rcu/nocb: EXP Check use and usefulness of ->nocb_lock_contended

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

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 12b14d7a2cf2f367297b6cf169cdce653befea9d..97c730753a6d0d807685aebcdb33bb5276c69b7d 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1515,6 +1515,7 @@ static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
        if (raw_spin_trylock(&rdp->nocb_bypass_lock))
                return;
        atomic_inc(&rdp->nocb_lock_contended);
+       WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
        smp_mb__after_atomic(); /* atomic_inc() before lock. */
        raw_spin_lock(&rdp->nocb_bypass_lock);
        smp_mb__before_atomic(); /* atomic_dec() after lock. */
@@ -1533,7 +1534,8 @@ static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
  */
 static void rcu_nocb_wait_contended(struct rcu_data *rdp)
 {
-       while (atomic_read(&rdp->nocb_lock_contended))
+       WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
+       while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
                cpu_relax();
 }