linux-kernel - [PATCH 3.12 020/123] ALSA: usb-audio: Fix deadlocks at resuming

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Date:	Tue,  4 Aug 2015 16:39:24 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Takashi Iwai <tiwai@...e.de>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 020/123] ALSA: usb-audio: Fix deadlocks at resuming

From: Takashi Iwai <tiwai@...e.de>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 1ee23fe07ee83a38ecee927e701f762888ada942 upstream.

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@...il.com>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 sound/usb/card.c     | 7 +++++--
 sound/usb/usbaudio.h | 1 +
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/sound/usb/card.c b/sound/usb/card.c
index ca55e033cf9d..bc5795f342a7 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -661,7 +661,7 @@ 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);
@@ -673,7 +673,7 @@ 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);
 }
@@ -722,6 +722,8 @@ 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
@@ -737,6 +739,7 @@ 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 caabe9b3af49..58d4ef14ff31 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 */
 	
-- 
2.5.0

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