[patch] snd-pcsp: use HRTIMER_CB_SOFTIRQ

From: Stas Sergeev
Date: Mon May 19 2008 - 12:38:04 EST


Change HRTIMER_CB_IRQSAFE to HRTIMER_CB_SOFTIRQ,
as suggested by Thomas Gleixner.
That solves the lock dependancy reported in
Bug #10701.
That also allows to call hrtimer_start()
directly, tasklet "stupid hack" removed.

Signed-off-by: Stas Sergeev <stsp@xxxxxxxx>
diff --git a/sound/drivers/pcsp/pcsp.c b/sound/drivers/pcsp/pcsp.c
index 54a1f90..1899cf0 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_IRQSAFE;
+ pcsp_chip.timer.cb_mode = HRTIMER_CB_SOFTIRQ;
pcsp_chip.timer.function = pcsp_do_timer;

card = snd_card_new(index, id, THIS_MODULE, 0);
diff --git a/sound/drivers/pcsp/pcsp_lib.c b/sound/drivers/pcsp/pcsp_lib.c
index ac6238e..c30820d 100644
--- a/sound/drivers/pcsp/pcsp_lib.c
+++ b/sound/drivers/pcsp/pcsp_lib.c
@@ -9,7 +9,6 @@
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <sound/pcm.h>
-#include <linux/interrupt.h>
#include <asm/io.h>
#include "pcsp.h"

@@ -18,34 +17,8 @@ module_param(nforce_wa, bool, 0444);
MODULE_PARM_DESC(nforce_wa, "Apply NForce chipset workaround "
"(expect bad sound)");

-static void pcsp_start_timer(unsigned long dummy)
-{
- hrtimer_start(&pcsp_chip.timer, ktime_set(0, 0), HRTIMER_MODE_REL);
-}
-
-/*
- * We need the hrtimer_start as a tasklet to avoid
- * the nasty locking problem. :(
- * The problem:
- * - The timer handler is called with the cpu_base->lock
- * already held by hrtimer code.
- * - snd_pcm_period_elapsed() takes the
- * substream->self_group.lock.
- * So far so good.
- * But the snd_pcsp_trigger() is called with the
- * substream->self_group.lock held, and it calls
- * hrtimer_start(), which takes the cpu_base->lock.
- * You see the problem. We have the code pathes
- * which take two locks in a reverse order. This
- * can deadlock and the lock validator complains.
- * The only solution I could find was to move the
- * hrtimer_start() into a tasklet. -stsp
- */
-static DECLARE_TASKLET(pcsp_start_timer_tasklet, pcsp_start_timer, 0);
-
enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
{
- unsigned long flags;
unsigned char timer_cnt, val;
int periods_elapsed;
u64 ns;
@@ -64,9 +37,7 @@ enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
return HRTIMER_RESTART;
}

- /* hrtimer calls us from both hardirq and softirq contexts,
- * so irqsave :( */
- spin_lock_irqsave(&chip->substream_lock, flags);
+ 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
@@ -132,7 +105,7 @@ enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
chip->period_ptr %= buffer_bytes;
}

- spin_unlock_irqrestore(&chip->substream_lock, flags);
+ spin_unlock_irq(&chip->substream_lock);

if (!atomic_read(&chip->timer_active))
return HRTIMER_NORESTART;
@@ -146,7 +119,7 @@ enum hrtimer_restart pcsp_do_timer(struct hrtimer *handle)
exit_nr_unlock2:
snd_pcm_stream_unlock(substream);
exit_nr_unlock1:
- spin_unlock_irqrestore(&chip->substream_lock, flags);
+ spin_unlock_irq(&chip->substream_lock);
return HRTIMER_NORESTART;
}

@@ -167,7 +140,7 @@ static void pcsp_start_playing(struct snd_pcsp *chip)
atomic_set(&chip->timer_active, 1);
chip->thalf = 0;

- tasklet_schedule(&pcsp_start_timer_tasklet);
+ hrtimer_start(&pcsp_chip.timer, ktime_set(0, 0), HRTIMER_MODE_REL);
}

static void pcsp_stop_playing(struct snd_pcsp *chip)