ext4: fix the free blocks calculation for ext3 file systems w/ uninit_bg
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 fd034a84 , present since v3.2). Reported-by: Sander Eikelenboom <linux@eikelenboom.it> Reported-by: Kees Cook <keescook@chromium.org> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Tested-by: Kees Cook <keescook@chromium.org> Cc: stable@kernel.org
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