The powerpc page table freeing relies on the fact that IRQs hold off
an RCU grace period, this is currently true for all existing RCU
implementations but is not an assumption Paul wants to support.
Therefore, also take the RCU read lock along with disabling IRQs to
ensure the RCU grace period does at least cover these lookups.
Requested-by: Paul E. McKenney<paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra<a.p.zijlstra@xxxxxxxxx>
Cc: Nick Piggin<npiggin@xxxxxxx>
Cc: Benjamin Herrenschmidt<benh@xxxxxxxxxxxxxxxxxxx>