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>

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 977296d..8e00d46 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c

@@ -319,6 +319,10 @@
  */
 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);

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 9cb1ae4..4b90540 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h

@@ -706,6 +706,11 @@
  */
 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");
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	if (!rcu_scheduler_active)
 		return;

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6c4a672..3cf713a 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c

@@ -1816,6 +1816,10 @@
  */
 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-sched read-side critical section");
 	if (rcu_blocking_is_gp())
 		return;
 	wait_rcu_gp(call_rcu_sched);
@@ -1833,6 +1837,10 @@
  */
 void synchronize_rcu_bh(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_bh() in RCU-bh read-side critical section");
 	if (rcu_blocking_is_gp())
 		return;
 	wait_rcu_gp(call_rcu_bh);

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 8bb35d7..3680b6b 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h

@@ -688,6 +688,10 @@
  */
 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);

diff --git a/kernel/srcu.c b/kernel/srcu.c
index 0febf61..3f99fa0 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c

@@ -172,6 +172,12 @@
 {
 	int idx;
 
+	rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
+			   !lock_is_held(&rcu_bh_lock_map) &&
+			   !lock_is_held(&rcu_lock_map) &&
+			   !lock_is_held(&rcu_sched_lock_map),
+			   "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
+
 	idx = sp->completed;
 	mutex_lock(&sp->mutex);