[alsa-devel] [PATCH 1/2] ALSA: timer: Protect the whole snd_timer_close() with open race
In order to make the open/close more robust, widen the register_mutex protection over the whole snd_timer_close() function. Also, the close procedure is slightly shuffled to be in the safer order, as well as a few code refactoring. Signed-off-by: Takashi Iwai <tiwai@suse.de> --- This is no urgent fix, so queued for 4.6. sound/core/timer.c | 48 +++++++++++++++++++++--------------------------- 1 file changed, 21 insertions(+), 27 deletions(-) diff --git a/sound/core/timer.c b/sound/core/timer.c index dca817fc7894..b572a9bc31ad 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -318,25 +318,14 @@ int snd_timer_close(struct snd_timer_instance *timeri) if (snd_BUG_ON(!timeri)) return -ENXIO; + mutex_lock(®ister_mutex); + list_del(&timeri->open_list); + /* force to stop the timer */ snd_timer_stop(timeri); - if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) { - /* wait, until the active callback is finished */ - spin_lock_irq(&slave_active_lock); - while (timeri->flags & SNDRV_TIMER_IFLG_CALLBACK) { - spin_unlock_irq(&slave_active_lock); - udelay(10); - spin_lock_irq(&slave_active_lock); - } - spin_unlock_irq(&slave_active_lock); - mutex_lock(®ister_mutex); - list_del(&timeri->open_list); - mutex_unlock(®ister_mutex); - } else { - timer = timeri->timer; - if (snd_BUG_ON(!timer)) - goto out; + timer = timeri->timer; + if (timer) { /* wait, until the active callback is finished */ spin_lock_irq(&timer->lock); while (timeri->flags & SNDRV_TIMER_IFLG_CALLBACK) { @@ -345,11 +334,7 @@ int snd_timer_close(struct snd_timer_instance *timeri) spin_lock_irq(&timer->lock); } spin_unlock_irq(&timer->lock); - mutex_lock(®ister_mutex); - list_del(&timeri->open_list); - if (list_empty(&timer->open_list_head) && - timer->hw.close) - timer->hw.close(timer); + /* remove slave links */ spin_lock_irq(&slave_active_lock); spin_lock(&timer->lock); @@ -363,18 +348,27 @@ int snd_timer_close(struct snd_timer_instance *timeri) } spin_unlock(&timer->lock); spin_unlock_irq(&slave_active_lock); - /* release a card refcount for safe disconnection */ - if (timer->card) - put_device(&timer->card->card_dev); - mutex_unlock(®ister_mutex); + + /* slave doesn't need to release timer resources below */ + if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) + timer = NULL; } - out: + if (timeri->private_free) timeri->private_free(timeri); kfree(timeri->owner); kfree(timeri); - if (timer) + + if (timer) { + if (list_empty(&timer->open_list_head) && timer->hw.close) + timer->hw.close(timer); + /* release a card refcount for safe disconnection */ + if (timer->card) + put_device(&timer->card->card_dev); module_put(timer->module); + } + + mutex_unlock(®ister_mutex); return 0; } -- 2.7.1
snd_timer_notify1() is called outside the spinlock and it retakes the lock after the unlock. This is rather racy, and it's safer to move snd_timer_notify() call inside the main spinlock. The patch also contains a slight refactoring / cleanup of the code. Not all start/stop/continue/pause look more symmetric and a bit better readable. Signed-off-by: Takashi Iwai <tiwai@suse.de> --- sound/core/timer.c | 220 +++++++++++++++++++++++++---------------------------- 1 file changed, 102 insertions(+), 118 deletions(-) diff --git a/sound/core/timer.c b/sound/core/timer.c index b572a9bc31ad..aa1b15c155d1 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -305,8 +305,6 @@ int snd_timer_open(struct snd_timer_instance **ti, return 0; } -static int _snd_timer_stop(struct snd_timer_instance *timeri, int event); - /* * close a timer instance */ @@ -389,7 +387,6 @@ unsigned long snd_timer_resolution(struct snd_timer_instance *timeri) static void snd_timer_notify1(struct snd_timer_instance *ti, int event) { struct snd_timer *timer; - unsigned long flags; unsigned long resolution = 0; struct snd_timer_instance *ts; struct timespec tstamp; @@ -413,34 +410,66 @@ static void snd_timer_notify1(struct snd_timer_instance *ti, int event) return; if (timer->hw.flags & SNDRV_TIMER_HW_SLAVE) return; - spin_lock_irqsave(&timer->lock, flags); list_for_each_entry(ts, &ti->slave_active_head, active_list) if (ts->ccallback) ts->ccallback(ts, event + 100, &tstamp, resolution); - spin_unlock_irqrestore(&timer->lock, flags); } -static int snd_timer_start1(struct snd_timer *timer, struct snd_timer_instance *timeri, - unsigned long sticks) +/* start/continue a master timer */ +static int snd_timer_start1(struct snd_timer_instance *timeri, + bool start, unsigned long ticks) { + struct snd_timer *timer; + int result; + unsigned long flags; + + timer = timeri->timer; + if (!timer) + return -EINVAL; + + spin_lock_irqsave(&timer->lock, flags); + if (timer->card && timer->card->shutdown) { + result = -ENODEV; + goto unlock; + } + if (timeri->flags & (SNDRV_TIMER_IFLG_RUNNING | + SNDRV_TIMER_IFLG_START)) { + result = -EBUSY; + goto unlock; + } + + if (start) + timeri->ticks = timeri->cticks = ticks; + else if (!timeri->cticks) + timeri->cticks = 1; + timeri->pticks = 0; + list_move_tail(&timeri->active_list, &timer->active_list_head); if (timer->running) { if (timer->hw.flags & SNDRV_TIMER_HW_SLAVE) goto __start_now; timer->flags |= SNDRV_TIMER_FLG_RESCHED; timeri->flags |= SNDRV_TIMER_IFLG_START; - return 1; /* delayed start */ + result = 1; /* delayed start */ } else { - timer->sticks = sticks; + if (start) + timer->sticks = ticks; timer->hw.start(timer); __start_now: timer->running++; timeri->flags |= SNDRV_TIMER_IFLG_RUNNING; - return 0; + result = 0; } + snd_timer_notify1(timeri, start ? SNDRV_TIMER_EVENT_START : + SNDRV_TIMER_EVENT_CONTINUE); + unlock: + spin_unlock_irqrestore(&timer->lock, flags); + return result; } -static int snd_timer_start_slave(struct snd_timer_instance *timeri) +/* start/continue a slave timer */ +static int snd_timer_start_slave(struct snd_timer_instance *timeri, + bool start) { unsigned long flags; @@ -454,88 +483,37 @@ static int snd_timer_start_slave(struct snd_timer_instance *timeri) spin_lock(&timeri->timer->lock); list_add_tail(&timeri->active_list, &timeri->master->slave_active_head); + snd_timer_notify1(timeri, start ? SNDRV_TIMER_EVENT_START : + SNDRV_TIMER_EVENT_CONTINUE); spin_unlock(&timeri->timer->lock); } spin_unlock_irqrestore(&slave_active_lock, flags); return 1; /* delayed start */ } -/* - * start the timer instance - */ -int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks) -{ - struct snd_timer *timer; - int result = -EINVAL; - unsigned long flags; - - if (timeri == NULL || ticks < 1) - return -EINVAL; - if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) { - result = snd_timer_start_slave(timeri); - if (result >= 0) - snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); - return result; - } - timer = timeri->timer; - if (timer == NULL) - return -EINVAL; - if (timer->card && timer->card->shutdown) - return -ENODEV; - spin_lock_irqsave(&timer->lock, flags); - if (timeri->flags & (SNDRV_TIMER_IFLG_RUNNING | - SNDRV_TIMER_IFLG_START)) { - result = -EBUSY; - goto unlock; - } - timeri->ticks = timeri->cticks = ticks; - timeri->pticks = 0; - result = snd_timer_start1(timer, timeri, ticks); - unlock: - spin_unlock_irqrestore(&timer->lock, flags); - if (result >= 0) - snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); - return result; -} - -static int _snd_timer_stop(struct snd_timer_instance *timeri, int event) +/* stop/pause a master timer */ +static int snd_timer_stop1(struct snd_timer_instance *timeri, bool stop) { struct snd_timer *timer; + int result = 0; unsigned long flags; - if (snd_BUG_ON(!timeri)) - return -ENXIO; - - if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) { - spin_lock_irqsave(&slave_active_lock, flags); - if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) { - spin_unlock_irqrestore(&slave_active_lock, flags); - return -EBUSY; - } - if (timeri->timer) - spin_lock(&timeri->timer->lock); - timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING; - list_del_init(&timeri->ack_list); - list_del_init(&timeri->active_list); - if (timeri->timer) - spin_unlock(&timeri->timer->lock); - spin_unlock_irqrestore(&slave_active_lock, flags); - goto __end; - } timer = timeri->timer; if (!timer) return -EINVAL; spin_lock_irqsave(&timer->lock, flags); if (!