Re: [PATCH] input: fix locking context in ml_ff_set_gain

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, Nov 02, 2009 at 09:53:58PM -0800, Arjan van de Ven wrote:
> > 
> > OK, it ended up being pretty simple. Anssi, any chance you could test
> > it to make sure I did not screw up? Thanks!
> > 
> @@ -371,35 +370,34 @@ static void ml_effect_timer(unsigned long
> timer_data) 
>  	debug("timer: updating effects");
>  
> -	spin_lock(&ml->timer_lock);
> +	spin_lock_irq(&dev->event_lock);
>  	ml_play_effects(ml);
> -	spin_unlock(&ml->timer_lock);
> +	spin_unlock_irq(&dev->event_lock);
>  }
> 
> this bit looks evil.
> 
> might be better off as irqsave...
> 

Yes, I think I better do that. _irq should work at the moment but who
knows what happen in the future...

-- 
Dmitry

Input: fix locking in memoryless force-feedback devices

From: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Now that input core acquires dev->event_lock spinlock and disables
interrupts when propagating input events, using spin_lock_bh() in
ff-memless driver is not allowed. Actually, the timer_lock itself
is not needed anymore, we should simply use dev->event_lock
as well.

Also do a small cleanup in force-feedback core.

Reported-by: kerneloops.org
Reported-by: http://www.kerneloops.org/searchweek.php?search=ml_ff_set_gain
Reported-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
---

 drivers/input/ff-core.c    |   20 +++++++++++---------
 drivers/input/ff-memless.c |   26 +++++++++++---------------
 include/linux/input.h      |    4 ++++
 3 files changed, 26 insertions(+), 24 deletions(-)


diff --git a/drivers/input/ff-core.c b/drivers/input/ff-core.c
index 72c63e5..38df81f 100644
--- a/drivers/input/ff-core.c
+++ b/drivers/input/ff-core.c
@@ -337,16 +337,16 @@ int input_ff_create(struct input_dev *dev, int max_effects)
 	dev->ff = ff;
 	dev->flush = flush_effects;
 	dev->event = input_ff_event;
-	set_bit(EV_FF, dev->evbit);
+	__set_bit(EV_FF, dev->evbit);
 
 	/* Copy "true" bits into ff device bitmap */
 	for (i = 0; i <= FF_MAX; i++)
 		if (test_bit(i, dev->ffbit))
-			set_bit(i, ff->ffbit);
+			__set_bit(i, ff->ffbit);
 
 	/* we can emulate RUMBLE with periodic effects */
 	if (test_bit(FF_PERIODIC, ff->ffbit))
-		set_bit(FF_RUMBLE, dev->ffbit);
+		__set_bit(FF_RUMBLE, dev->ffbit);
 
 	return 0;
 }
@@ -362,12 +362,14 @@ EXPORT_SYMBOL_GPL(input_ff_create);
  */
 void input_ff_destroy(struct input_dev *dev)
 {
-	clear_bit(EV_FF, dev->evbit);
-	if (dev->ff) {
-		if (dev->ff->destroy)
-			dev->ff->destroy(dev->ff);
-		kfree(dev->ff->private);
-		kfree(dev->ff);
+	struct ff_device *ff = dev->ff;
+
+	__clear_bit(EV_FF, dev->evbit);
+	if (ff) {
+		if (ff->destroy)
+			ff->destroy(ff);
+		kfree(ff->private);
+		kfree(ff);
 		dev->ff = NULL;
 	}
 }
diff --git a/drivers/input/ff-memless.c b/drivers/input/ff-memless.c
index 2d1415e..b483b29 100644
--- a/drivers/input/ff-memless.c
+++ b/drivers/input/ff-memless.c
@@ -61,7 +61,6 @@ struct ml_device {
 	struct ml_effect_state states[FF_MEMLESS_EFFECTS];
 	int gain;
 	struct timer_list timer;
-	spinlock_t timer_lock;
 	struct input_dev *dev;
 
 	int (*play_effect)(struct input_dev *dev, void *data,
@@ -368,38 +367,38 @@ static void ml_effect_timer(unsigned long timer_data)
 {
 	struct input_dev *dev = (struct input_dev *)timer_data;
 	struct ml_device *ml = dev->ff->private;
+	unsigned long flags;
 
 	debug("timer: updating effects");
 
