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>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 2d8ac1bf0cf9b9d613215000758cbfa312b4962e..d71a11d13dfaa8b3065222c87ce964d8ba28e5b5 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -432,7 +432,6 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
                        } else {
                                printk(KERN_INFO "btrfs: setting nodatacow\n");
                        }
-                       info->compress_type = BTRFS_COMPRESS_NONE;
                        btrfs_clear_opt(info->mount_opt, COMPRESS);
                        btrfs_clear_opt(info->mount_opt, FORCE_COMPRESS);
                        btrfs_set_opt(info->mount_opt, NODATACOW);
@@ -461,7 +460,6 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
                                btrfs_set_fs_incompat(info, COMPRESS_LZO);
                        } else if (strncmp(args[0].from, "no", 2) == 0) {
                                compress_type = "no";
-                               info->compress_type = BTRFS_COMPRESS_NONE;
                                btrfs_clear_opt(info->mount_opt, COMPRESS);
                                btrfs_clear_opt(info->mount_opt, FORCE_COMPRESS);
                                compress_force = false;
@@ -474,9 +472,10 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
                                btrfs_set_opt(info->mount_opt, FORCE_COMPRESS);
                                pr_info("btrfs: force %s compression\n",
                                        compress_type);
-                       } else
+                       } else if (btrfs_test_opt(root, COMPRESS)) {
                                pr_info("btrfs: use %s compression\n",
                                        compress_type);
+                       }
                        break;
                case Opt_ssd:
                        printk(KERN_INFO "btrfs: use ssd allocation scheme\n");