(timeri->flags & (SNDRV_TIMER_IFLG_RUNNING | SNDRV_TIMER_IFLG_START))) { - spin_unlock_irqrestore(&timer->lock, flags); - return -EBUSY; + result = -EBUSY; + goto unlock; } list_del_init(&timeri->ack_list); list_del_init(&timeri->active_list); - if (timer->card && timer->card->shutdown) { - spin_unlock_irqrestore(&timer->lock, flags); - return 0; + if (timer->card && timer->card->shutdown) + goto unlock; + if (stop) { + timeri->cticks = timeri->ticks; + timeri->pticks = 0; } if ((timeri->flags & SNDRV_TIMER_IFLG_RUNNING) && !(--timer->running)) { @@ -550,35 +528,60 @@ static int _snd_timer_stop(struct snd_timer_instance *timeri, int event) } } timeri->flags &= ~(SNDRV_TIMER_IFLG_RUNNING | SNDRV_TIMER_IFLG_START); + snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP : + SNDRV_TIMER_EVENT_CONTINUE); + unlock: spin_unlock_irqrestore(&timer->lock, flags); - __end: - if (event != SNDRV_TIMER_EVENT_RESOLUTION) - snd_timer_notify1(timeri, event); + return result; +} + +/* stop/pause a slave timer */ +static int snd_timer_stop_slave(struct snd_timer_instance *timeri, bool stop) +{ + unsigned long flags; + + spin_lock_irqsave(&slave_active_lock, flags); + if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) { + spin_unlock_irqrestore(&slave_active_lock, flags); + return -EBUSY; + } + timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING; + if (timeri->timer) { + spin_lock(&timeri->timer->lock); + list_del_init(&timeri->ack_list); + list_del_init(&timeri->active_list); + snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP : + SNDRV_TIMER_EVENT_CONTINUE); + spin_unlock(&timeri->timer->lock); + } + spin_unlock_irqrestore(&slave_active_lock, flags); return 0; } /* + * start the timer instance + */ +int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks) +{ + if (timeri == NULL || ticks < 1) + return -EINVAL; + if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) + return snd_timer_start_slave(timeri, true); + else + return snd_timer_start1(timeri, true, ticks); +} + +/* * stop the timer instance. * * do not call this from the timer callback! */ int snd_timer_stop(struct snd_timer_instance *timeri) { - struct snd_timer *timer; - unsigned long flags; - int err; - - err = _snd_timer_stop(timeri, SNDRV_TIMER_EVENT_STOP); - if (err < 0) - return err; - timer = timeri->timer; - if (!timer) - return -EINVAL; - spin_lock_irqsave(&timer->lock, flags); - timeri->cticks = timeri->ticks; - timeri->pticks = 0; - spin_unlock_irqrestore(&timer->lock, flags); - return 0; + if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) + return snd_timer_stop_slave(timeri, true); + else + return snd_timer_stop1(timeri, true); } /* @@ -586,32 +589,10 @@ int snd_timer_stop(struct snd_timer_instance *timeri) */ int snd_timer_continue(struct snd_timer_instance *timeri) { - struct snd_timer *timer; - int result = -EINVAL; - unsigned long flags; - - if (timeri == NULL) - return result; if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) - return snd_timer_start_slave(timeri); - timer = timeri->timer; - if (! timer) - return -EINVAL; - if (timer->card && timer->card->shutdown) - return -ENODEV; - spin_lock_irqsave(&timer->lock, flags); - if (timeri->flags & SNDRV_TIMER_IFLG_RUNNING) { - result = -EBUSY; - goto unlock; - } - if (!timeri->cticks) - timeri->cticks = 1; - timeri->pticks = 0; - result = snd_timer_start1(timer, timeri, timer->sticks); - unlock: - spin_unlock_irqrestore(&timer->lock, flags); - snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_CONTINUE); - return result; + return snd_timer_start_slave(timeri, false); + else + return snd_timer_start1(timeri, false, 0); } /* @@ -619,7 +600,10 @@ int snd_timer_continue(struct snd_timer_instance *timeri) */ int snd_timer_pause(struct snd_timer_instance * timeri) { - return _snd_timer_stop(timeri, SNDRV_TIMER_EVENT_PAUSE); + if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) + return snd_timer_stop_slave(timeri, false); + else + return snd_timer_stop1(timeri, false); } /* -- 2.7.1
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Takashi Iwai