_group(sb, ext4_block_bitmap(sb, gdp), block_group)) {
> -		block_cluster = EXT4_B2C(sbi, (start -
> -					       ext4_block_bitmap(sb, gdp)));
> +		block_cluster = EXT4_B2C(sbi,
> +					 ext4_block_bitmap(sb, gdp) - start);
>  		if (block_cluster < num_clusters)
>  			block_cluster = -1;
>  		else if (block_cluster == num_clusters) {
> @@ -100,7 +100,7 @@ unsigned ext4_num_overhead_clusters(struct super_block *sb,
>  
>  	if (ext4_block_in_group(sb, ext4_inode_bitmap(sb, gdp), block_group)) {
>  		inode_cluster = EXT4_B2C(sbi,
> -					 start - ext4_inode_bitmap(sb, gdp));
> +					 ext4_inode_bitmap(sb, gdp) - start);
>  		if (inode_cluster < num_clusters)
>  			inode_cluster = -1;
>  		else if (inode_cluster == num_clusters) {
> @@ -112,7 +112,7 @@ unsigned ext4_num_overhead_clusters(struct super_block *sb,
>  	itbl_blk = ext4_inode_table(sb, gdp);
>  	for (i = 0; i < sbi->s_itb_per_group; i++) {
>  		if (ext4_block_in_group(sb, itbl_blk + i, block_group)) {
> -			c = EXT4_B2C(sbi, start - itbl_blk + i);
> +			c = EXT4_B2C(sbi, itbl_blk + i - start);
>  			if ((c < num_clusters) || (c == inode_cluster) ||
>  			    (c == block_cluster) || (c == itbl_cluster))
>  				continue;
> -- 
> 1.7.9.5
> 
> 
> -- 
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> 

-- 
[]'s
Herton