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authorTakashi Iwai <tiwai@suse.de>2016-04-24 22:52:18 +0200
committerTakashi Iwai <tiwai@suse.de>2016-04-26 09:34:40 +0200
commitd2c5cf88d5282de258f4eb6ab40040b80a075cd8 (patch)
treef21c1cf7e4da494db9a36c3dab1c65aed1c4e9fb /sound/core
parent8d84c1973b69621bcb89d5d8a69699e8347a3d90 (diff)
downloadlinux-d2c5cf88d5282de258f4eb6ab40040b80a075cd8.tar.bz2
ALSA: hrtimer: Handle start/stop more properly
This patch tries to address the still remaining issues in ALSA hrtimer driver: - Spurious use-after-free was detected in hrtimer callback - Incorrect rescheduling due to delayed start - WARN_ON() is triggered in hrtimer_forward() invoked in hrtimer callback The first issue happens only when the new timer is scheduled even while hrtimer is being closed. It's related with the second and third items; since ALSA timer core invokes hw.start callback during hrtimer interrupt, this may result in the explicit call of hrtimer_start(). Also, the similar problem is seen for the stop; ALSA timer core invokes hw.stop callback even in the hrtimer handler, too. Since we must not call the synced hrtimer_cancel() in such a context, it's just a hrtimer_try_to_cancel() call that doesn't properly work. Another culprit of the second and third items is the call of hrtimer_forward_now() before snd_timer_interrupt(). The timer->stick value may change during snd_timer_interrupt() call, but this possibility is ignored completely. For covering these subtle and messy issues, the following changes have been done in this patch: - A new flag, in_callback, is introduced in the private data to indicate that the hrtimer handler is being processed. - Both start and stop callbacks skip when called from (during) in_callback flag. - The hrtimer handler returns properly HRTIMER_RESTART and NORESTART depending on the running state now. - The hrtimer handler reprograms the expiry properly after snd_timer_interrupt() call, instead of before. - The close callback clears running flag and sets in_callback flag to block any further start/stop calls. Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/core')
-rw-r--r--sound/core/hrtimer.c56
1 files changed, 39 insertions, 17 deletions
diff --git a/sound/core/hrtimer.c b/sound/core/hrtimer.c
index 656d9a9032dc..e2f27022b363 100644
--- a/sound/core/hrtimer.c
+++ b/sound/core/hrtimer.c
@@ -38,37 +38,53 @@ static unsigned int resolution;
struct snd_hrtimer {
struct snd_timer *timer;
struct hrtimer hrt;
- atomic_t running;
+ bool in_callback;
};
static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
{
struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
struct snd_timer *t = stime->timer;
- unsigned long oruns;
-
- if (!atomic_read(&stime->running))
- return HRTIMER_NORESTART;
-
- oruns = hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
- snd_timer_interrupt(stime->timer, t->sticks * oruns);
+ ktime_t delta;
+ unsigned long ticks;
+ enum hrtimer_restart ret = HRTIMER_NORESTART;
+
+ spin_lock(&t->lock);
+ if (!t->running)
+ goto out; /* fast path */
+ stime->in_callback = true;
+ ticks = t->sticks;
+ spin_unlock(&t->lock);
+
+ /* calculate the drift */
+ delta = ktime_sub(hrt->base->get_time(), hrtimer_get_expires(hrt));
+ if (delta.tv64 > 0)
+ ticks += ktime_divns(delta, ticks * resolution);
+
+ snd_timer_interrupt(stime->timer, ticks);
+
+ spin_lock(&t->lock);
+ if (t->running) {
+ hrtimer_add_expires_ns(hrt, t->sticks * resolution);
+ ret = HRTIMER_RESTART;
+ }
- if (!atomic_read(&stime->running))
- return HRTIMER_NORESTART;
- return HRTIMER_RESTART;
+ stime->in_callback = false;
+ out:
+ spin_unlock(&t->lock);
+ return ret;
}
static int snd_hrtimer_open(struct snd_timer *t)
{
struct snd_hrtimer *stime;
- stime = kmalloc(sizeof(*stime), GFP_KERNEL);
+ stime = kzalloc(sizeof(*stime), GFP_KERNEL);
if (!stime)
return -ENOMEM;
hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
stime->timer = t;
stime->hrt.function = snd_hrtimer_callback;
- atomic_set(&stime->running, 0);
t->private_data = stime;
return 0;
}
@@ -78,6 +94,11 @@ static int snd_hrtimer_close(struct snd_timer *t)
struct snd_hrtimer *stime = t->private_data;
if (stime) {
+ spin_lock_irq(&t->lock);
+ t->running = 0; /* just to be sure */
+ stime->in_callback = 1; /* skip start/stop */
+ spin_unlock_irq(&t->lock);
+
hrtimer_cancel(&stime->hrt);
kfree(stime);
t->private_data = NULL;
@@ -89,18 +110,19 @@ static int snd_hrtimer_start(struct snd_timer *t)
{
struct snd_hrtimer *stime = t->private_data;
- atomic_set(&stime->running, 0);
- hrtimer_try_to_cancel(&stime->hrt);
+ if (stime->in_callback)
+ return 0;
hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
HRTIMER_MODE_REL);
- atomic_set(&stime->running, 1);
return 0;
}
static int snd_hrtimer_stop(struct snd_timer *t)
{
struct snd_hrtimer *stime = t->private_data;
- atomic_set(&stime->running, 0);
+
+ if (stime->in_callback)
+ return 0;
hrtimer_try_to_cancel(&stime->hrt);
return 0;
}