queue-2.6.33/ext4-fix-bug_on-in-ext4_ext_insert_extent.patch

From gnehzuil.liu@gmail.com  Thu Nov  3 10:42:14 2011
From: Zheng Liu <gnehzuil.liu@gmail.com>
Date: Fri, 28 Oct 2011 20:34:02 +0800
Subject: ext4: fix BUG_ON() in ext4_ext_insert_extent()
To: Greg KH <greg@kroah.com>
Cc: Ted Ts'o <tytso@mit.edu>, Tao Ma <tm@tao.ma>, linux-ext4@vger.kernel.org, Xiaoyun Mao <xiaoyun.maoxy@aliyun-inc.com>, Yingbin Wang <yingbin.wangyb@aliyun-inc.com>, Jia Wan <jia.wanj@aliyun-inc.com>
Message-ID: <20111028123402.GA26003@gmail.com>


From: Zheng Liu <wenqing.lz@taobao.com>

Does not corrispond with a direct commit in Linus's tree as it was fixed
differently in the 3.0 release.


We will meet with a BUG_ON() if following script is run.

mkfs.ext4 -b 4096 /dev/sdb1 1000000
mount -t ext4 /dev/sdb1 /mnt/sdb1
fallocate -l 100M /mnt/sdb1/test
sync
for((i=0;i<170;i++))
do
        dd if=/dev/zero of=/mnt/sdb1/test conv=notrunc bs=256k count=1
seek=`expr $i \* 2`
done
umount /mnt/sdb1
mount -t ext4 /dev/sdb1 /mnt/sdb1
dd if=/dev/zero of=/mnt/sdb1/test conv=notrunc bs=256k count=1 seek=341
umount /mnt/sdb1
mount /dev/sdb1 /mnt/sdb1
dd if=/dev/zero of=/mnt/sdb1/test conv=notrunc bs=256k count=1 seek=340
sync

The reason is that it forgot to mark dirty when splitting two extents in
ext4_ext_convert_to_initialized(). Althrough ex has been updated in
memory, it is not dirtied both in ext4_ext_convert_to_initialized() and
ext4_ext_insert_extent(). The disk layout is corrupted. Then it will
meet with a BUG_ON() when writting at the start of that extent again.

Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Xiaoyun Mao <xiaoyun.maoxy@aliyun-inc.com>
Cc: Yingbin Wang <yingbin.wangyb@aliyun-inc.com>
Cc: Jia Wan <jia.wanj@aliyun-inc.com>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 fs/ext4/extents.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2566,6 +2566,7 @@ static int ext4_ext_convert_to_initializ
 		ex1 = ex;
 		ex1->ee_len = cpu_to_le16(iblock - ee_block);
 		ext4_ext_mark_uninitialized(ex1);
+		ext4_ext_dirty(handle, inode, path + depth);
 		ex2 = &newex;
 	}
 	/*