rcu: Add preemptibility checks in rcu_sched_qs() and rcu_bh_qs()

This commit adds WARN_ON_ONCE() calls that trigger if either
rcu_sched_qs() or rcu_bh_qs() are invoked with preemption enabled.
In the immortal words of Peter Zijlstra: "these are much harder to ignore
than comments".

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

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3bee58fc23b1..b01a02e7a0b7 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -250,6 +250,7 @@ static int rcu_gp_in_progress(struct rcu_state *rsp)
  */
 void rcu_sched_qs(void)
 {
+        RCU_LOCKDEP_WARN(preemptible(), "rcu_sched_qs() invoked with preemption enabled!!!");
         if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
                 return;
         trace_rcu_grace_period(TPS("rcu_sched"),
@@ -265,6 +266,7 @@ void rcu_sched_qs(void)
 
 void rcu_bh_qs(void)
 {
+        RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!");
         if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
                 trace_rcu_grace_period(TPS("rcu_bh"),
                                        __this_cpu_read(rcu_bh_data.gpnum),