ALSA: pcsp - Fix locking messes in snd-pcsp

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>

3 files changed, 56 insertions, 48 deletions

diff --git a/sound/drivers/pcsp/pcsp.c b/sound/drivers/pcsp/pcsp.c
index 1899cf0685bc..87219bf0a35e 100644
--- a/sound/drivers/pcsp/pcsp.c
+++ b/sound/drivers/pcsp/pcsp.c
@@ -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
diff --git a/sound/drivers/pcsp/pcsp.h b/sound/drivers/pcsp/pcsp.h
index 1d661f795e8c..70533a333b5b 100644
--- a/sound/drivers/pcsp/pcsp.h
+++ b/sound/drivers/pcsp/pcsp.h
@@ -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);
diff --git a/sound/drivers/pcsp/pcsp_lib.c b/sound/drivers/pcsp/pcsp_lib.c
index e341f3f83b6a..40f95f549d2b 100644
--- a/sound/drivers/pcsp/pcsp_lib.c
+++ b/sound/drivers/pcsp/pcsp_lib.c
@@ -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;
 }