From: Manfred Spraul <manfred@colorfullife.com>

The mwave driver uses a user space daemon for some modem operations. The
user space daemon calls ioctl(,IOCTL_MW_GET_IPC), and the driver returns
after an interrupt arrived. The actual wait used
interruptible_sleep_on(), which can lead to lost wakeups. A local 
spinlock on the stack is used to close that race, but this is broken on 
SMP, perhaps even with preempt.

The attached patch fixes that by switching to the normal 
add_wait_queue/test_if_race_occured/schedule/remove_wait_queue sequence.