Re: BTRFS discard crash: failed to run delayed ref for logical 15506102321152 num_bytes 16384 type 182 action 2 ref_mod 1: -2 6.11.2)

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2026/4/11 13:05, Marc MERLIN 写道:
> [Is there a more appropriate way to report FS corruption? Looks like
> Emails to just linux-btrfs@vger.kernel.org do not get seen amongst all
> the patches hiding a normal Email]
> 
> Howdy,
> 
> I had btfrs filesystem on top of raid5 with 5 spinning drives.
> I mistakenly enabled discard by mistake which caused a crash when the discard thread tried
> to run (no discard on those drives)
> Kernel 6.12
> 
> I worked on recovery using gemini 3.0 pro, mounting read only is fine, but I need read write
> or will waste days (probably weeks) recreating this entire 20TB+ backup over the internet
> 
> I'm not qualified to say if everything Gemini said was correct, but I think summary is:
> 1) discard can apparently kill a filesystem when it's hard drives below (it did for me)
> 2) -o skip_balance,usebackuproot didn't help
> 3) no way to mount after space cache has been cleared and block-group-tree is enabled
> 4) still no way to mount read write after removing block-group-tree
> 
> It started with:
> [23345.326321] BTRFS: error (device dm-0 state A) in do_free_extent_accounting:2996: errno=-2 No such entry
> [23345.336394] BTRFS error (device dm-0 state EA): failed to run delayed ref for logical 15506102321152 num_bytes 16384 type 182 action 2 ref_mod 1: -2
> [23345.350299] BTRFS: error (device dm-0 state EA) in btrfs_run_delayed_refs:2215: errno=-2 No such entry
> [23345.360154] BTRFS warning (device dm-0 state EA):
> 
> I ended up with:
> 
> moremagic:~# mount -t btrfs -o rw,skip_balance,space_cache=v2,clear_cache /dev/mapper/crypt_bcache0 /mnt/btrfs_bigbackup
> BTRFS: device label DS6 devid 1 transid 296950 /dev/mapper/crypt_bcache0 (251:0) scanned by mount (6029)
> BTRFS info (device dm-0): first mount of filesystem a97dec85-a0d5-42ab-a0ef-e9b7479fbe43
> BTRFS info (device dm-0): using crc32c (crc32c-generic) checksum algorithm
> BTRFS warning (device dm-0): read-write for sector size 4096 with page size 16384 is experimental
> BTRFS info (device dm-0): bdev /dev/mapper/crypt_bcache0 errs: wr 0, rd 0, flush 0, corrupt 5074, gen 0
> ------------[ cut here ]------------
> BTRFS: Transaction aborted (error -2)
> WARNING: CPU: 3 PID: 6029 at fs/btrfs/extent-tree.c:2996 __btrfs_free_extent.isra.0+0x13a0/0x14a0 [btrfs]
> Modules linked in: dm_crypt dm_mod bcache raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xt_MASQUERADE ipt_REJECT nf_reject_ipv4 xt_tcpudp xt_conntrack xt_LOG nf_log_syslog nft_compat nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables rfcomm algif_hash algif_skcipher af_alg bnep cp210x brcmfmac_wcc binfmt_misc usbserial hci_uart brcmfmac btbcm vc4 snd_soc_hdmi_codec brcmutil bluetooth drm_display_helper cfg80211 cec drm_dma_helper rpi_hevc_dec ecdh_generic v4l2_mem2mem ecc snd_soc_core pisp_be videobuf2_dma_contig v3d videobuf2_memops videobuf2_v4l2 gpu_sched rfkill videodev drm_shmem_helper snd_compress snd_pcm_dmaengine snd_pcm videobuf2_common rp1_pio snd_timer snd drm_kms_helper mc raspberrypi_gpiomem rp1_fw sg sch_fq_codel ecryptfs fuse drm drm_panel_orientation_quirks backlight nfnetlink ip_tables x_tables raid1 aes_ce_blk aes_ce_cipher ghash_ce gf128mul libaes sha2_ce spidev sha256_arm64 sha1_ce raspberrypi_hwmon sha1_generic ahci i2c_brcmstb spi_bcm2835
>   md_mod gpio_keys libahci pwm_fan rp1_adc libata rp1_mailbox nvmem_rmem uio_pdrv_genirq uio btrfs blake2b_generic xor xor_neon raid6_pq zram lz4_compress ipv6
> CPU: 3 UID: 0 PID: 6029 Comm: mount Not tainted 6.12.47+rpt-rpi-2712 #1  Debian 1:6.12.47-1+rpt1
> Hardware name: Raspberry Pi 5 Model B Rev 1.1 (DT)
> pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : __btrfs_free_extent.isra.0+0x13a0/0x14a0 [btrfs]
> lr : __btrfs_free_extent.isra.0+0x13a0/0x14a0 [btrfs]
> sp : ffffc000868bb680
> x29: ffffc000868bb720 x28: 0000000000000000 x27: 0000000000002f02
> x26: 000000000000007f x25: ffff8001de833aa0 x24: 0000000000004000
> x23: 0000000000000000 x22: ffff800102b64e70 x21: 0000000000004000
> x20: 00000e1a4bb88000 x19: 00000000fffffffe x18: 0000000000000000
> x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
> x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
> x11: 00000000000000c0 x10: 0000000000001a40 x9 : ffffd06fce4e06c0
> x8 : ffff80011f56e0a0 x7 : 000000042f72a7bd x6 : 0000000000000039
> x5 : 0000000000000001 x4 : 0000000000001ab0 x3 : 0000000000000804
> x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff80011f56c600
> Call trace:
>   __btrfs_free_extent.isra.0+0x13a0/0x14a0 [btrfs]
>   __btrfs_run_delayed_refs+0x508/0xec0 [btrfs]
>   btrfs_run_delayed_refs+0x48/0x198 [btrfs]
>   btrfs_commit_transaction+0x88/0xe20 [btrfs]
>   btrfs_recover_relocation+0x55c/0x5d0 [btrfs]
>   btrfs_start_pre_rw_mount+0x1d4/0x470 [btrfs]
>   open_ctree+0x101c/0x13b8 [btrfs]
>   btrfs_get_tree+0x5b4/0x800 [btrfs]
>   vfs_get_tree+0x30/0x108
>   fc_mount+0x20/0x68
>   btrfs_get_tree+0x238/0x800 [btrfs]
>   vfs_get_tree+0x30/0x108
>   vfs_cmd_create+0x58/0xf8
>   __arm64_sys_fsconfig+0x444/0x5b8
>   invoke_syscall+0x50/0x120
>   el0_svc_common.constprop.0+0x48/0xf0
>   do_el0_svc+0x24/0x38
>   el0_svc+0x30/0xf8
>   el0t_64_sync_handler+0x120/0x130
>   el0t_64_sync+0x190/0x198
> ---[ end trace 0000000000000000 ]---
> BTRFS: error (device dm-0 state A) in do_free_extent_accounting:2996: errno=-2 No such entry
> BTRFS error (device dm-0 state EA): failed to run delayed ref for logical 15506102321152 num_bytes 16384 type 182 action 2 ref_mod 1: -2

