BZ 742091
https://bugzilla.redhat.com/show_bug.cgi?id=742091
This bug was never properly fixed upstream since the code got
reorganized in:
667eff35a1f56fa74ce98a0c7c29a40adc1ba4e3 ext4: reimplement convert and
split_unwritten
This fix has proposed by Zheng Liu <wenqing.lz@taobao.com>, then updated,
reviewed and tested by me.
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.
Originally-from: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
---
fs/ext4/extents.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
Index: linux-2.6.35.noarch/fs/ext4/extents.c
===================================================================
--- linux-2.6.35.noarch.orig/fs/ext4/extents.c
+++ linux-2.6.35.noarch/fs/ext4/extents.c
@@ -2687,6 +2687,7 @@ static int ext4_ext_convert_to_initializ
ex1 = ex;
ex1->ee_len = cpu_to_le16(map->m_lblk - ee_block);
ext4_ext_mark_uninitialized(ex1);
+ ext4_ext_dirty(handle, inode, path + depth);
ex2 = &newex;
}
/*
@@ -2850,6 +2851,7 @@ static int ext4_ext_convert_to_initializ
ex1 = ex;
ex1->ee_len = cpu_to_le16(map->m_lblk - ee_block);
ext4_ext_mark_uninitialized(ex1);
+ ext4_ext_dirty(handle, inode, path + depth);
ex2 = &newex;
}
/* ex2: map->m_lblk to map->m_lblk + maxblocks-1 : initialised */