Re: WARN_ON in record_root_in_trans() when deleting freshly renamed subvolume

[Filipe Manana <fdmanana@gmail.com>]

On Thu, Apr 7, 2016 at 5:44 PM, Holger Hoffstätte
<holger.hoffstaette@googlemail.com> wrote:
> 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

Haven't tried, but by taking a glance at btrfs_rename(), if you call
sync (or force a transaction commit through some other means) after
the rename and before deleting the snapshot, the warning should not
happen.

> $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,

Which can't solve this warning nor cause it, since you didn't fsync
and trigger the replay of the log trees.

> so maybe it's a corner case or an older problem. I'll try to bisect, but
> meanwhile wanted to report it for discussion.

Seems like an old problem to me.

Thanks for reporting it!

>
> Holger
>
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-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."