linux/sound/core/hrtimer.c
Takashi Iwai d2c5cf88d5 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>
2016-04-26 09:34:40 +02:00

183 lines
4.2 KiB
C

/*
* ALSA timer back-end using hrtimer
* Copyright (C) 2008 Takashi Iwai
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/hrtimer.h>
#include <sound/core.h>
#include <sound/timer.h>
MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
MODULE_DESCRIPTION("ALSA hrtimer backend");
MODULE_LICENSE("GPL");
MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
#define NANO_SEC 1000000000UL /* 10^9 in sec */
static unsigned int resolution;
struct snd_hrtimer {
struct snd_timer *timer;
struct hrtimer hrt;
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;
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;
}
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 = 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;
t->private_data = stime;
return 0;
}
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;
}
return 0;
}
static int snd_hrtimer_start(struct snd_timer *t)
{
struct snd_hrtimer *stime = t->private_data;
if (stime->in_callback)
return 0;
hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
HRTIMER_MODE_REL);
return 0;
}
static int snd_hrtimer_stop(struct snd_timer *t)
{
struct snd_hrtimer *stime = t->private_data;
if (stime->in_callback)
return 0;
hrtimer_try_to_cancel(&stime->hrt);
return 0;
}
static struct snd_timer_hardware hrtimer_hw = {
.flags = SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_TASKLET,
.open = snd_hrtimer_open,
.close = snd_hrtimer_close,
.start = snd_hrtimer_start,
.stop = snd_hrtimer_stop,
};
/*
* entry functions
*/
static struct snd_timer *mytimer;
static int __init snd_hrtimer_init(void)
{
struct snd_timer *timer;
int err;
resolution = hrtimer_resolution;
/* Create a new timer and set up the fields */
err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
&timer);
if (err < 0)
return err;
timer->module = THIS_MODULE;
strcpy(timer->name, "HR timer");
timer->hw = hrtimer_hw;
timer->hw.resolution = resolution;
timer->hw.ticks = NANO_SEC / resolution;
err = snd_timer_global_register(timer);
if (err < 0) {
snd_timer_global_free(timer);
return err;
}
mytimer = timer; /* remember this */
return 0;
}
static void __exit snd_hrtimer_exit(void)
{
if (mytimer) {
snd_timer_global_free(mytimer);
mytimer = NULL;
}
}
module_init(snd_hrtimer_init);
module_exit(snd_hrtimer_exit);