The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From a39331867335d4a94b6165e306265c9e24aca073 Mon Sep 17 00:00:00 2001
From: Takashi Iwai tiwai@suse.de Date: Wed, 30 Oct 2019 22:42:57 +0100 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
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(®ister_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(®ister_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(®ister_mutex); - err = snd_timer_close_locked(timeri); + err = snd_timer_close_locked(timeri, &card_dev_to_put); mutex_unlock(®ister_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);