On Wed, 30 Oct 2019 16:28:23 +0100, Kirill A. Shutemov wrote:

On Wed, Oct 30, 2019 at 06:11:37PM +0300, Kirill A. Shutemov wrote:

...

On Wed, Oct 30, 2019 at 04:04:01PM +0100, Takashi Iwai wrote:

...

On Wed, 30 Oct 2019 15:10:29 +0100, Kirill A. Shutemov wrote:

...

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)

OK, this looks like a deadlock that is via put_device() called at closing the timer device that is the last open instance while freeing the card.

Could you try the patch below?

I can, but I'm not sure if I can trigger the issue for the second time.

Yeah, I was able to reproduce it without the patch and cannot with.

Reported-and-tested-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com

Great, thanks for quick testing!

FWIW, below is the proper patch with the description I'm going to queue.

Takashi

-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: timer: Fix mutex deadlock at releasing card

When a card is disconnected while in use, the system waits until all opened files are closed then releases the card. This is done via put_device() of the card device in each device release code.

The recently reported mutex deadlock bug happens in this code path; snd_timer_close() for the timer device deals with the global register_mutex and it calls put_device() there. When this timer device is the last one, the card gets freed and it eventually calls snd_timer_free(), which has again the protection with the global register_mutex -- boom.

Basically put_device() call itself is race-free, so a relative simple workaround is to move this put_device() call out of the mutex. For achieving that, in this patch, snd_timer_close_locked() got a new argument to store the card device pointer in return, and each caller invokes put_device() with the returned object after the mutex unlock.

Reported-and-tested-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/core/timer.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/sound/core/timer.c b/sound/core/timer.c index 5c9fbf3f4340..6b724d2ee2de 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -226,7 +226,8 @@ static int snd_timer_check_master(struct snd_timer_instance *master) return 0; }

-static int snd_timer_close_locked(struct snd_timer_instance *timeri); +static int snd_timer_close_locked(struct snd_timer_instance *timeri, + struct device **card_devp_to_put);

/* * open a timer instance @@ -238,6 +239,7 @@ int snd_timer_open(struct snd_timer_instance **ti, { struct snd_timer *timer; struct snd_timer_instance *timeri = NULL; + struct device *card_dev_to_put = NULL; int err;

mutex_lock(&register_mutex); @@ -261,7 +263,7 @@ int snd_timer_open(struct snd_timer_instance **ti, list_add_tail(&timeri->open_list, &snd_timer_slave_list); err = snd_timer_check_slave(timeri); if (err < 0) { - snd_timer_close_locked(timeri); + snd_timer_close_locked(timeri, &card_dev_to_put); timeri = NULL; } goto unlock; @@ -313,7 +315,7 @@ int snd_timer_open(struct snd_timer_instance **ti, timeri = NULL;

if (timer->card) - put_device(&timer->card->card_dev); + card_dev_to_put = &timer->card->card_dev; module_put(timer->module); goto unlock; } @@ -323,12 +325,15 @@ int snd_timer_open(struct snd_timer_instance **ti, timer->num_instances++; err = snd_timer_check_master(timeri); if (err < 0) { - snd_timer_close_locked(timeri); + snd_timer_close_locked(timeri, &card_dev_to_put); timeri = NULL; }

unlock: mutex_unlock(&register_mutex); + /* put_device() is called after unlock for avoiding deadlock */ + if (card_dev_to_put) + put_device(card_dev_to_put); *ti = timeri; return err; } @@ -338,7 +343,8 @@ EXPORT_SYMBOL(snd_timer_open); * close a timer instance * call this with register_mutex down. */ -static int snd_timer_close_locked(struct snd_timer_instance *timeri) +static int snd_timer_close_locked(struct snd_timer_instance *timeri, + struct device **card_devp_to_put) { struct snd_timer *timer = timeri->timer; struct snd_timer_instance *slave, *tmp; @@ -395,7 +401,7 @@ static int snd_timer_close_locked(struct snd_timer_instance *timeri) timer->hw.close(timer); /* release a card refcount for safe disconnection */ if (timer->card) - put_device(&timer->card->card_dev); + *card_devp_to_put = &timer->card->card_dev; module_put(timer->module); }

@@ -407,14 +413,18 @@ static int snd_timer_close_locked(struct snd_timer_instance *timeri) */ int snd_timer_close(struct snd_timer_instance *timeri) { + struct device *card_dev_to_put = NULL; int err;

if (snd_BUG_ON(!timeri)) return -ENXIO;

mutex_lock(&register_mutex); - err = snd_timer_close_locked(timeri); + err = snd_timer_close_locked(timeri, &card_dev_to_put); mutex_unlock(&register_mutex); + /* put_device() is called after unlock for avoiding deadlock */ + if (card_dev_to_put) + put_device(card_dev_to_put); return err; } EXPORT_SYMBOL(snd_timer_close);