usb 1-1: USB disconnect, device number 2
======================================================
WARNING: possible circular locking dependency detected
5.3.0+ #0 Not tainted
------------------------------------------------------
kworker/0:1/12 is trying to acquire lock:
ffffffff874267c8 (minor_rwsem){++++}, at: usb_deregister_dev+0x95/0x230 drivers/usb/core/file.c:239

but task is already holding lock:
ffffffff874c5620 (open_disc_mutex){+.+.}, at: tower_disconnect+0x45/0x300 drivers/usb/misc/legousbtower.c:945

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (open_disc_mutex){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:956 [inline]
       __mutex_lock+0x158/0x1360 kernel/locking/mutex.c:1103
       tower_open+0xce/0x9b0 drivers/usb/misc/legousbtower.c:335
       usb_open+0x1df/0x270 drivers/usb/core/file.c:48
       chrdev_open+0x219/0x5c0 fs/char_dev.c:414
       do_dentry_open+0x494/0x1120 fs/open.c:797
       do_last fs/namei.c:3408 [inline]
       path_openat+0x1430/0x3f50 fs/namei.c:3525
       do_filp_open+0x1a1/0x280 fs/namei.c:3555
       do_sys_open+0x3c0/0x580 fs/open.c:1097
       do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (minor_rwsem){++++}:
       check_prev_add kernel/locking/lockdep.c:2476 [inline]
       check_prevs_add kernel/locking/lockdep.c:2581 [inline]
       validate_chain kernel/locking/lockdep.c:2971 [inline]
       __lock_acquire+0x1f74/0x3eb0 kernel/locking/lockdep.c:3955
       lock_acquire+0x127/0x320 kernel/locking/lockdep.c:4487
       down_write+0x92/0x150 kernel/locking/rwsem.c:1534
       usb_deregister_dev+0x95/0x230 drivers/usb/core/file.c:239
       tower_disconnect+0xa8/0x300 drivers/usb/misc/legousbtower.c:951
       usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:423
       __device_release_driver drivers/base/dd.c:1134 [inline]
       device_release_driver_internal+0x42f/0x500 drivers/base/dd.c:1165
       bus_remove_device+0x2dc/0x4a0 drivers/base/bus.c:532
       device_del+0x420/0xb10 drivers/base/core.c:2375
       usb_disable_device+0x211/0x690 drivers/usb/core/message.c:1237
       usb_disconnect+0x284/0x8d0 drivers/usb/core/hub.c:2199
       hub_port_connect drivers/usb/core/hub.c:4949 [inline]
       hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
       port_event drivers/usb/core/hub.c:5359 [inline]
       hub_event+0x1454/0x3640 drivers/usb/core/hub.c:5441
       process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
       worker_thread+0x96/0xe20 kernel/workqueue.c:2415
       kthread+0x318/0x420 kernel/kthread.c:255
       ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(open_disc_mutex);
                               lock(minor_rwsem);
                               lock(open_disc_mutex);
  lock(minor_rwsem);

 *** DEADLOCK ***

6 locks held by kworker/0:1/12:
 #0: ffff8881d9799ca8 ((wq_completion)usb_hub_wq){+.+.}, at: __write_once_size include/linux/compiler.h:226 [inline]
 #0: ffff8881d9799ca8 ((wq_completion)usb_hub_wq){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff8881d9799ca8 ((wq_completion)usb_hub_wq){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:855 [inline]
 #0: ffff8881d9799ca8 ((wq_completion)usb_hub_wq){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:40 [inline]
 #0: ffff8881d9799ca8 ((wq_completion)usb_hub_wq){+.+.}, at: set_work_data kernel/workqueue.c:620 [inline]
 #0: ffff8881d9799ca8 ((wq_completion)usb_hub_wq){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:647 [inline]
 #0: ffff8881d9799ca8 ((wq_completion)usb_hub_wq){+.+.}, at: process_one_work+0x827/0x1530 kernel/workqueue.c:2240
 #1: ffff8881da20fdd0 ((work_completion)(&hub->events)){+.+.}, at: process_one_work+0x85b/0x1530 kernel/workqueue.c:2244
 #2: ffff8881d5ca7080 (&dev->mutex){....}, at: device_lock include/linux/device.h:1462 [inline]
 #2: ffff8881d5ca7080 (&dev->mutex){....}, at: hub_event+0x17c/0x3640 drivers/usb/core/hub.c:5387
 #3: ffff8881d30e6800 (&dev->mutex){....}, at: device_lock include/linux/device.h:1462 [inline]
 #3: ffff8881d30e6800 (&dev->mutex){....}, at: usb_disconnect+0x91/0x8d0 drivers/usb/core/hub.c:2190
 #4: ffff8881d30e7010 (&dev->mutex){....}, at: device_release_driver_internal+0x23/0x500 drivers/base/dd.c:1162
 #5: ffffffff874c5620 (open_disc_mutex){+.+.}, at: tower_disconnect+0x45/0x300 drivers/usb/misc/legousbtower.c:945

stack backtrace:
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.3.0+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: usb_hub_wq hub_event
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xca/0x13e lib/dump_stack.c:113
 check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1809
 check_prev_add kernel/locking/lockdep.c:2476 [inline]
 check_prevs_add kernel/locking/lockdep.c:2581 [inline]
 validate_chain kernel/locking/lockdep.c:2971 [inline]
 __lock_acquire+0x1f74/0x3eb0 kernel/locking/lockdep.c:3955
 lock_acquire+0x127/0x320 kernel/locking/lockdep.c:4487
 down_write+0x92/0x150 kernel/locking/rwsem.c:1534
 usb_deregister_dev+0x95/0x230 drivers/usb/core/file.c:239
 tower_disconnect+0xa8/0x300 drivers/usb/misc/legousbtower.c:951
 usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:423
 __device_release_driver drivers/base/dd.c:1134 [inline]
 device_release_driver_internal+0x42f/0x500 drivers/base/dd.c:1165
 bus_remove_device+0x2dc/0x4a0 drivers/base/bus.c:532
 device_del+0x420/0xb10 drivers/base/core.c:2375
 usb_disable_device+0x211/0x690 drivers/usb/core/message.c:1237
 usb_disconnect+0x284/0x8d0 drivers/usb/core/hub.c:2199
 hub_port_connect drivers/usb/core/hub.c:4949 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
 port_event drivers/usb/core/hub.c:5359 [inline]
 hub_event+0x1454/0x3640 drivers/usb/core/hub.c:5441
 process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
 ? pwq_de