There is a missing extent item for a shared tree block, aka extent tree 
corruption.

Please try skip_balance to see if the fs can be mounted, then cancel the 
relocation.

Then re-run btrfs check so we do not have balance complicating the 
situation.

> BTRFS: error (device dm-0 state EA) in btrfs_run_delayed_refs:2215: errno=-2 No such entry
> BTRFS warning (device dm-0 state EA): failed to recover relocation: -2
> BTRFS error (device dm-0 state EA): commit super ret -30
> BTRFS error (device dm-0 state EA): open_ctree failed: -2
> 
> 
> Gemini said

Please drop whatever LLM says, for most cases it makes no difference nor 
sense.

I even believe it's making things worse.

> 
> more details:
> backuproot didn't work (read write)
> I was forced to run
> btrfstune --convert-from-block-group-tree /dev/mapper/crypt_bcache0

Please do not do whatever writes to the fs until you know why you should 
do that.
And in this case, this will only make things worse.

Now I do not even know if this is the original problem or something 
introduced by your writes.


At least btrfs-progs can add some checks to prevent such operations when 
there is a running balance.
I believe that's the only thing we can benefit from your report.

Next time, please do not do whatever crazy/stupid things unless *YOU* 
know the reason.

Thanks,
Qu

> because
> When you ran btrfs check --clear-space-cache v2, the tool did exactly
> what it was supposed to do: it deleted the Free Space Tree and removed
> the FREE_SPACE_TREE flag from your superblock.
> The Conflict: Your 23TB array was formatted with the modern
> block-group-tree feature (which speeds up mounting).
> The Kernel Rule: The Btrfs kernel code explicitly dictates: If the Block
> Group Tree is enabled, the Free Space Tree MUST also be enabled. * The
> Crash: Because the FREE_SPACE_TREE flag is now missing, the kernel sees
> an "illegal" superblock state and throws a fatal -22 error, refusing to
> proceed to the mount options.
> 
> This was vexing, hours lost removing the block group tree.
> and when it was finally finished,
> mount -t btrfs -o skip_balance /dev/mapper/crypt_bcache0 /mnt/btrfs_bigbackup/
> did run, but crashed as above
> 
> Now doing a repair in case it can salvage things.
> 
> Marc