I'm seeing this too, with kernel 5.5.8. It starts almost immediately after remounting with flushoncommit. [1098047.402847] fnuc.local kernel: BTRFS info (device sdb2): turning on flush-on-commit [1098047.402856] fnuc.local kernel: BTRFS info (device sdb2): disabling tree log [1098047.402861] fnuc.local kernel: BTRFS info (device sdb2): using free space tree [1098053.747527] fnuc.local kernel: BTRFS info (device dm-0): turning on flush-on-commit [1098053.747535] fnuc.local kernel: BTRFS info (device dm-0): disabling tree log [1098053.747538] fnuc.local kernel: BTRFS info (device dm-0): using free space tree [1098077.413093] fnuc.local kernel: ------------[ cut here ]------------ [1098077.413131] fnuc.local kernel: WARNING: CPU: 2 PID: 379 at fs/fs-writeback.c:2466 __writeback_inodes_sb_nr+0xc0/0xd0 [1098077.413136] fnuc.local kernel: Modules linked in: cdc_acm dm_crypt nf_conntrack_netbios_ns nf_conntrack_broadcast xt_CT ip6t_REJECT nf_reject_ipv6 ip6t_rpfilter ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ebtable_broute ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat iptable_mangle iptable_raw iptable_security nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nfnetlink ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter cmac bnep sunrpc snd_hda_codec_hdmi intel_rapl_msr snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio mei_hdcp snd_hda_intel intel_rapl_common snd_intel_dspcfg intel_powerclamp iTCO_wdt coretemp iTCO_vendor_support snd_hda_codec kvm_intel iwlmvm mac80211 kvm snd_hda_core libarc4 btusb irqbypass snd_hwdep snd_seq crct10dif_pclmul iwlwifi btrtl crc32_pclmul btbcm snd_seq_device btintel snd_pcm ghash_clmulni_intel bluetooth intel_cstate cfg80211 snd_timer snd ecdh_generic ecc soundcore r8169 mei_txe intel_xhci_usb_role_switch mei rfkill [1098077.413395] fnuc.local kernel: roles i2c_i801 lpc_ich dw_dmac intel_int0002_vgpio vfat fat binfmt_misc zram ip_tables btrfs blake2b_generic libcrc32c xor zstd_decompress zstd_compress raid6_pq i915 i2c_algo_bit crc32c_intel drm_kms_helper drm uas usb_storage sdhci_acpi sdhci video mmc_core pwm_lpss_platform pwm_lpss fuse [1098077.413515] fnuc.local kernel: CPU: 2 PID: 379 Comm: btrfs-transacti Not tainted 5.5.8-200.fc31.x86_64 #1 [1098077.413522] fnuc.local kernel: Hardware name: /NUC5PPYB, BIOS PYBSWCEL.86A.0078.2019.0807.1133 08/07/2019 [1098077.413539] fnuc.local kernel: RIP: 0010:__writeback_inodes_sb_nr+0xc0/0xd0 [1098077.413553] fnuc.local kernel: Code: 0f b6 d1 48 8d 74 24 10 e8 6d fc ff ff 48 89 e7 e8 e5 fb ff ff 48 8b 44 24 50 65 48 33 04 25 28 00 00 00 75 09 48 83 c4 58 c3 <0f> 0b eb cf e8 b7 38 d9 ff 0f 1f 80 00 00 00 00 0f 1f 44 00 00 31 [1098077.413561] fnuc.local kernel: RSP: 0018:ffffabed404a7df0 EFLAGS: 00010246 [1098077.413572] fnuc.local kernel: RAX: 0000000000000000 RBX: ffff8cc172cfc960 RCX: 0000000000000000 [1098077.413578] fnuc.local kernel: RDX: 0000000000000002 RSI: 0000000000001d2a RDI: ffff8cc17abf5000 [1098077.413585] fnuc.local kernel: RBP: ffff8cc176b84e38 R08: ffff8cc17666e800 R09: ffffabed404a7de8 [1098077.413592] fnuc.local kernel: R10: ffff8cc048cd3758 R11: 000000000003c000 R12: ffff8cc172cf0000 [1098077.413599] fnuc.local kernel: R13: ffff8cc13dc2a000 R14: ffff8cc172cfc938 R15: ffff8cc13dc2a000 [1098077.413608] fnuc.local kernel: FS: 0000000000000000(0000) GS:ffff8cc17bd00000(0000) knlGS:0000000000000000 [1098077.413614] fnuc.local kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [1098077.413621] fnuc.local kernel: CR2: 0000555defae5e90 CR3: 000000014b60a000 CR4: 00000000001006e0 [1098077.413626] fnuc.local kernel: Call Trace: [1098077.413820] fnuc.local kernel: btrfs_commit_transaction+0x303/0xa20 [btrfs] [1098077.413977] fnuc.local kernel: ? start_transaction+0xbb/0x4c0 [btrfs] [1098077.414124] fnuc.local kernel: transaction_kthread+0x13c/0x180 [btrfs] [1098077.414146] fnuc.local kernel: kthread+0xf9/0x130 [1098077.414292] fnuc.local kernel: ? btrfs_cleanup_transaction+0x5c0/0x5c0 [btrfs] [1098077.414306] fnuc.local kernel: ? kthread_park+0x90/0x90 [1098077.414323] fnuc.local kernel: ret_from_fork+0x35/0x40 [1098077.414340] fnuc.local kernel: ---[ end trace a3fc4c6144f1f7ae ]--- [1098107.620280] fnuc.local kernel: ------------[ cut here ]------------ -- Chris Murphy
