Hi,
Looks like I just found an exciting new corner case.
kernel 4.4.6 with btrfs ~4.6, so 4.6 should reproduce.
Try on a fresh volume:
$btrfs subvolume create foo
Create subvolume './foo'
$sync
$btrfs subvolume snapshot foo foo-1
Create a snapshot of 'foo' in './foo-1'
$sync
$mv foo-1 foo.new
$btrfs subvolume delete foo.new
Delete subvolume (no-commit): '/mnt/test/foo.new'
$dmesg
[ 226.923316] ------------[ cut here ]------------
[ 226.923339] WARNING: CPU: 1 PID: 5863 at fs/btrfs/transaction.c:319
record_root_in_trans+0xd6/0x100 [btrfs]()
[ 226.923340] Modules linked in: auth_rpcgss oid_registry nfsv4 btrfs xor
raid6_pq loop nfs lockd grace sunrpc autofs4 sch_fq_codel radeon
snd_hda_codec_realtek x86_pkg_temp_thermal snd_hda_codec_generic coretemp
crc32_pclmul crc32c_intel aesni_intel i2c_algo_bit uvcvideo snd_hda_codec_hdmi
aes_x86_64 drm_kms_helper videobuf2_vmalloc glue_helper videobuf2_memops
syscopyarea lrw sysfillrect gf128mul videobuf2_v4l2 sysimgblt snd_usb_audio
fb_sys_fops ablk_helper snd_hda_intel videobuf2_core ttm cryptd snd_hwdep
v4l2_common usbhid snd_hda_codec snd_usbmidi_lib videodev snd_rawmidi drm
snd_hda_core snd_seq_device i2c_i801 snd_pcm i2c_core snd_timer snd r8169
soundcore mii parport_pc parport
[ 226.923365] CPU: 1 PID: 5863 Comm: ls Not tainted 4.4.6 #1
[ 226.923366] Hardware name: Gigabyte Technology Co., Ltd.
P67-DS3-B3/P67-DS3-B3, BIOS F1 05/06/2011
[ 226.923367] 0000000000000000 ffff8800da677d20 ffffffff813181a8
0000000000000000
[ 226.923368] ffffffffa0aacdbf ffff8800da677d58 ffffffff810507b2
ffff880601e90800
[ 226.923369] ffff8800dacf10a0 ffff880601e90800 ffff880601e909f0
0000000000000001
[ 226.923371] Call Trace:
[ 226.923374] [<ffffffff813181a8>] dump_stack+0x4d/0x65
[ 226.923376] [<ffffffff810507b2>] warn_slowpath_common+0x82/0xc0
[ 226.923378] [<ffffffff810508aa>] warn_slowpath_null+0x1a/0x20
[ 226.923387] [<ffffffffa0a2cf46>] record_root_in_trans+0xd6/0x100 [btrfs]
[ 226.923395] [<ffffffffa0a2db24>] btrfs_record_root_in_trans+0x44/0x70
[btrfs]
[ 226.923404] [<ffffffffa0a2fb5e>] start_transaction+0x9e/0x4c0 [btrfs]
[ 226.923412] [<ffffffffa0a2ffd7>] btrfs_join_transaction+0x17/0x20 [btrfs]
[ 226.923421] [<ffffffffa0a359b5>] btrfs_dirty_inode+0x35/0xd0 [btrfs]
[ 226.923430] [<ffffffffa0a35acd>] btrfs_update_time+0x7d/0xb0 [btrfs]
[ 226.923432] [<ffffffff81187028>] touch_atime+0x88/0xa0
[ 226.923434] [<ffffffff8117ec9b>] iterate_dir+0xdb/0x120
[ 226.923435] [<ffffffff8117f0c8>] SyS_getdents+0x88/0xf0
[ 226.923437] [<ffffffff8117edb0>] ? fillonedir+0xd0/0xd0
[ 226.923439] [<ffffffff815b8257>] entry_SYSCALL_64_fastpath+0x12/0x6a
[ 226.923440] ---[ end trace 9c78caf253e284fe ]---
Code looks like:
..
static int record_root_in_trans(struct btrfs_trans_handle *trans,
struct btrfs_root *root)
{
if (test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
root->last_trans < trans->transid) {
WARN_ON(root == root->fs_info->extent_root);
WARN_ON(root->commit_root != root->node);
..
There's been a few journal/recovery/directory consistency patches recently,
so maybe it's a corner case or an older problem. I'll try to bisect, but
meanwhile wanted to report it for discussion.
Holger
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