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>

2 files changed, 6 insertions, 2 deletions

diff --git a/sound/usb/card.c b/sound/usb/card.c
index e769d3977716..c3b5b7dca1c3 100644
--- a/sound/usb/card.c
+++ b/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;
 }
 
diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index 25c4c7e217de..91d0380431b4 100644
--- a/sound/usb/usbaudio.h
+++ b/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 */