rcu: Add lockdep-RCU checks for simple self-deadlock

It is illegal to have a grace period within a same-flavor RCU read-side
critical section, so this commit adds lockdep-RCU checks to splat when
such abuse is encountered.  This commit does not detect more elaborate
RCU deadlock situations.  These situations might be a job for lockdep
enhancements.

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

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 8bb35d73e1f9..3680b6b35bf3 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -688,6 +688,10 @@ EXPORT_SYMBOL_GPL(call_rcu);
  */
 void synchronize_rcu(void)
 {
+        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
+                           !lock_is_held(&rcu_lock_map) &&
+                           !lock_is_held(&rcu_sched_lock_map),
+                           "Illegal synchronize_rcu() in RCU read-side critical section");
         if (!rcu_scheduler_active)
                 return;
         wait_rcu_gp(call_rcu);