Forwarded: Re: [syzbot] [net] [virt] INFO: task hung in __vhost_worker_flush

[syzbot <syzbot+7f3bbe59e8dd2328a990@syzkaller.appspotmail.com>]

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Subject: Re: [syzbot] [net] [virt] INFO: task hung in __vhost_worker_flush
Author: mst@redhat.com

On Sat, Aug 30, 2025 at 07:21:32PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    11e7861d680c Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17c5c242580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a
> dashboard link: https://syzkaller.appspot.com/bug?extid=7f3bbe59e8dd2328a990
> compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1671ba62580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1685aa62580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/aa8c34462d5d/disk-11e7861d.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f90079573556/vmlinux-11e7861d.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/8571495e4fea/bzImage-11e7861d.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+7f3bbe59e8dd2328a990@syzkaller.appspotmail.com
> 
> INFO: task syz.0.17:6038 blocked for more than 143 seconds.
>       Not tainted syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:syz.0.17        state:D stack:27224 pid:6038  tgid:6038  ppid:5979   task_flags:0x400040 flags:0x00004004
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:5357 [inline]
>  __schedule+0x1190/0x5de0 kernel/sched/core.c:6961
>  __schedule_loop kernel/sched/core.c:7043 [inline]
>  schedule+0xe7/0x3a0 kernel/sched/core.c:7058
>  schedule_timeout+0x257/0x290 kernel/time/sleep_timeout.c:75
>  do_wait_for_common kernel/sched/completion.c:100 [inline]
>  __wait_for_common+0x2fc/0x4e0 kernel/sched/completion.c:121
>  __vhost_worker_flush+0x1a8/0x1d0 drivers/vhost/vhost.c:296
>  vhost_worker_flush drivers/vhost/vhost.c:303 [inline]
>  vhost_dev_flush+0xac/0x110 drivers/vhost/vhost.c:313
>  vhost_vsock_flush drivers/vhost/vsock.c:698 [inline]
>  vhost_vsock_dev_release+0x19f/0x400 drivers/vhost/vsock.c:750
>  __fput+0x402/0xb70 fs/file_table.c:468
>  task_work_run+0x14d/0x240 kernel/task_work.c:227
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43
>  exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
>  syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
>  syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
>  do_syscall_64+0x3f6/0x4c0 arch/x86/entry/syscall_64.c:100
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f1fdc78ebe9
> RSP: 002b:00007ffcf43dcf28 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
> RAX: 0000000000000000 RBX: 00007f1fdc9c7da0 RCX: 00007f1fdc78ebe9
> RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
> RBP: 00007f1fdc9c7da0 R08: 0000000000000000 R09: 00000008f43dd21f
> R10: 00007f1fdc9c7cb0 R11: 0000000000000246 R12: 00000000000248b9
> R13: 00007ffcf43dd020 R14: ffffffffffffffff R15: 00007ffcf43dd040
>  </TASK>
> 
> Showing all locks held in the system:
> 1 lock held by khungtaskd/31:
>  #0: ffffffff8e5c1220 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
>  #0: ffffffff8e5c1220 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
>  #0: ffffffff8e5c1220 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x36/0x1c0 kernel/locking/lockdep.c:6775
> 3 locks held by kworker/u9:1/5174:
>  #0: ffff8880605ef148 ((wq_completion)hci2){+.+.}-{0:0}, at: process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3211
>  #1: ffffc9000f89fd10 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3212
>  #2: ffff8880256d4dc0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_cmd_sync_work+0x175/0x430 net/bluetooth/hci_sync.c:331
> 2 locks held by getty/5615:
>  #0: ffff88814d35e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
>  #1: ffffc9000332b2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x41b/0x14f0 drivers/tty/n_tty.c:2222
> 
> =============================================
> 
> NMI backtrace for cpu 0
> CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
>  nmi_cpu_backtrace+0x27b/0x390 lib/nmi_backtrace.c:113
>  nmi_trigger_cpumask_backtrace+0x29c/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+0xf0e/0x1260 kernel/hung_task.c:491
>  kthread+0x3c5/0x780 kernel/kthread.c:463
>  ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>
> Sending NMI from CPU 0 to CPUs 1:
> NMI backtrace for cpu 1
> CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
> RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:82
> Code: 0c 62 02 c3 cc cc cc cc 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d d3 12 16 00 fb f4 <e9> 4c 09 03 00 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
> RSP: 0018:ffffc90000197df8 EFLAGS: 000002c2
> RAX: 000000000015fae9 RBX: 0000000000000001 RCX: ffffffff8b93fc29
> RDX: 0000000000000000 RSI: ffffffff8de50a38 RDI: ffffffff8c162980
> RBP: ffffed1003c5d488 R08: 0000000000000001 R09: ffffed10170a6655
> R10: ffff8880b85332ab R11: 0000000000000000 R12: 0000000000000001
> R13: ffff88801e2ea440 R14: ffffffff90ab5290 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff8881247b8000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000555d26767660 CR3: 000000000e380000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
>  default_idle+0x13/0x20 arch/x86/kernel/process.c:757
>  default_idle_call+0x6d/0xb0 kernel/sched/idle.c:122
>  cpuidle_idle_call kernel/sched/idle.c:190 [inline]
>  do_idle+0x391/0x510 kernel/sched/idle.c:330
>  cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:428
>  start_secondary+0x21d/0x2b0 arch/x86/kernel/smpboot.c:315
>  common_startup_64+0x13e/0x148
>  </TASK>
> 
> 
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.


#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 34cf9ba5f00a222dddd9fc71de7c68fdaac7fb97