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ALSA: pcsp - Fix locking messes in snd-pcsp

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snd-pcsp driver takes chip->substream_lock together with PCM substream
lock.  These are even mixed up with hrtimer's lock, resulting in messy
lock depencies.  Right now, snd-pcsp driver resolves the deadlock by
using HRTIMER_CB_SOFTIRQ.  However, this isn't nice for a really fast
path like bit-flipping.

This patch introduces a tasklet for PCM period handling so that the
hrtimer callback can be handled fast.  This also reduce the use of
chip->substream_lock to avoid deadlocks.  It's still used in pointer
callback, but even this could be removed with a proper barrier.

Another good solution is to introduce async trigger callback.  But,
this will involve with a major rewrite of the PCM core code, so I
take first this easy fix.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2008-08-11 10:18:39 +02:00
parent 76a4d10e52
commit 96c7d478ef
3 changed files with 56 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
sound/drivers/pcsp/pcsp.c
View File

@ -96,7 +96,7 @@ static int __devinit snd_card_pcsp_probe(int devnum, struct device *dev)
return -EINVAL;
hrtimer_init(&pcsp_chip.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
pcsp_chip.timer.cb_mode = HRTIMER_CB_SOFTIRQ;
pcsp_chip.timer.cb_mode = HRTIMER_CB_IRQSAFE;
pcsp_chip.timer.function = pcsp_do_timer;
card = snd_card_new(index, id, THIS_MODULE, 0);
@ -188,10 +188,8 @@ static int __devexit pcsp_remove(struct platform_device *dev)
static void pcsp_stop_beep(struct snd_pcsp *chip)
{
spin_lock_irq(&chip->substream_lock);
if (!chip->playback_substream)
pcspkr_stop_sound();
spin_unlock_irq(&chip->substream_lock);
pcsp_sync_stop(chip);
pcspkr_stop_sound();
}
#ifdef CONFIG_PM

1
sound/drivers/pcsp/pcsp.h
View File

@ -77,6 +77,7 @@ struct snd_pcsp {
extern struct snd_pcsp pcsp_chip;
extern enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle);
extern void pcsp_sync_stop(struct snd_pcsp *chip);
extern int snd_pcsp_new_pcm(struct snd_pcsp *chip);
extern int snd_pcsp_new_mixer(struct snd_pcsp *chip);

