ww-mutex: clarify help text for DEBUG_WW_MUTEX_SLOWPATH

We really don't want distro's enabling this in their kernels.  Try and
make that more clear.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

lib/Kconfig.debug

@@ -892,6 +892,10 @@ config DEBUG_WW_MUTEX_SLOWPATH
 	 the full mutex checks enabled with (CONFIG_PROVE_LOCKING) this
 	 will test all possible w/w mutex interface abuse with the
 	 exception of simply not acquiring all the required locks.
+	 Note that this feature can introduce significant overhead, so
+	 it really should not be enabled in a production or distro kernel,
+	 even a debug kernel.  If you are a driver writer, enable it.  If
+	 you are a distro, do not.
 
 config DEBUG_LOCK_ALLOC
 	bool "Lock debugging: detect incorrect freeing of live locks"