-	spin_lock(&ml->timer_lock);
+	spin_lock_irqsave(&dev->event_lock, flags);
 	ml_play_effects(ml);
-	spin_unlock(&ml->timer_lock);
+	spin_unlock_irqrestore(&dev->event_lock, flags);
 }
 
+/*
+ * Sets requested gain for FF effects. Called with dev->event_lock held.
+ */
 static void ml_ff_set_gain(struct input_dev *dev, u16 gain)
 {
 	struct ml_device *ml = dev->ff->private;
 	int i;
 
-	spin_lock_bh(&ml->timer_lock);
-
 	ml->gain = gain;
 
 	for (i = 0; i < FF_MEMLESS_EFFECTS; i++)
 		__clear_bit(FF_EFFECT_PLAYING, &ml->states[i].flags);
 
 	ml_play_effects(ml);
-
-	spin_unlock_bh(&ml->timer_lock);
 }
 
+/*
+ * Start/stop specified FF effect. Called with dev->event_lock held.
+ */
 static int ml_ff_playback(struct input_dev *dev, int effect_id, int value)
 {
 	struct ml_device *ml = dev->ff->private;
 	struct ml_effect_state *state = &ml->states[effect_id];
-	unsigned long flags;
-
-	spin_lock_irqsave(&ml->timer_lock, flags);
 
 	if (value > 0) {
 		debug("initiated play");
@@ -425,8 +424,6 @@ static int ml_ff_playback(struct input_dev *dev, int effect_id, int value)
 		ml_play_effects(ml);
 	}
 
-	spin_unlock_irqrestore(&ml->timer_lock, flags);
-
 	return 0;
 }
 
@@ -436,7 +433,7 @@ static int ml_ff_upload(struct input_dev *dev,
 	struct ml_device *ml = dev->ff->private;
 	struct ml_effect_state *state = &ml->states[effect->id];
 
-	spin_lock_bh(&ml->timer_lock);
+	spin_lock_irq(&dev->event_lock);
 
 	if (test_bit(FF_EFFECT_STARTED, &state->flags)) {
 		__clear_bit(FF_EFFECT_PLAYING, &state->flags);
@@ -448,7 +445,7 @@ static int ml_ff_upload(struct input_dev *dev,
 		ml_schedule_timer(ml);
 	}
 
-	spin_unlock_bh(&ml->timer_lock);
+	spin_unlock_irq(&dev->event_lock);
 
 	return 0;
 }
@@ -482,7 +479,6 @@ int input_ff_create_memless(struct input_dev *dev, void *data,
 	ml->private = data;
 	ml->play_effect = play_effect;
 	ml->gain = 0xffff;
-	spin_lock_init(&ml->timer_lock);
 	setup_timer(&ml->timer, ml_effect_timer, (unsigned long)dev);
 
 	set_bit(FF_GAIN, dev->ffbit);
diff --git a/include/linux/input.h b/include/linux/input.h
index 0ccfc30..c2b1a7d 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -1377,6 +1377,10 @@ extern struct class input_class;
  * methods; erase() is optional. set_gain() and set_autocenter() need
  * only be implemented if driver sets up FF_GAIN and FF_AUTOCENTER
  * bits.
+ *
+ * Note that playback(), set_gain() and set_autocenter() are called with
+ * dev->event_lock spinlock held and interrupts off and thus may not
+ * sleep.
  */
 struct ff_device {
 	int (*upload)(struct input_dev *dev, struct ff_effect *effect,