rcu: Check for idle-loop entry while in RCU read-side critical section

The inner idle loop is an extended quiescent state for all flavors
of RCU, but there have been recent bug involving use of RCU read-side
primitives from within the idle loop.  Therefore, this commit enlists
lockdep-RCU to detect attempts to enter the inner idle loop while in
an RCU read-side critical section, emitting a lockdep-RCU splat if so.

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

1 files changed, 11 insertions, 0 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0569ba11e35a..195bf1fb59ea 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -366,6 +366,17 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
         atomic_inc(&rdtp->dynticks);
         smp_mb__after_atomic_inc();  /* Force ordering with next sojourn. */
         WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+
+        /*
+         * The idle task is not permitted to enter the idle loop while
+         * in an RCU read-side critical section.
+         */
+        rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
+                           "Illegal idle entry in RCU read-side critical section.");
+        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
+                           "Illegal idle entry in RCU-bh read-side critical section.");
+        rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
+                           "Illegal idle entry in RCU-sched read-side critical section.");
 }
 
 /**