ALSA: jack: Fix mutex call in snd_jack_report()

snd_jack_report() is supposed to be callable from an IRQ context, too,
and it's indeed used in that way from virtsnd driver.  The fix for
input_dev race in commit 1b6a6fc ("ALSA: jack: Access input_dev
under mutex"), however, introduced a mutex lock in snd_jack_report(),
and this resulted in a potential sleep-in-atomic.

For addressing that problem, this patch changes the relevant code to
use the object get/put and removes the mutex usage.  That is,
snd_jack_report(), it takes input_get_device() and leaves with
input_put_device() for assuring the input_dev being assigned.

Although the whole mutex could be reduced, we keep it because it can
be still a protection for potential races between creation and
deletion.

Fixes: 1b6a6fc ("ALSA: jack: Access input_dev under mutex")
Reported-by: Dan Carpenter <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]
Tested-by: Amadeusz Sławiński <[email protected]>
Cc: <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>

Author: tiwai

sound/core/jack.c

@@ -654,6 +654,7 @@ void snd_jack_report(struct snd_jack *jack, int status)
 	struct snd_jack_kctl *jack_kctl;
 	unsigned int mask_bits = 0;
 #ifdef CONFIG_SND_JACK_INPUT_DEV
+	struct input_dev *idev;
 	int i;
 #endif
 
@@ -670,31 +671,29 @@ void snd_jack_report(struct snd_jack *jack, int status)
 					     status & jack_kctl->mask_bits);
 
 #ifdef CONFIG_SND_JACK_INPUT_DEV
-	mutex_lock(&jack->input_dev_lock);
-	if (!jack->input_dev) {
-		mutex_unlock(&jack->input_dev_lock);
+	idev = input_get_device(jack->input_dev);
+	if (!idev)
 		return;
-	}
 
 	for (i = 0; i < ARRAY_SIZE(jack->key); i++) {
 		int testbit = ((SND_JACK_BTN_0 >> i) & ~mask_bits);
 
 		if (jack->type & testbit)
-			input_report_key(jack->input_dev, jack->key[i],
+			input_report_key(idev, jack->key[i],
 					 status & testbit);
 	}
 
 	for (i = 0; i < ARRAY_SIZE(jack_switch_types); i++) {
 		int testbit = ((1 << i) & ~mask_bits);
 
 		if (jack->type & testbit)
-			input_report_switch(jack->input_dev,
+			input_report_switch(idev,
 					    jack_switch_types[i],
 					    status & testbit);
 	}
 
-	input_sync(jack->input_dev);
-	mutex_unlock(&jack->input_dev_lock);
+	input_sync(idev);
+	input_put_device(idev);
 #endif /* CONFIG_SND_JACK_INPUT_DEV */
 }
 EXPORT_SYMBOL(snd_jack_report);