zbd/009 (btrfs on zone gaps) fail on current Linus tree

[Christoph Hellwig <hch@infradead.org>]

At least in my usual x86_64 test VM:

zbd/009 (test gap zone support with BTRFS)                  
[   21.102324] run blktests zbd/009 at 2025-10-07 06:10:44
[   21.251500] sd 3:0:0:0: [sda] Synchronizing SCSI cache
[   21.413634] scsi_debug:sdebug_driver_probe: scsi_debug: trim poll_queues to 0. poll_q/nr_hw )
[   21.414056] scsi host3: scsi_debug: version 0191 [20210520]
[   21.414056]   dev_size_mb=1024, opts=0x0, submit_queues=1, statistics=0
[   21.415307] scsi 3:0:0:0: Direct-Access-ZBC Linux    scsi_debug 0191 PQ: 0 ANSI: 7
[   21.416384] scsi 3:0:0:0: Power-on or device reset occurred
[   21.416981] sd 3:0:0:0: Attached scsi generic sg1 type 20
[   21.417533] sd 3:0:0:0: [sda] Host-managed zoned block device
[   21.418153] sd 3:0:0:0: [sda] 262144 4096-byte logical blocks: (1.07 GB/1.00 GiB)
[   21.418676] sd 3:0:0:0: [sda] Write Protect is off
[   21.419017] sd 3:0:0:0: [sda] Write cache: enabled, read cache: enabled, supports DPO and FUA
[   21.419685] sd 3:0:0:0: [sda] permanent stream count = 5
[   21.420158] sd 3:0:0:0: [sda] Preferred minimum I/O size 4096 bytes
[   21.420593] sd 3:0:0:0: [sda] Optimal transfer size 4194304 bytes
[   21.421261] sd 3:0:0:0: [sda] 256 zones of 1024 logical blocks
[   21.456700] sd 3:0:0:0: [sda] Attached SCSI disk
[   21.523845] BTRFS: device fsid 9bcd6f4c-db2e-44d7-8597-4eb5774c1460 devid 1 transid 6 /dev/s)
[   21.528211] BTRFS info (device sda): first mount of filesystem 9bcd6f4c-db2e-44d7-8597-4eb570
[   21.528623] BTRFS info (device sda): using crc32c (crc32c-lib) checksum algorithm
[   21.530206] BTRFS info (device sda): host-managed zoned block device /dev/sda, 256 zones of s
[   21.530663] BTRFS info (device sda): zoned mode enabled with zone size 4194304
[   21.532601] BTRFS info (device sda): checking UUID tree
[   21.532909] BTRFS info (device sda): enabling ssd optimizations
[   21.533145] BTRFS info (device sda): enabling free space tree

[  242.795457] INFO: task kworker/u8:4:859 blocked for more than 120 seconds.
[  242.796028]       Tainted: G                 N  6.17.0+ #4047
[  242.796426] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  242.796941] task:kworker/u8:4    state:D stack:0     pid:859 tgid:859   ppid:2      task_f0
[  242.797667] Workqueue: writeback wb_workfn (flush-btrfs-2)
[  242.798065] Call Trace:
[  242.798227]  <TASK>
[  242.798369]  __schedule+0x524/0xb60
[  242.798601]  schedule+0x29/0xe0
[  242.798804]  io_schedule+0x4b/0x70
[  242.799024]  folio_wait_bit_common+0x126/0x390
[  242.799300]  ? filemap_get_folios_tag+0x247/0x2a0
[  242.800054]  ? __pfx_wake_page_function+0x10/0x10
[  242.800354]  extent_write_cache_pages+0x5c6/0x9c0
[  242.800631]  ? stack_depot_save_flags+0x29/0x870
[  242.800904]  ? set_track_prepare+0x45/0x70
[  242.801145]  ? __kmalloc_noprof+0x3a7/0x4e0
[  242.801391]  ? virtqueue_add_sgs+0x308/0x720
[  242.801644]  ? virtblk_add_req+0x81/0xe0
[  242.801875]  ? virtblk_add_req_batch+0x4b/0x100
[  242.802140]  ? virtio_queue_rqs+0x133/0x180
[  242.802385]  ? blk_mq_dispatch_queue_requests+0x155/0x180
[  242.802697]  ? blk_mq_flush_plug_list+0x73/0x160
[  242.802967]  ? preempt_count_add+0x4d/0xb0
[  242.803210]  btrfs_writepages+0x70/0x120
[  242.803636]  do_writepages+0xc5/0x160
[  242.803870]  __writeback_single_inode+0x3c/0x330
[  242.804154]  writeback_sb_inodes+0x21a/0x4d0
[  242.804436]  __writeback_inodes_wb+0x47/0xe0
[  242.804758]  wb_writeback+0x19a/0x310
[  242.805029]  wb_workfn+0x348/0x440
[  242.805248]  process_one_work+0x169/0x320
[  242.805487]  worker_thread+0x246/0x390
[  242.805711]  ? _raw_spin_unlock_irqrestore+0x1d/0x40
[  242.806003]  ? __pfx_worker_thread+0x10/0x10
[  242.806253]  kthread+0x106/0x220
[  242.806454]  ? __pfx_kthread+0x10/0x10
[  242.806683]  ? __pfx_kthread+0x10/0x10
[  242.806915]  ret_from_fork+0x11d/0x160
[  242.807145]  ? __pfx_kthread+0x10/0x10
[  242.807646]  ret_from_fork_asm+0x1a/0x30
[  242.807904]  </TASK>