From: Neil Horman <nhorman@tuxdriver.com>
Date: Tue, 30 Apr 2013 11:35:05 -0400

Bart Van Assche recently reported a warning to me:

 ...

This resulted from my commit ca99ca14c which introduced a mutex_trylock
operation in a path that could execute in interrupt context.  When mutex
debugging is enabled, the above warns the user when we are in fact
exectuting in interrupt context
interrupt context.

After some discussion, It seems that a semaphore is the proper mechanism to use
here.  While mutexes are defined to be unusable in interrupt context, no such
condition exists for semaphores (save for the fact that the non blocking api
calls, like up and down_trylock must be used when in irq context).

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Reported-by: Bart Van Assche <bvanassche@acm.org>

Neil this looks good to me so I'm going to toss it into my tree and queue
it up for -stable too, thanks!