tree 3b60a7b97e849bd68573db48dd8608cb43f05694
parent c71e56a376e4a32c19b4f401b399e9183cdcd657
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1437344020 -0700
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1437440126 -0700

rcu: Silence lockdep false positive for expedited grace periods

In a CONFIG_PREEMPT=y kernel, synchronize_rcu_expedited()
acquires the ->exp_funnel_mutex in rcu_preempt_state, then invokes
synchronize_sched_expedited, which acquires the ->exp_funnel_mutex in
rcu_sched_state.  There can be no deadlock because rcu_preempt_state
->exp_funnel_mutex acquisition always precedes that of rcu_sched_state.
But lockdep does not know that, so it gives false-positive splats.

This commit therefore associates a separate lock_class_key structure
with the rcu_sched_state structure's ->exp_funnel_mutex, allowing
lockdep to see the lock ordering, avoiding the false positives.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>