On Fri, Jan 24, 2014 at 02:55:57AM +0000, Akira Fujita wrote: > When meta_bg feature is enabled, group descriptor block is allocated > every 128 block group (or every 64 block group if 64bit feature is enabled). > > In such situation, files in block group more than #128 will be removed > if sparse_super feature is enabled with tune2fs and > afterwards necessary e2fsck running. > > Because tune2fs does not reallocate group descriptor blocks > but just set sparse_super feature. > If ext4 has sparse_super, ext2fs_descriptor_block_loc2() called > by e2fsck thinks the block group (e.g. #128) that it has group descriptor block > at the head offset. But that offset is used as backup super block before. > So e2fsck fixes ext4 based on invalid group descriptor blocks and this > cause data lost. > > The patch avoids this problem simply by disallow tune2fs enabling > sparse_super if meta_bg is enabled. > > Steps to reproduce: > > 1. Create ext4 which has meta_bg, ^sparse_super and 129+ block groups. > # mke2fs -t ext4 -O meta_bg,^resize_inode,^sparse_super DEV 17G > # mount DEV /MP > > 2. Create direcotry and files which use block group #128's metadata. > # echo $((8192*128+1)) > /sys/fs/ext4/DEV/inode_goal > # mkdir /MP/DIR > # for i in $(seq 1 100); do dd if=/dev/urandom of=/MP/DIR/file$i bs=1024 count=10; done > > 3. Enable sparse_super with tune2fs then execute e2fsck. > Data in block group #128 will be lost!! > # umount DEV > # tune2fs -O sparse_super DEV > # e2fsck/e2fsck -yf DEV > > Signed-off-by: Akira Fujita <a-fujita@xxxxxxxxxxxxx> Applied, thanks. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
