staging: ion: Avoid using rt_mutexes directly
RT_MUTEXES can be configured out of the kernel, causing compile
problems with ION.
To quote Colin:
"rt_mutexes were added with the deferred freeing feature. Heaps need
to return zeroed memory to userspace, but zeroing the memory on every
allocation was causing performance issues. We added a SCHED_IDLE
thread to zero memory in the background after freeing, but locking the
heap from the SCHED_IDLE thread might block a high priority allocation
thread for a long time.
The lock is only used to protect the heap's free_list and
free_list_size members, and is not held for any long or sleeping
operations. Converting to a spinlock should prevent priority
inversion without using the rt_mutex. I'd also rename it to free_lock
to so it doesn't get used as a general heap lock."
Thus this patch converts the rt_mutex usage to a spinlock and
renames the lock free_lock to be more clear as to its use.
I also had to change a bit of logic in ion_heap_freelist_drain()
to safely avoid list corruption.
Acked-by: Colin Cross <ccross@android.com>
Cc: Android Kernel Team <kernel-team@android.com>
Reported-by: Jim Davis <jim.epost@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>