Re: [syzbot] [btrfs?] INFO: task hung in __alloc_workqueue (2)

[Qu Wenruo <wqu@suse.com>]

在 2025/8/11 07:25, syzbot 写道:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    479058002c32 Merge tag 'ata-6.17-rc1-fixes' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1315e042580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=943d6f7b1ddd8799
> dashboard link: https://syzkaller.appspot.com/bug?extid=ead9101689c4ca30dbe8
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11d262f0580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/7226b9adab95/disk-47905800.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b10c6c12e41f/vmlinux-47905800.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7e99b92d1763/bzImage-47905800.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/1ca3e7130df3/mount_0.gz
>    fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=17f2f6a2580000)
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ead9101689c4ca30dbe8@syzkaller.appspotmail.com
> 
> INFO: task syz.1.170:8358 blocked for more than 143 seconds.
>        Tainted: G        W           6.16.0-syzkaller-11852-g479058002c32 #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz.1.170       state:D stack:26024 pid:8358  tgid:8358  ppid:6003   task_flags:0x400140 flags:0x00004006
> Call Trace:
>   <TASK>
>   context_switch kernel/sched/core.c:5357 [inline]
>   __schedule+0x16f3/0x4c20 kernel/sched/core.c:6961
>   __schedule_loop kernel/sched/core.c:7043 [inline]
>   schedule+0x165/0x360 kernel/sched/core.c:7058
>   schedule_timeout+0x9a/0x270 kernel/time/sleep_timeout.c:75
>   do_wait_for_common kernel/sched/completion.c:100 [inline]
>   __wait_for_common kernel/sched/completion.c:121 [inline]
>   wait_for_common kernel/sched/completion.c:132 [inline]
>   wait_for_completion+0x2bf/0x5d0 kernel/sched/completion.c:153
>   kthread_flush_worker+0x1c6/0x240 kernel/kthread.c:1563

This is flushing pwq_release_worker during error handling, and I didn't 
see anything btrfs specific except btrfs is allocating an ordered 
workqueue which utilizes WQ_UNBOUND flag.

And that WQ_UNBOUND flag is pretty widely used among other filesystems, 
maybe it's just btrfs have too many workqueues triggering this?

Adding workqueue maintainers.

