Hi,
I've stepped on this after pulling USB sound card:
============================================ WARNING: possible recursive locking detected 5.4.0-rc4-00090-g95b5dc072cc3-dirty #48 Not tainted -------------------------------------------- xdg-screensaver/1321 is trying to acquire lock: ffffffffbaf6b3a0 (register_mutex){+.+.}, at: snd_timer_free.part.0 (/include/linux/compiler.h:199 /include/linux/list.h:268 /sound/core/timer.c:944)
but task is already holding lock: ffffffffbaf6b3a0 (register_mutex){+.+.}, at: snd_timer_close (/sound/core/timer.c:416)
other info that might help us debug this: Possible unsafe locking scenario:
CPU0 ---- lock(register_mutex); lock(register_mutex);
*** DEADLOCK ***
May be due to missing lock nesting notation
2 locks held by xdg-screensaver/1321: #0: ffff9f74bbf5ef50 (&tu->ioctl_lock){+.+.}, at: snd_timer_user_release (/sound/core/timer.c:1467) #1: ffffffffbaf6b3a0 (register_mutex){+.+.}, at: snd_timer_close (/sound/core/timer.c:416)
stack backtrace: CPU: 27 PID: 1321 Comm: xdg-screensaver Not tainted 5.4.0-rc4-00090-g95b5dc072cc3-dirty #48 Hardware name: Gigabyte Technology Co., Ltd. X299 AORUS Gaming 3 Pro/X299 AORUS Gaming 3 Pro-CF, BIOS F3 12/28/2017 Call Trace: dump_stack (/lib/dump_stack.c:115) __lock_acquire.cold (/kernel/locking/lockdep.c:2371 /kernel/locking/lockdep.c:2412 /kernel/locking/lockdep.c:2955 /kernel/locking/lockdep.c:3955) ? __lock_acquire (/kernel/locking/lockdep.c:3962) lock_acquire (/arch/x86/include/asm/current.h:15 /kernel/locking/lockdep.c:4489) ? snd_timer_free.part.0 (/include/linux/compiler.h:199 /include/linux/list.h:268 /sound/core/timer.c:944) __mutex_lock (/include/linux/compiler.h:199 /arch/x86/include/asm/atomic64_64.h:22 /include/asm-generic/atomic-instrumented.h:837 /include/asm-generic/atomic-long.h:28 /kernel/locking/mutex.c:111 /kernel/locking/mutex.c:152 /kernel/locking/mutex.c:958 /kernel/locking/mutex.c:1103) ? snd_timer_free.part.0 (/include/linux/compiler.h:199 /include/linux/list.h:268 /sound/core/timer.c:944) ? __mutex_lock (/include/linux/compiler.h:199 /arch/x86/include/asm/atomic64_64.h:22 /include/asm-generic/atomic-instrumented.h:837 /include/asm-generic/atomic-long.h:28 /kernel/locking/mutex.c:111 /kernel/locking/mutex.c:152 /kernel/locking/mutex.c:958 /kernel/locking/mutex.c:1103) ? __mutex_lock (/arch/x86/include/asm/preempt.h:102 /kernel/locking/mutex.c:964 /kernel/locking/mutex.c:1103) ? snd_timer_free.part.0 (/include/linux/compiler.h:199 /include/linux/list.h:268 /sound/core/timer.c:944) ? snd_timer_free.part.0 (/include/linux/compiler.h:199 /include/linux/list.h:268 /sound/core/timer.c:944) ? lockdep_hardirqs_on (/kernel/locking/lockdep.c:3394 /kernel/locking/lockdep.c:3434) snd_timer_free.part.0 (/include/linux/compiler.h:199 /include/linux/list.h:268 /sound/core/timer.c:944) snd_timer_dev_free (/sound/core/timer.c:967) __snd_device_free (/sound/core/device.c:76) snd_device_free_all (/sound/core/device.c:228) release_card_device (/sound/core/init.c:471 /sound/core/init.c:140) device_release (/drivers/base/core.c:1105) kobject_put (/lib/kobject.c:697 /lib/kobject.c:722 /include/linux/kref.h:65 /lib/kobject.c:739) snd_timer_close_locked (/sound/core/timer.c:398) snd_timer_close (/sound/core/timer.c:417) snd_timer_user_release (/sound/core/timer.c:1469) __fput (/fs/file_table.c:281) task_work_run (/kernel/task_work.c:115 (discriminator 1)) exit_to_usermode_loop (/include/linux/tracehook.h:188 /arch/x86/entry/common.c:163) do_syscall_64 (/arch/x86/entry/common.c:194 /arch/x86/entry/common.c:274 /arch/x86/entry/common.c:300) entry_SYSCALL_64_after_hwframe (/arch/x86/entry/entry_64.S:177)
-- Kirill A. Shutemov