Possible cause of replug lockup in em28xx-dvb

[Chris Rankin <rankincj@yahoo.com>]

Hi,

I've been "plugging away" at the locking issue in the em28xx / em28xx-dvb 
modules, and I think I've found the reason. Basically, we're trying to acquire 
the dev->lock mutex again in dvb_init() when we've already acquired it in 
em28xx_init_dev().

The exact sequence is:
	em28xx_init_dev()
	- em28xx_init_extension()
	-- ops->init(dev) function for each extension

where ops->init = dvb_init() for the em28xx-dvb extension. However, if you 
remove the em28xx-dvb module first then the em28xx_extension_devlist is empty
and you avoid calling dvb_init().

As to the fix, I'm thinking of moving the mutex_lock() / mutex_unlock() calls
from dvb_init() to em28xx_register_extension() instead. This way, we ensure that 
dvb_init() is still always called with the dvb->lock mutex held.

I'll submit a patch for review in the morning. (Or should I say, "later this 
morning"...)

Cheers,
Chris