Btrfs: don't clear the default compression type
authorMiao Xie <miaox@cn.fujitsu.com>
Fri, 22 Nov 2013 10:47:59 +0000 (18:47 +0800)
committerChris Mason <clm@fb.com>
Thu, 12 Dec 2013 15:11:19 +0000 (07:11 -0800)
commita7e252af5a819eb71c9494e62b2bfca982e92f84
tree73554777e84f56b52adbfe58a52cb6b370ecbcdd
parentc0778e2534b81be6b85b5ee07c0e15ff774f7136
Btrfs: don't clear the default compression type

We met a oops caused by the wrong compression type:
[  556.512356] BUG: unable to handle kernel NULL pointer dereference at           (null)
[  556.512370] IP: [<ffffffff811dbaa0>] __list_del_entry+0x1/0x98
[SNIP]
[  556.512490]  [<ffffffff811dbb44>] ? list_del+0xd/0x2b
[  556.512539]  [<ffffffffa05dd5ce>] find_workspace+0x97/0x175 [btrfs]
[  556.512546]  [<ffffffff813c14b5>] ? _raw_spin_lock+0xe/0x10
[  556.512576]  [<ffffffffa05de276>] btrfs_compress_pages+0x2d/0xa2 [btrfs]
[  556.512601]  [<ffffffffa05af060>] compress_file_range.constprop.54+0x1f2/0x4e8 [btrfs]
[  556.512627]  [<ffffffffa05af388>] async_cow_start+0x32/0x4d [btrfs]
[  556.512655]  [<ffffffffa05cc7a1>] worker_loop+0x144/0x4c3 [btrfs]
[  556.512661]  [<ffffffff81059404>] ? finish_task_switch+0x80/0xb8
[  556.512689]  [<ffffffffa05cc65d>] ? btrfs_queue_worker+0x244/0x244 [btrfs]
[  556.512695]  [<ffffffff8104fa4e>] kthread+0x8d/0x95
[  556.512699]  [<ffffffff81050000>] ? bit_waitqueue+0x34/0x7d
[  556.512704]  [<ffffffff8104f9c1>] ? __kthread_parkme+0x65/0x65
[  556.512709]  [<ffffffff813c7eec>] ret_from_fork+0x7c/0xb0
[  556.512713]  [<ffffffff8104f9c1>] ? __kthread_parkme+0x65/0x65

Steps to reproduce:
 # mkfs.btrfs -f <dev>
 # mount -o nodatacow <dev> <mnt>
 # touch <mnt>/<file>
 # chattr =c <mnt>/<file>
 # dd if=/dev/zero of=<mnt>/<file> bs=1M count=10

It is because we cleared the default compression type when setting the
nodatacow. In fact, we needn't do it because we have used COMPRESS flag to
indicate if we need compressed the file data or not, needn't use the
variant -- compress_type -- in btrfs_info to do the same thing, and just
use it to hold the default compression type. Or we would get a wrong compress
type for a file whose own compress flag is set but the compress flag of its
filesystem is not set.

Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Chris Mason <clm@fb.com>
fs/btrfs/super.c