ALSA: usb-audio: Fix deadlocks at resuming

The recent addition of the USB audio mixer suspend/resume may lead to
deadlocks when the driver tries to call usb_autopm_get_interface()
recursively, since the function tries to sync with the finish of the
other calls.  For avoiding it, introduce a flag indicating the resume
operation and avoids the recursive usb_autopm_get_interface() calls
during the resume.

Reported-and-tested-by: Bryan Quigley <gquigs@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/card.c

@@ -651,7 +651,7 @@ int snd_usb_autoresume(struct snd_usb_audio *chip)
 	int err = -ENODEV;
 
 	down_read(&chip->shutdown_rwsem);
-	if (chip->probing)
+	if (chip->probing && chip->in_pm)
 		err = 0;
 	else if (!chip->shutdown)
 		err = usb_autopm_get_interface(chip->pm_intf);
@@ -663,7 +663,7 @@ int snd_usb_autoresume(struct snd_usb_audio *chip)
 void snd_usb_autosuspend(struct snd_usb_audio *chip)
 {
 	down_read(&chip->shutdown_rwsem);
-	if (!chip->shutdown && !chip->probing)
+	if (!chip->shutdown && !chip->probing && !chip->in_pm)
 		usb_autopm_put_interface(chip->pm_intf);
 	up_read(&chip->shutdown_rwsem);
 }
@@ -712,6 +712,8 @@ static int __usb_audio_resume(struct usb_interface *intf, bool reset_resume)
 		return 0;
 	if (--chip->num_suspended_intf)
 		return 0;
+
+	chip->in_pm = 1;
 	/*
 	 * ALSA leaves material resumption to user space
 	 * we just notify and restart the mixers
@@ -727,6 +729,7 @@ static int __usb_audio_resume(struct usb_interface *intf, bool reset_resume)
 	chip->autosuspended = 0;
 
 err_out:
+	chip->in_pm = 0;
 	return err;
 }
 

sound/usb/usbaudio.h

@@ -40,6 +40,7 @@ struct snd_usb_audio {
 	struct rw_semaphore shutdown_rwsem;
 	unsigned int shutdown:1;
 	unsigned int probing:1;
+	unsigned int in_pm:1;
 	unsigned int autosuspended:1;	
 	unsigned int txfr_quirk:1; /* Subframe boundaries on transfers */