Re: error in btrfs_create_pending_block_groups:2788: errno=-17 Object already exists

[Boris Burkov <boris@bur.io>]

On Thu, Jan 08, 2026 at 03:53:17PM +0100, Dimitrios Apostolou wrote:
> Hello list,
> 
> I got an error while copying recursively (cp -a) several TBs of GB-sized
> files, from an old zstd:3 compressed btrfs filesystem, to a newly created
> same-settings (zstd:3 compressed) btrfs filesystem. Error happened after
> many hours of copying, without any issues or log messages before that. No
> hardware errors were logged either.
> 
> OS: Ubuntu 24.04 with HWE kernel 6.14.0-37-generic.
> 
> The kernel source code should be about this one here:
> https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble/tree/fs/btrfs/block-group.c?h=hwe-6.14-next#n2788
> 
> 
> Mkfs output:
> 
> # mkfs.btrfs /dev/sde
> btrfs-progs v6.6.3
> See https://btrfs.readthedocs.io for more information.
> 
> Performing full device TRIM /dev/sde (10.00TiB) ...
> NOTE: several default settings have changed in version 5.15, please make
> sure
>       this does not affect your deployments:
>       - DUP for metadata (-m dup)
>       - enabled no-holes (-O no-holes)
>       - enabled free-space-tree (-R free-space-tree)
> 
> Label:              (null)
> UUID:               ff746273-9a0d-419c-9cc0-efe1c85b5857
> Node size:          16384
> Sector size:        4096
> Filesystem size:    10.00TiB
> Block group profiles:
>   Data:             single            8.00MiB
>   Metadata:         DUP               1.00GiB
>   System:           DUP               8.00MiB
> SSD detected:       yes
> Zoned device:       no
> Incompat features:  extref, skinny-metadata, no-holes, free-space-tree
> Runtime features:   free-space-tree
> Checksum:           crc32c
> Number of devices:  1
> Devices:
>    ID        SIZE  PATH
>     1    10.00TiB  /dev/sde
> 
> 
> Kernel stacktrace:
> 
> [Jan 7 21:02] ------------[ cut here ]------------
> [  +0.000005] BTRFS: Transaction aborted (error -17)
> [  +0.000039] WARNING: CPU: 9 PID: 5589 at fs/btrfs/block-group.c:2788 btrfs_create_pending_block_groups+0x525/0x5a0 [btrfs]
> [  +0.000071] Modules linked in: tls udp_diag tcp_diag inet_diag qrtr vsock_loopback vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vsock cfg80211 binfmt_misc intel_rapl_msr intel_rapl_common intel_uncore_frequency_common isst_if_common skx_edac_common nfit rapl vmw_balloon vmwgfx i2c_piix>
> [  +0.000036] CPU: 9 UID: 0 PID: 5589 Comm: btrfs-transacti Not tainted 6.14.0-37-generic #37~24.04.1-Ubuntu
> [  +0.000003] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020
> [  +0.000002] RIP: 0010:btrfs_create_pending_block_groups+0x525/0x5a0 [btrfs]
> [  +0.000049] Code: 48 8b 7d 98 e8 ac 9a f6 ff e9 45 fd ff ff 4c 89 ef e8 7f 23 3a f9 e9 ff fc ff ff 44 89 e6 48 c7 c7 d8 07 67 c0 e8 7b 19 ff f8 <0f> 0b e9 5e fe ff ff 44 89 e6 48 c7 c7 d8 07 67 c0 e8 65 19 ff f8
> [  +0.000001] RSP: 0018:ffffcf0b0469fd58 EFLAGS: 00010246
> [  +0.000002] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
> [  +0.000002] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> [  +0.000000] RBP: ffffcf0b0469fde8 R08: 0000000000000000 R09: 0000000000000000
> [  +0.000001] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000ffffffef
> [  +0.000001] R13: ffff8a86290e2840 R14: ffff8a8bb2f8c118 R15: ffff8a82c07cf2a0
> [  +0.000001] FS:  0000000000000000(0000) GS:ffff8a91bfa80000(0000) knlGS:0000000000000000
> [  +0.000001] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  +0.000001] CR2: 000074cdbd8053e8 CR3: 0000000caf7c0003 CR4: 0000000000770ef0
> [  +0.000025] PKRU: 55555554
> [  +0.000002] Call Trace:
> [  +0.000001]  <TASK>
> [  +0.000003]  btrfs_commit_transaction+0x7d/0xc50 [btrfs]
> [  +0.000051]  ? hrtimers_cpu_dying+0x130/0x1f0
> [  +0.000004]  transaction_kthread+0x167/0x1d0 [btrfs]
> [  +0.000042]  ? __pfx_transaction_kthread+0x10/0x10 [btrfs]
> [  +0.000038]  kthread+0xfb/0x230
> [  +0.000003]  ? __pfx_kthread+0x10/0x10
> [  +0.000002]  ret_from_fork+0x47/0x70
> [  +0.000003]  ? __pfx_kthread+0x10/0x10
> [  +0.000001]  ret_from_fork_asm+0x1a/0x30
> [  +0.000004]  </TASK>
> [  +0.000001] ---[ end trace 0000000000000000 ]---
> [  +0.000002] BTRFS: error (device sde state A) in btrfs_create_pending_block_groups:2788: errno=-17 Object already exists
> [  +0.000014] BTRFS info (device sde state EA): forced readonly
> [  +0.000603] BTRFS warning (device sde state EA): Skipping commit of aborted transaction.
> 
> 
> 
> Any ideas?

Not yet, but I have seen it at Meta as well and am investigating.

Are you able to reproduce it or did it happen just once?

Hopefully something for you soon.

> 
> Thank you in advance,
> Dimitris
> 

Thanks,
Boris