[RFC 1/6] rcu: Add support for consolidated-RCU reader checking

["Joel Fernandes (Google)" <joel@joelfernandes.org>]

This patch adds support for checking RCU reader sections in list
traversal macros. Optionally, if the list macro is called under SRCU or
other lock/mutex protection, then appropriate lockdep expressions can be
passed to make the checks pass.

Existing list_for_each_entry_rcu() invocations don't need to pass the
optional fourth argument (cond) unless they are under some non-RCU
protection and needs to make lockdep check pass.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 include/linux/rculist.h  | 40 ++++++++++++++++++++++++++++++++++++----
 include/linux/rcupdate.h |  7 +++++++
 kernel/rcu/update.c      | 26 ++++++++++++++++++++++++++
 3 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index e91ec9ddcd30..b641fdd9f1a2 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -40,6 +40,25 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
  */
 #define list_next_rcu(list)	(*((struct list_head __rcu **)(&(list)->next)))
 
+/*
+ * Check during list traversal that we are within an RCU reader
+ */
+#define __list_check_rcu()						\
+	RCU_LOCKDEP_WARN(!rcu_read_lock_any_held(),			\
+			 "RCU-list traversed in non-reader section!")
+
+static inline void __list_check_rcu_cond(int dummy, ...)
+{
+	va_list ap;
+	int cond;
+
+	va_start(ap, dummy);
+	cond = va_arg(ap, int);
+	va_end(ap);
+
+	RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),
+			 "RCU-list traversed in non-reader section!");
+}
 /*
  * Insert a new entry between two known consecutive entries.
  *
@@ -338,6 +357,9 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
 						  member) : NULL; \
 })
 
+#define SIXTH_ARG(a1, a2, a3, a4, a5, a6, ...) a6
+#define COUNT_VARGS(...) SIXTH_ARG(dummy, ## __VA_ARGS__, 4, 3, 2, 1, 0)
+
 /**
  * list_for_each_entry_rcu	-	iterate over rcu list of given type
  * @pos:	the type * to use as a loop cursor.
@@ -348,9 +370,14 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * the _rcu list-mutation primitives such as list_add_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
-#define list_for_each_entry_rcu(pos, head, member) \
-	for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
-		&pos->member != (head); \
+#define list_for_each_entry_rcu(pos, head, member, cond...)		\
+	if (COUNT_VARGS(cond) != 0) {					\
+		__list_check_rcu_cond(0, ## cond);			\
+	} else {							\
+		__list_check_rcu();					\
+	}								\
+	for (pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
+		&pos->member != (head);					\
 		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
 /**
@@ -621,7 +648,12 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
-#define hlist_for_each_entry_rcu(pos, head, member)			\
+#define hlist_for_each_entry_rcu(pos, head, member, cond...)		\
+	if (COUNT_VARGS(cond) != 0) {					\
+		__list_check_rcu_cond(0, ## cond);			\
+	} else {							\
+		__list_check_rcu();					\
+	}								\
 	for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
 			typeof(*(pos)), member);			\
 		pos;							\
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 922bb6848813..712b464ab960 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -223,6 +223,7 @@ int debug_lockdep_rcu_enabled(void);
 int rcu_read_lock_held(void);
 int rcu_read_lock_bh_held(void);
 int rcu_read_lock_sched_held(void);
+int rcu_read_lock_any_held(void);
 
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
@@ -243,6 +244,12 @@ static inline int rcu_read_lock_sched_held(void)
 {
 	return !preemptible();
 }
+
+static inline int rcu_read_lock_any_held(void)
+{
+	return !preemptible();
+}
+
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 #ifdef CONFIG_PROVE_RCU
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index c3bf44ba42e5..9cb30006a5e1 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -298,6 +298,32 @@ int rcu_read_lock_bh_held(void)
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 
+int rcu_read_lock_any_held(void)
+{
+	int lockdep_opinion = 0;
+
+	if (!debug_lockdep_rcu_enabled())
+		return 1;
+	if (!rcu_is_watching())
+		return 0;
+	if (!rcu_lockdep_current_cpu_online())
+		return 0;
+
+	/* Preemptible RCU flavor */
+	if (lock_is_held(&rcu_lock_map))
+		return 1;
+
+	/* BH flavor */
+	if (in_softirq() || irqs_disabled())
+		return 1;
+
+	/* Sched flavor */
+	if (debug_locks)
+		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
+	return lockdep_opinion || !preemptible();
+}
+EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);
+
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 /**
-- 
2.22.0.rc1.311.g5d7573a151-goog