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/rcutiny.c b/kernel/rcutiny.c
index 977296dca0a4..8e00d461911e 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -319,6 +319,10 @@ static void rcu_process_callbacks(struct softirq_action *unused)
  */
 void synchronize_sched(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_sched() in RCU read-side critical section");
         cond_resched();
 }
 EXPORT_SYMBOL_GPL(synchronize_sched);