Am 31.03.21 um 03:58 schrieb Zygo Blaxell:

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WARNING: CPU: 1 PID: 314 at fs/fs-writeback.c:2472 __writeback_inodes_sb_nr+0xb8/0xd0
Modules linked in: iTCO_wdt wireguard curve25519_x86_64 libchacha20poly1305 intel_pmc_bxt iTCO_vendor_support chacha_x86_64 poly1305_x86_64 libblake2s blake2s_x86_64 ip6_udp_tunnel udp_tunnel libcurve25519_generic libchacha libblake2s_generic psmouse joydev mousedev pcspkr i2c_i801 i2c_smbus lpc_ich iptable_filter xt_nat xt_tcpudp intel_agp intel_gtt iptable_nat nf_nat qemu_fw_cfg nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 mac_hid vfat fat auth_rpcgss sunrpc fuse ip_tables x_tables btrfs blake2b_generic libcrc32c crc32c_generic xor raid6_pq dm_crypt cbc encrypted_keys trusted tpm usbhid dm_mod virtio_gpu virtio_dma_buf drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec drm virtio_scsi virtio_balloon virtio_net virtio_console net_failover agpgart failover crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel crypto_simd cryptd glue_helper serio_raw sr_mod cdrom xhci_pci virtio_pci virtio_rng rng_core
CPU: 1 PID: 314 Comm: btrfs-transacti Tainted: G        W         5.10.26-1-MANJARO #1
Hardware name: Hetzner vServer, BIOS 20171111 11/11/2017
RIP: 0010:__writeback_inodes_sb_nr+0xb8/0xd0
Code: 0f b6 d1 48 8d 74 24 10 e8 35 fc ff ff 48 89 e7 e8 7d fb ff ff 48 8b 44 24 48 65 48 2b 04 25 28 00 00 00 75 09 48 83 c4 50 c3 <0f> 0b eb cf e8 df 8c 75 00 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f
RSP: 0018:ffffb1f5448f7d98 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff961185aa5488 RCX: 0000000000000000
RDX: 0000000000000002 RSI: 0000000000004b45 RDI: ffff9611b7220000
RBP: ffff9611b64d3958 R08: ffff961184efc800 R09: 0000000000000140
R10: ffff9611859e6400 R11: ffff961192af3c10 R12: ffff9611838f7c00
R13: ffff961185aa5000 R14: ffff961185aa5460 R15: 0000000000011a0f
FS:  0000000000000000(0000) GS:ffff9611fad00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f654bc76b58 CR3: 0000000002c60000 CR4: 00000000003506e0
Call Trace:
  btrfs_commit_transaction+0x448/0xbc0 [btrfs]
  ? start_transaction+0xcc/0x5b0 [btrfs]
  transaction_kthread+0x143/0x170 [btrfs]
  ? btrfs_cleanup_transaction.isra.0+0x560/0x560 [btrfs]
  kthread+0x133/0x150
  ? __kthread_bind_mask+0x60/0x60
  ret_from_fork+0x22/0x30
---[ end trace 3cefecf5d9d20b50 ]---

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WARNING: CPU: 0 PID: 758 at fs/fs-writeback.c:2472 __writeback_inodes_sb_nr+0xb8/0xd0

That bug was introduced in 4.15 as part of a fix for a deadlock bug.
It's still there today.  Not very high on anyone's TODO list as it's
mostly harmless--btrfs can't be umounted during a transaction as the
umount itself uses a transaction.  The warning doesn't come from btrfs
code, so we can't just turn it off.

That warning spams my logs every 1-5 minutes. There is no unmounting 
happening.

quoted

Modules linked in: iTCO_wdt wireguard curve25519_x86_64 libchacha20poly1305 intel_pmc_bxt iTCO_vendor_support chacha_x86_64 poly1305_x86_64 libblake2s blake2s_x86_>
CPU: 0 PID: 758 Comm: journal-offline Tainted: G        W         5.10.26-1-MANJARO #1
Hardware name: Hetzner vServer, BIOS 20171111 11/11/2017
RIP: 0010:__writeback_inodes_sb_nr+0xb8/0xd0
Code: 0f b6 d1 48 8d 74 24 10 e8 35 fc ff ff 48 89 e7 e8 7d fb ff ff 48 8b 44 24 48 65 48 2b 04 25 28 00 00 00 75 09 48 83 c4 50 c3 <0f> 0b eb cf e8 df 8c 75 00 66>
RSP: 0018:ffffb1f540d7fd40 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff961185aa5488 RCX: 0000000000000000
RDX: 0000000000000002 RSI: 0000000000004be5 RDI: ffff9611b7220000
RBP: ffff961182209208 R08: ffff961184efc800 R09: 0000000000000140
R10: ffff9611859e6400 R11: ffff961192af3c10 R12: ffff961183891200
R13: ffff961185aa5000 R14: ffff961185aa5460 R15: ffff9611b65d5e10
FS:  00007f654b80e640(0000) GS:ffff9611fac00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f654cf39010 CR3: 0000000003884000 CR4: 00000000003506f0
Call Trace:
  btrfs_commit_transaction+0x448/0xbc0 [btrfs]
  ? btrfs_wait_ordered_range+0x1b8/0x210 [btrfs]
  ? btrfs_sync_file+0x2b8/0x4e0 [btrfs]
  btrfs_sync_file+0x343/0x4e0 [btrfs]
  __x64_sys_fsync+0x34/0x60
  do_syscall_64+0x33/0x40

Normally you need to mount -o flushoncommit to trigger this warning.
Maybe sync is triggering it too?

I've looked again and yes, this "special" filesystem is mounted 
flushoncommit and discard=async. Would it be better to not set these 
options, for now?

BR