INFO: task hung in __do_sys_reboot

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    768a0741 usb: dwc2: gadget: Remove assigned but never used..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
console output: https://syzkaller.appspot.com/x/log.txt?x=14ec52b7100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=999be4eb2478ffa5
dashboard link: https://syzkaller.appspot.com/bug?extid=805f5f6ae37411f15b64
compiler:       gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+805f5f6ae37411f15b64@xxxxxxxxxxxxxxxxxxxxxxxxx

INFO: task systemd-shutdow:1 blocked for more than 143 seconds.
      Not tainted 5.8.0-rc3-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
systemd-shutdow D24504     1      0 0x00004000
Call Trace:
 context_switch kernel/sched/core.c:3453 [inline]
 __schedule+0x88a/0x1cb0 kernel/sched/core.c:4178
 schedule+0xcd/0x2b0 kernel/sched/core.c:4253
 wait_for_device_probe+0x1be/0x220 drivers/base/dd.c:665
 device_shutdown+0x18/0x5b5 drivers/base/core.c:3748
 kernel_restart_prepare kernel/reboot.c:76 [inline]
 kernel_restart kernel/reboot.c:246 [inline]
 __do_sys_reboot.cold+0x5d/0x9d kernel/reboot.c:347
 do_syscall_64+0x50/0x90 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fc0c04788c6
Code: Bad RIP value.
RSP: 002b:00007fff74038008 EFLAGS: 00000202 ORIG_RAX: 00000000000000a9
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc0c04788c6
RDX: 0000000001234567 RSI: 0000000028121969 RDI: fffffffffee1dead
RBP: 00007fff74038098 R08: 0000000000000028 R09: 0000000000000005
R10: 0000000000000002 R11: 0000000000000202 R12: 0000000000000000
R13: 0000000000000000 R14: 000055b9797c9150 R15: 00007fff74038388

Showing all locks held in the system:
1 lock held by systemd-shutdow/1:
 #0: ffffffff872e8f68 (system_transition_mutex){+.+.}-{3:3}, at: __do_sys_reboot+0x1a4/0x3e0 kernel/reboot.c:344
1 lock held by khungtaskd/23:
 #0: ffffffff873124a0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x264 kernel/locking/lockdep.c:5779
5 locks held by kworker/1:2/67:
 #0: ffff8881d880ed38 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff8881d880ed38 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
 #0: ffff8881d880ed38 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
 #0: ffff8881d880ed38 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
 #0: ffff8881d880ed38 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0: ffff8881d880ed38 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_one_work+0x82b/0x15f0 kernel/workqueue.c:2240
 #1: ffff8881d583fda8 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_one_work+0x85f/0x15f0 kernel/workqueue.c:2244
 #2: ffff8881d450a218 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:768 [inline]
 #2: ffff8881d450a218 (&dev->mutex){....}-{3:3}, at: hub_event+0x1c5/0x4390 drivers/usb/core/hub.c:5522
 #3: ffff8881d23a4218 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:768 [inline]
 #3: ffff8881d23a4218 (&dev->mutex){....}-{3:3}, at: __device_attach+0x7a/0x430 drivers/base/dd.c:850
 #4: ffff8881ab7591a8 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:768 [inline]
 #4: ffff8881ab7591a8 (&dev->mutex){....}-{3:3}, at: __device_attach+0x7a/0x430 drivers/base/dd.c:850

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 23 Comm: khungtaskd Not tainted 5.8.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xf6/0x16e lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x74/0xb6 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1da/0x1f4 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:209 [inline]
 watchdog+0xd6a/0xfd0 kernel/hung_task.c:295
 kthread+0x392/0x470 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
NMI backtrace for cpu 1 skipped: idling at acpi_safe_halt+0x72/0x90 drivers/acpi/processor_idle.c:111


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