rcu/nocb: Introduce RCU_NOCB_LOCKDEP_WARN()

Checking for races against concurrent (de-)offloading implies the
creation of !CONFIG_RCU_NOCB_CPU stubs to check if each relevant lock
is held. For now this only implies the nocb_lock but more are to be
expected.

Create instead a NOCB specific version of RCU_LOCKDEP_WARN() to avoid
the proliferation of stubs.

Signed-off-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Paul E. McKenney <[email protected]>
Signed-off-by: Neeraj Upadhyay <[email protected]>

Author: Frederic Weisbecker

include/linux/rcupdate.h

@@ -144,11 +144,18 @@ void rcu_init_nohz(void);
 int rcu_nocb_cpu_offload(int cpu);
 int rcu_nocb_cpu_deoffload(int cpu);
 void rcu_nocb_flush_deferred_wakeup(void);
+
+#define RCU_NOCB_LOCKDEP_WARN(c, s) RCU_LOCKDEP_WARN(c, s)
+
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
+
 static inline void rcu_init_nohz(void) { }
 static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
 static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
 static inline void rcu_nocb_flush_deferred_wakeup(void) { }
+
+#define RCU_NOCB_LOCKDEP_WARN(c, s)
+
 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
 
 /*

kernel/rcu/tree_nocb.h

@@ -16,10 +16,6 @@
 #ifdef CONFIG_RCU_NOCB_CPU
 static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
 static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */
-static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp)
-{
-	return lockdep_is_held(&rdp->nocb_lock);
-}
 
 static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
 {
@@ -1653,16 +1649,6 @@ static void show_rcu_nocb_state(struct rcu_data *rdp)
 
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 
-static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp)
-{
-	return 0;
-}
-
-static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
-{
-	return false;
-}
-
 /* No ->nocb_lock to acquire.  */
 static void rcu_nocb_lock(struct rcu_data *rdp)
 {

kernel/rcu/tree_plugin.h

@@ -24,10 +24,10 @@ static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
 	 * timers have their own means of synchronization against the
 	 * offloaded state updaters.
 	 */
-	RCU_LOCKDEP_WARN(
+	RCU_NOCB_LOCKDEP_WARN(
 		!(lockdep_is_held(&rcu_state.barrier_mutex) ||
 		  (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
-		  rcu_lockdep_is_held_nocb(rdp) ||
+		  lockdep_is_held(&rdp->nocb_lock) ||
 		  (!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible()) &&
 		   rdp == this_cpu_ptr(&rcu_data)) ||
 		  rcu_current_is_nocb_kthread(rdp)),