Commit a7e252af authored Nov 22, 2013 by Miao Xie Committed by Chris Mason Dec 12, 2013

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>

parent c0778e25

fs/btrfs/super.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -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");

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