95
sound/drivers/pcsp/pcsp_lib.c
View File

@ -8,6 +8,7 @@
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/interrupt.h>
#include <sound/pcm.h>
#include <asm/io.h>
#include "pcsp.h"
@ -19,6 +20,22 @@ MODULE_PARM_DESC(nforce_wa, "Apply NForce chipset workaround "
#define DMIX_WANTS_S16 1
/*
* Call snd_pcm_period_elapsed in a tasklet
* This avoids spinlock messes and long-running irq contexts
*/
static void pcsp_call_pcm_elapsed(unsigned long priv)
{
if (atomic_read(&pcsp_chip.timer_active)) {
struct snd_pcm_substream *substream;
substream = pcsp_chip.playback_substream;
if (substream)
snd_pcm_period_elapsed(substream);
}
}
static DECLARE_TASKLET(pcsp_pcm_tasklet, pcsp_call_pcm_elapsed, 0);
enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
{
unsigned char timer_cnt, val;
@ -28,41 +45,23 @@ enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
struct snd_pcm_substream *substream;
struct snd_pcm_runtime *runtime;
struct snd_pcsp *chip = container_of(handle, struct snd_pcsp, timer);
unsigned long flags;
if (chip->thalf) {
outb(chip->val61, 0x61);
chip->thalf = 0;
if (!atomic_read(&chip->timer_active))
return HRTIMER_NORESTART;
goto stop;
hrtimer_forward(&chip->timer, chip->timer.expires,
ktime_set(0, chip->ns_rem));
return HRTIMER_RESTART;
}
spin_lock_irq(&chip->substream_lock);
/* Takashi Iwai says regarding this extra lock:
If the irq handler handles some data on the DMA buffer, it should
do snd_pcm_stream_lock().
That protects basically against all races among PCM callbacks, yes.
However, there are two remaining issues:
1. The substream pointer you try to lock isn't protected _before_
this lock yet.
2. snd_pcm_period_elapsed() itself acquires the lock.
The requirement of another lock is because of 1. When you get
chip->playback_substream, it's not protected.
Keeping this lock while snd_pcm_period_elapsed() assures the substream
is still protected (at least, not released). And the other status is
handled properly inside snd_pcm_stream_lock() in
snd_pcm_period_elapsed().
*/
if (!chip->playback_substream)
goto exit_nr_unlock1;
substream = chip->playback_substream;
snd_pcm_stream_lock(substream);
if (!atomic_read(&chip->timer_active))
goto exit_nr_unlock2;
goto stop;
substream = chip->playback_substream;
if (!substream)
goto stop;
runtime = substream->runtime;
fmt_size = snd_pcm_format_physical_width(runtime->format) >> 3;
@ -87,6 +86,8 @@ enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
period_bytes = snd_pcm_lib_period_bytes(substream);
buffer_bytes = snd_pcm_lib_buffer_bytes(substream);
spin_lock_irqsave(&chip->substream_lock, flags);
chip->playback_ptr += PCSP_INDEX_INC() * fmt_size;
periods_elapsed = chip->playback_ptr - chip->period_ptr;
if (periods_elapsed < 0) {
@ -102,18 +103,15 @@ enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
* or ALSA will BUG on us. */
chip->playback_ptr %= buffer_bytes;
snd_pcm_stream_unlock(substream);
if (periods_elapsed) {
snd_pcm_period_elapsed(substream);
chip->period_ptr += periods_elapsed * period_bytes;
chip->period_ptr %= buffer_bytes;
tasklet_schedule(&pcsp_pcm_tasklet);
}
spin_unlock_irq(&chip->substream_lock);
spin_unlock_irqrestore(&chip->substream_lock, flags);
if (!atomic_read(&chip->timer_active))
return HRTIMER_NORESTART;
goto stop;
chip->ns_rem = PCSP_PERIOD_NS();
ns = (chip->thalf ? PCSP_CALC_NS(timer_cnt) : chip->ns_rem);
@ -121,10 +119,7 @@ enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
hrtimer_forward(&chip->timer, chip->timer.expires, ktime_set(0, ns));
return HRTIMER_RESTART;
exit_nr_unlock2:
snd_pcm_stream_unlock(substream);
exit_nr_unlock1:
spin_unlock_irq(&chip->substream_lock);
stop:
return HRTIMER_NORESTART;
}
@ -164,26 +159,35 @@ static void pcsp_stop_playing(struct snd_pcsp *chip)
spin_unlock(&i8253_lock);
}
/*
* Force to stop and sync the stream
*/
void pcsp_sync_stop(struct snd_pcsp *chip)
{
local_irq_disable();
pcsp_stop_playing(chip);
local_irq_enable();
hrtimer_cancel(&chip->timer);
tasklet_kill(&pcsp_pcm_tasklet);
}
static int snd_pcsp_playback_close(struct snd_pcm_substream *substream)
{
struct snd_pcsp *chip = snd_pcm_substream_chip(substream);
#if PCSP_DEBUG
printk(KERN_INFO "PCSP: close called\n");
#endif
if (atomic_read(&chip->timer_active)) {
printk(KERN_ERR "PCSP: timer still active\n");
pcsp_stop_playing(chip);
}
spin_lock_irq(&chip->substream_lock);
pcsp_sync_stop(chip);
chip->playback_substream = NULL;
spin_unlock_irq(&chip->substream_lock);
return 0;
}
static int snd_pcsp_playback_hw_params(struct snd_pcm_substream *substream,
struct snd_pcm_hw_params *hw_params)
{
struct snd_pcsp *chip = snd_pcm_substream_chip(substream);
int err;
pcsp_sync_stop(chip);
err = snd_pcm_lib_malloc_pages(substream,
params_buffer_bytes(hw_params));
if (err < 0)
@ -193,9 +197,11 @@ static int snd_pcsp_playback_hw_params(struct snd_pcm_substream *substream,
static int snd_pcsp_playback_hw_free(struct snd_pcm_substream *substream)
{
struct snd_pcsp *chip = snd_pcm_substream_chip(substream);
#if PCSP_DEBUG
printk(KERN_INFO "PCSP: hw_free called\n");
#endif
pcsp_sync_stop(chip);
return snd_pcm_lib_free_pages(substream);
}
@ -211,6 +217,7 @@ static int snd_pcsp_playback_prepare(struct snd_pcm_substream *substream)
snd_pcm_lib_period_bytes(substream),
substream->runtime->periods);
#endif
pcsp_sync_stop(chip);
chip->playback_ptr = 0;
chip->period_ptr = 0;
return 0;
@ -241,7 +248,11 @@ static snd_pcm_uframes_t snd_pcsp_playback_pointer(struct snd_pcm_substream
*substream)
{
struct snd_pcsp *chip = snd_pcm_substream_chip(substream);
return bytes_to_frames(substream->runtime, chip->playback_ptr);
unsigned int pos;
spin_lock(&chip->substream_lock);
pos = chip->playback_ptr;
spin_unlock(&chip->substream_lock);
return bytes_to_frames(substream->runtime, pos);
}
static struct snd_pcm_hardware snd_pcsp_playback = {
@ -278,9 +289,7 @@ static int snd_pcsp_playback_open(struct snd_pcm_substream *substream)
return -EBUSY;
}
runtime->hw = snd_pcsp_playback;
spin_lock_irq(&chip->substream_lock);
chip->playback_substream = substream;
spin_unlock_irq(&chip->substream_lock);
return 0;
}