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@xxxxxxxxx>
--- 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:
