linux-kernel - [126/165] [media] cx88: hold device lock during sub-driver

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Message-Id: <20110601081205.946401126@blue.kroah.org>
Date:	Wed, 01 Jun 2011 17:11:36 +0900
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Jonathan Nieder <jrnieder@...il.com>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [126/165] [media] cx88: hold device lock during sub-driver

2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------
 initialization
Content-Length: 2838
Lines: 83

From: Jonathan Nieder <jrnieder@...il.com>

commit 1d6213ab995c61f7d1d81cf6cf876acf15d6e714 upstream.

cx8802_blackbird_probe makes a device node for the mpeg sub-device
before it has been added to dev->drvlist.  If the device is opened
during that time, the open succeeds but request_acquire cannot be
called, so the reference count remains zero.  Later, when the device
is closed, the reference count becomes negative --- uh oh.

Close the race by holding core->lock during probe and not releasing
until the device is in drvlist and initialization finished.
Previously the BKL prevented this race.

Reported-by: Andreas Huber <hobrom@....at>
Tested-by: Andi Huber <hobrom@....at>
Tested-by: Marlon de Boer <marlon@...es.nl>
Signed-off-by: Jonathan Nieder <jrnieder@...il.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/media/video/cx88/cx88-blackbird.c |    2 --
 drivers/media/video/cx88/cx88-mpeg.c      |    5 ++---
 drivers/media/video/cx88/cx88.h           |    7 ++-----
 3 files changed, 4 insertions(+), 10 deletions(-)

--- a/drivers/media/video/cx88/cx88-blackbird.c
+++ b/drivers/media/video/cx88/cx88-blackbird.c
@@ -1335,11 +1335,9 @@ static int cx8802_blackbird_probe(struct
 	blackbird_register_video(dev);
 
 	/* initial device configuration: needed ? */
-	mutex_lock(&dev->core->lock);
 //	init_controls(core);
 	cx88_set_tvnorm(core,core->tvnorm);
 	cx88_video_mux(core,0);
-	mutex_unlock(&dev->core->lock);
 
 	return 0;
 
--- a/drivers/media/video/cx88/cx88-mpeg.c
+++ b/drivers/media/video/cx88/cx88-mpeg.c
@@ -709,18 +709,17 @@ int cx8802_register_driver(struct cx8802
 		drv->request_release = cx8802_request_release;
 		memcpy(driver, drv, sizeof(*driver));
 
+		mutex_lock(&drv->core->lock);
 		err = drv->probe(driver);
 		if (err == 0) {
 			i++;
-			mutex_lock(&drv->core->lock);
 			list_add_tail(&driver->drvlist, &dev->drvlist);
-			mutex_unlock(&drv->core->lock);
 		} else {
 			printk(KERN_ERR
 			       "%s/2: cx8802 probe failed, err = %d\n",
 			       dev->core->name, err);
 		}
-
+		mutex_unlock(&drv->core->lock);
 	}
 
 	return i ? 0 : -ENODEV;
--- a/drivers/media/video/cx88/cx88.h
+++ b/drivers/media/video/cx88/cx88.h
@@ -505,13 +505,10 @@ struct cx8802_driver {
 	int (*suspend)(struct pci_dev *pci_dev, pm_message_t state);
 	int (*resume)(struct pci_dev *pci_dev);
 
-	/* MPEG 8802 -> mini driver - Driver probe and configuration */
-
-	/* Caller must _not_ hold core->lock */
-	int (*probe)(struct cx8802_driver *drv);
-
 	/* Callers to the following functions must hold core->lock */
 
+	/* MPEG 8802 -> mini driver - Driver probe and configuration */
+	int (*probe)(struct cx8802_driver *drv);
 	int (*remove)(struct cx8802_driver *drv);
 
 	/* MPEG 8802 -> mini driver - Access for hardware control */


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