linux-kernel - [PATCH 3/7] [media] cx88: hold device lock during sub-driver initialization

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Date:	Mon, 4 Apr 2011 22:27:13 -0500
From:	Jonathan Nieder <jrnieder@...il.com>
To:	linux-media@...r.kernel.org
Cc:	Huber Andreas <hobrom@...ax.at>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Hans Verkuil <hverkuil@...all.nl>,
	linux-kernel@...r.kernel.org, Ben Hutchings <ben@...adent.org.uk>,
	Steven Toth <stoth@...nellabs.com>
Subject: [PATCH 3/7] [media] cx88: hold device lock during sub-driver
 initialization

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>
Signed-off-by: Jonathan Nieder <jrnieder@...il.com>
---
 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(-)

diff --git a/drivers/media/video/cx88/cx88-blackbird.c b/drivers/media/video/cx88/cx88-blackbird.c
index a6f7d53..f637d34 100644
--- 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 cx8802_driver *drv)
 	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;
 
diff --git a/drivers/media/video/cx88/cx88-mpeg.c b/drivers/media/video/cx88/cx88-mpeg.c
index 9147c16..497f26f 100644
--- 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_driver *drv)
 		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;
diff --git a/drivers/media/video/cx88/cx88.h b/drivers/media/video/cx88/cx88.h
index 9731daa..3d32f4a 100644
--- 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);
 
+	/* Callers to the following functions must hold core->lock */
+
 	/* 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 */
-
 	int (*remove)(struct cx8802_driver *drv);
 
 	/* MPEG 8802 -> mini driver - Access for hardware control */
-- 
1.7.5.rc0

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