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@xxxxxxxxxxxxxx> Signed-off-by: Miao Xie <miaox@xxxxxxxxxxxxxx> --- fs/btrfs/super.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index fb62c45..fd05d7a 100644 --- 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"); -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html