[PATCH] Fix locking problem between em28xx and em28xx-dvb modules

[Chris Rankin <rankincj@yahoo.com>]

[-- Attachment #1: Type: text/plain, Size: 778 bytes --]

Hi,

I've thought about this patch a bit more overnight, and it occurred to me that 
while  em28xx_init_extension() now takes the device mutex followed by the device 
list mutex, my original fix would have had em28xx_register_extension() taking 
the device list mutex followed by the device mutex. And that sounds suspiciously 
like a potential deadlock to me. So I was wondering: does 
em28xx_register_extension() actually need to lock the device if the device list 
has already been locked?

I've also moved two printk()s outside the region where we hold the device list 
mutex, because locked bits should be as brief as possible and neither printk() 
does anything that needs the lock.

A new patch is attached, for review.

Signed-off-by: Chris Rankin <rankincj@yahoo.com>


[-- Attachment #2: EM28xx-DVB.diff --]
[-- Type: text/x-patch, Size: 1424 bytes --]

--- linux-3.0/drivers/media/video/em28xx/em28xx-core.c.orig	2011-08-16 09:15:46.000000000 +0100
+++ linux-3.0/drivers/media/video/em28xx/em28xx-core.c	2011-08-16 09:21:08.000000000 +0100
@@ -1193,8 +1193,8 @@
 	list_for_each_entry(dev, &em28xx_devlist, devlist) {
 		ops->init(dev);
 	}
-	printk(KERN_INFO "Em28xx: Initialized (%s) extension\n", ops->name);
 	mutex_unlock(&em28xx_devlist_mutex);
+	printk(KERN_INFO "Em28xx: Initialized (%s) extension\n", ops->name);
 	return 0;
 }
 EXPORT_SYMBOL(em28xx_register_extension);
@@ -1207,9 +1207,9 @@
 	list_for_each_entry(dev, &em28xx_devlist, devlist) {
 		ops->fini(dev);
 	}
-	printk(KERN_INFO "Em28xx: Removed (%s) extension\n", ops->name);
 	list_del(&ops->next);
 	mutex_unlock(&em28xx_devlist_mutex);
+	printk(KERN_INFO "Em28xx: Removed (%s) extension\n", ops->name);
 }
 EXPORT_SYMBOL(em28xx_unregister_extension);
 
--- linux-3.0/drivers/media/video/em28xx/em28xx-dvb.c.orig	2011-08-16 09:16:03.000000000 +0100
+++ linux-3.0/drivers/media/video/em28xx/em28xx-dvb.c	2011-08-16 09:17:06.000000000 +0100
@@ -542,7 +542,6 @@
 	dev->dvb = dvb;
 	dvb->fe[0] = dvb->fe[1] = NULL;
 
-	mutex_lock(&dev->lock);
 	em28xx_set_mode(dev, EM28XX_DIGITAL_MODE);
 	/* init frontend */
 	switch (dev->model) {
@@ -711,7 +710,6 @@
 	em28xx_info("Successfully loaded em28xx-dvb\n");
 ret:
 	em28xx_set_mode(dev, EM28XX_SUSPEND);
-	mutex_unlock(&dev->lock);
 	return result;
 
 out_free: