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SubjectRe: EXT4-fs error (device dm-42): ext4_mb_generate_buddy:741: group 1904, 32254 clusters in bitmap, 32258 in gd
I think this patch should fix things.  Could you give it a try (after
re-enabling uninit_bg and then running e2fsck on the file systems)?

Many thanks,

- Ted

commit b6b218940d47f20fc14e4d203930c575be0c65bf
Author: Theodore Ts'o <tytso@mit.edu>
Date: Thu Jun 7 00:26:56 2012 -0400

ext4: fix the free blocks calculation for ext3 file systems w/ uninit_bg

Ext3 filesystems that are converted to use as many ext4 file systems
as possible will enable uninit_bg to speed up e2fsck times. File
systems with an native ext3 layout of inode tables and block
allocation bitmaps (as opposed to ext4's flex_bg layout), ext4 would
sometimes incorrectly calculate the number of free blocks in an
uninitialized block group. As a result, when first allocating a block
in block group marked uninitalized, ext4 would incorrectly report that
the file system was corrupt:

EXT4-fs error (device dm-42): ext4_mb_generate_buddy:741: group 1699, 32254 clusters in bitmap, 32258 in gd

Fix the calculation in ext4_num_overhead_clusters() to avoid this
problem.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 99b6324..cee7812 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -90,8 +90,8 @@ 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) {
@@ -102,7 +102,7 @@ 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) {
@@ -114,7 +114,7 @@ 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;

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