Thanks,
Qu

>   __alloc_workqueue+0x146b/0x1b70 kernel/workqueue.c:5763
>   alloc_workqueue_noprof+0xd4/0x210 kernel/workqueue.c:5786
>   btrfs_init_workqueues+0x42c/0x6c0 fs/btrfs/disk-io.c:2000
>   open_ctree+0x11ef/0x3a10 fs/btrfs/disk-io.c:3424
>   btrfs_fill_super fs/btrfs/super.c:977 [inline]
>   btrfs_get_tree_super fs/btrfs/super.c:1937 [inline]
>   btrfs_get_tree_subvol fs/btrfs/super.c:2074 [inline]
>   btrfs_get_tree+0xf55/0x1820 fs/btrfs/super.c:2108
>   vfs_get_tree+0x92/0x2b0 fs/super.c:1815
>   do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805
>   do_mount fs/namespace.c:4133 [inline]
>   __do_sys_mount fs/namespace.c:4344 [inline]
>   __se_sys_mount+0x317/0x410 fs/namespace.c:4321
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fb27169038a
> RSP: 002b:00007ffefe6fdaf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007ffefe6fdb80 RCX: 00007fb27169038a
> RDX: 00002000000055c0 RSI: 0000200000000200 RDI: 00007ffefe6fdb40
> RBP: 00002000000055c0 R08: 00007ffefe6fdb80 R09: 000000000300000a
> R10: 000000000300000a R11: 0000000000000246 R12: 0000200000000200
> R13: 00007ffefe6fdb40 R14: 00000000000055a3 R15: 0000200000000080
>   </TASK>
> 
> Showing all locks held in the system:
> 1 lock held by khungtaskd/38:
>   #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
>   #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
>   #0: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
> 1 lock held by udevd/5207:
>   #0: ffff8880358bfa18 (&ep->lock){++++}-{3:3}, at: write_lock_irq include/linux/rwlock_rt.h:104 [inline]
>   #0: ffff8880358bfa18 (&ep->lock){++++}-{3:3}, at: ep_poll fs/eventpoll.c:2127 [inline]
>   #0: ffff8880358bfa18 (&ep->lock){++++}-{3:3}, at: do_epoll_wait+0x84d/0xbb0 fs/eventpoll.c:2560
> 2 locks held by getty/5598:
>   #0: ffff88823bfae8a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
>   #1: ffffc90003e8b2e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x444/0x1410 drivers/tty/n_tty.c:2222
> 3 locks held by kworker/u8:3/5911:
> 3 locks held by kworker/u8:7/5942:
> 6 locks held by udevd/6060:
> 1 lock held by udevd/6069:
> 1 lock held by udevd/6190:
> 6 locks held by udevd/6237:
>   #0: ffff88802205eea8 (&sb->s_type->i_mutex_key#7){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:884 [inline]
>   #0: ffff88802205eea8 (&sb->s_type->i_mutex_key#7){++++}-{4:4}, at: blkdev_read_iter+0x2ff/0x440 block/fops.c:848
>   #1: ffff88803b280250 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:472 [inline]
>   #1: ffff88803b280250 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:277 [inline]
>   #1: ffff88803b280250 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x32/0x300 mm/mmap_lock.c:337
>   #2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
>   #2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
>   #2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: ___pte_offset_map+0x29/0x200 mm/pgtable-generic.c:286
>   #3: ffff888026394c58 (ptlock_ptr(ptdesc)#2){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
>   #3: ffff888026394c58 (ptlock_ptr(ptdesc)#2){+.+.}-{3:3}, at: __pte_offset_map_lock+0x13e/0x210 mm/pgtable-generic.c:401
>   #4: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
>   #4: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
>   #4: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
>   #4: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57
>   #5: ffff8880b8833490 ((lock)#2){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
>   #5: ffff8880b8833490 ((lock)#2){+.+.}-{3:3}, at: __folio_batch_add_and_move+0x170/0x540 mm/swap.c:-1
> 2 locks held by kworker/u8:9/6857:
> 1 lock held by syz.1.170/8358:
>   #0: ffff88802315a0d0 (&type->s_umount_key#53/1){+.+.}-{4:4}, at: alloc_super+0x204/0x990 fs/super.c:345
> 4 locks held by kworker/u8:11/10100:
> 1 lock held by syz.3.381/11502:
> 2 locks held by syz.4.382/11516:
>   #0: ffff88805e1a80d0 (&type->s_umount_key#53/1){+.+.}-{4:4}, at: alloc_super+0x204/0x990 fs/super.c:345
>   #1: ffffffff8d611078 (bit_wait_table + i){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
>   #1: ffffffff8d611078 (bit_wait_table + i){+.+.}-{3:3}, at: finish_wait kernel/sched/wait.c:394 [inline]
>   #1: ffffffff8d611078 (bit_wait_table + i){+.+.}-{3:3}, at: __wait_on_bit+0x1ff/0x300 kernel/sched/wait_bit.c:55
