3.16.80-rc1 review patch. If anyone has any objections, please let me know.
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From: Takashi Iwai tiwai@suse.de
commit a39331867335d4a94b6165e306265c9e24aca073 upstream.
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 Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Ben Hutchings ben@decadent.org.uk --- sound/core/timer.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-)
--- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -241,7 +241,8 @@ static int snd_timer_check_master(struct 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 @@ -253,6 +254,7 @@ int snd_timer_open(struct snd_timer_inst { struct snd_timer *timer; struct snd_timer_instance *timeri = NULL; + struct device *card_dev_to_put = NULL; int err;
mutex_lock(®ister_mutex); @@ -276,7 +278,7 @@ int snd_timer_open(struct snd_timer_inst 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; @@ -328,7 +330,7 @@ int snd_timer_open(struct snd_timer_inst 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; } @@ -338,12 +340,15 @@ int snd_timer_open(struct snd_timer_inst 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; } @@ -352,7 +357,8 @@ int snd_timer_open(struct snd_timer_inst * 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 = NULL; struct snd_timer_instance *slave, *tmp; @@ -404,7 +410,7 @@ static int snd_timer_close_locked(struct 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); }
@@ -416,14 +422,18 @@ static int snd_timer_close_locked(struct */ 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; }