On current TW. following seems to be occuring when quotas are enabled and
snapper is used (and deleting snapshots).
[320344.131801] ------------[ cut here ]------------
[320344.131865] WARNING: CPU: 1 PID: 330 at ../fs/btrfs/qgroup.c:1414
btrfs_delayed_qgroup_accounting+0x543/0xe40 [btrfs]()
[320344.131869] Modules linked in: fuse tun sit tunnel4 ip_tunnel iscsi_ibft
iscsi_boot_sysfs bluetooth af_packet msr cpufreq_stats w83627ehf hwmon_vid
nls_iso8859_1 nls_cp437 vfat fat iTCO_wdt iTCO_vendor_support ppdev dm_mod arc4
rt2800pci rt2800mmio rt2800lib rt2x00pci rt2x00mmio rt2x00lib cuname -r
4.0.5-1-default
oretemp mac80211 serio_raw pcspkr snd_hda_codec_realtek snd_hda_codec_generic
snd_hda_intel i2c_i801 snd_hda_controller cfg80211 lpc_ich mfd_core
eeprom_93cx6 crc_ccitt rfkill snd_hda_codec snd_hwdep shpchp snd_pcm snd_timer
snd parport_pc tpm_infineon 8250_fintek parport tpm_tis soundcore tpm
acpi_cpufreq button processor btrfs xor raid6_pq sr_mod cdrom ehci_pci uhci_hcd
ehci_hcd e1000e ptp pps_core usbcore usb_common video sg efivarfs
[320344.131947] CPU: 1 PID: 330 Comm: btrfs-cleaner Not tainted 4.0.5-1-default
#1
[320344.131951] Hardware name: /D2500CC, BIOS
CCCDT10N.86A.0040.2014.0520.1400 05/20/2014
[320344.131954] 0000000000000000 ffffffffa0251d91 ffffffff81629bec
0000000000000000
[320344.131961] ffffffff81062f21 ffff880129fec000 ffff88008263ca40
ffff880006c6d240
[320344.131966] ffff8800ce0099c8 0000000000000000 ffffffffa0235a23
ffff8800369f3cdc
[320344.131972] Call Trace:
[320344.131995] [<ffffffff81005635>] dump_trace+0x85/0x330
[320344.132005] [<ffffffff81005973>] show_stack_log_lvl+0x93/0x170
[320344.132014] [<ffffffff81007031>] show_stack+0x21/0x50
[320344.132024] [<ffffffff81629bec>] dump_stack+0x40/0x50
[320344.132035] [<ffffffff81062f21>] warn_slowpath_common+0x81/0xb0
[320344.132076] [<ffffffffa0235a23>]
btrfs_delayed_qgroup_accounting+0x543/0xe40 [btrfs]
[320344.132114] [<ffffffffa01c0957>]
btrfs_run_delayed_refs.part.66+0x207/0x280 [btrfs]
[320344.132150] [<ffffffffa01d08e1>] btrfs_should_end_transaction+0x41/0x70
[btrfs]
[320344.132183] [<ffffffffa01beed8>] btrfs_drop_snapshot+0x458/0x860 [btrfs]
[320344.132219] [<ffffffffa01d0d9c>]
btrfs_clean_one_deleted_snapshot+0xac/0x100 [btrfs]
[320344.132251] [<ffffffffa01c9e9c>] cleaner_kthread+0x12c/0x190 [btrfs]
[320344.132263] [<ffffffff8107fce1>] kthread+0xc1/0xe0
[320344.132272] [<ffffffff8162ff98>] ret_from_fork+0x58/0x90
[320344.132280] ---[ end trace 9bacbb5026d14829 ]---
uname -r
4.0.5-1-default