> 3 locks held by syz.0.383/11517:
>   #0: ffff88801aa94488 (sb_writers#5){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:3107 [inline]
>   #0: ffff88801aa94488 (sb_writers#5){.+.+}-{0:0}, at: vfs_write+0x217/0xaa0 fs/read_write.c:682
>   #1: ffff888054b3c598 (&sb->s_type->i_mutex_key#12){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
>   #1: ffff888054b3c598 (&sb->s_type->i_mutex_key#12){+.+.}-{4:4}, at: shmem_file_write_iter+0x82/0x120 mm/shmem.c:3518
>   #2: ffff8880b8833490 ((lock)#2){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
>   #2: ffff8880b8833490 ((lock)#2){+.+.}-{3:3}, at: __folio_batch_add_and_move+0x170/0x540 mm/swap.c:-1
> 3 locks held by syz.5.384/11518:
>   #0: ffff88801aa94488 (sb_writers#5){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:3107 [inline]
>   #0: ffff88801aa94488 (sb_writers#5){.+.+}-{0:0}, at: vfs_write+0x217/0xaa0 fs/read_write.c:682
>   #1: ffff8880254a6e88 (&sb->s_type->i_mutex_key#12){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:869 [inline]
>   #1: ffff8880254a6e88 (&sb->s_type->i_mutex_key#12){+.+.}-{4:4}, at: shmem_file_write_iter+0x82/0x120 mm/shmem.c:3518
>   #2: ffff8880b8833490 ((lock)#2){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
>   #2: ffff8880b8833490 ((lock)#2){+.+.}-{3:3}, at: __folio_batch_add_and_move+0x170/0x540 mm/swap.c:-1
> 7 locks held by syz.2.385/11535:
> 1 lock held by udevadm/11536:
> 
> =============================================
> 
> NMI backtrace for cpu 1
> CPU: 1 UID: 0 PID: 38 Comm: khungtaskd Tainted: G        W           6.16.0-syzkaller-11852-g479058002c32 #0 PREEMPT_{RT,(full)}
> Tainted: [W]=WARN
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
> Call Trace:
>   <TASK>
>   dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>   nmi_cpu_backtrace+0x39e/0x3d0 lib/nmi_backtrace.c:113
>   nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
>   trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
>   check_hung_uninterruptible_tasks kernel/hung_task.c:328 [inline]
>   watchdog+0xf93/0xfe0 kernel/hung_task.c:491
>   kthread+0x711/0x8a0 kernel/kthread.c:463
>   ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
>   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>   </TASK>
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0
> CPU: 0 UID: 0 PID: 5911 Comm: kworker/u8:3 Tainted: G        W           6.16.0-syzkaller-11852-g479058002c32 #0 PREEMPT_{RT,(full)}
> Tainted: [W]=WARN
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
> Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet
> RIP: 0010:get_timer_this_cpu_base kernel/time/timer.c:939 [inline]
> RIP: 0010:__mod_timer+0x81c/0xf60 kernel/time/timer.c:1101
> Code: 01 00 00 00 48 8b 5c 24 20 41 0f b6 44 2d 00 84 c0 0f 85 72 06 00 00 8b 2b e8 f0 bb 49 09 41 89 c5 89 c3 bf 08 00 00 00 89 c6 <e8> 0f c1 12 00 41 83 fd 07 44 89 34 24 0f 87 69 06 00 00 e8 4c bc
> RSP: 0018:ffffc90004fff680 EFLAGS: 00000082
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: f9fab87ca5ec6a00
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000008
> RBP: 0000000000200000 R08: 0000000000000000 R09: 0000000000000000
> R10: dffffc0000000000 R11: fffff520009ffeac R12: ffff8880b8825a80
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000802
> FS:  0000000000000000(0000) GS:ffff8881268cd000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f46b6524000 CR3: 000000003afb2000 CR4: 00000000003526f0
> Call Trace:
>   <TASK>
>   queue_delayed_work_on+0x18b/0x280 kernel/workqueue.c:2559
>   queue_delayed_work include/linux/workqueue.h:684 [inline]
>   batadv_forw_packet_queue+0x239/0x2a0 net/batman-adv/send.c:691
>   batadv_iv_ogm_schedule_buff net/batman-adv/bat_iv_ogm.c:842 [inline]
>   batadv_iv_ogm_schedule+0x892/0xf00 net/batman-adv/bat_iv_ogm.c:874
>   batadv_iv_send_outstanding_bat_ogm_packet+0x6c6/0x7e0 net/batman-adv/bat_iv_ogm.c:1714
>   process_one_work kernel/workqueue.c:3236 [inline]
>   process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
>   worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
>   kthread+0x711/0x8a0 kernel/kthread.c:463
>   ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
>   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>   </TASK>
> 
> 
> ---
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