[PATCH v2 3/8] rcusync: Add the CONFIG_PROVE_RCU checks

[Oleg Nesterov <oleg@redhat.com>]

It would be nice to validate that the caller of rcu_sync_is_idle()
holds the corresponding type of RCU read-side lock. Add the new
rcu_sync_ops->held() method and change rcu_sync_is_idle() to
WARN() if it returns false.

This obviously penalizes the readers (fast-path), but only if
CONFIG_PROVE_RCU.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Suggested-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/rcusync.h |    6 ++++++
 kernel/rcu/sync.c       |   20 ++++++++++++++++++++
 2 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/include/linux/rcusync.h b/include/linux/rcusync.h
index ff86315..631a842 100644
--- a/include/linux/rcusync.h
+++ b/include/linux/rcusync.h
@@ -17,9 +17,15 @@ struct rcu_sync_struct {
 	enum rcu_sync_type	gp_type;
 };
 
+extern bool __rcu_sync_is_idle(struct rcu_sync_struct *);
+
 static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss)
 {
+#ifdef CONFIG_PROVE_RCU
+	return __rcu_sync_is_idle(rss);
+#else
 	return !rss->gp_state; /* GP_IDLE */
+#endif
 }
 
 extern void rcu_sync_init(struct rcu_sync_struct *, enum rcu_sync_type);
diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
index 99051b7..0ab7cbd 100644
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -1,21 +1,33 @@
 #include <linux/rcusync.h>
 #include <linux/sched.h>
 
+#ifdef CONFIG_PROVE_RCU
+#define __INIT_HELD(func)	.held = func,
+#else
+#define __INIT_HELD(func)
+#endif
+
 static const struct {
 	void (*sync)(void);
 	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+#ifdef CONFIG_PROVE_RCU
+	int  (*held)(void);
+#endif
 } gp_ops[] = {
 	[RCU_SYNC] = {
 		.sync = synchronize_rcu,
 		.call = call_rcu,
+		__INIT_HELD(rcu_read_lock_held)
 	},
 	[RCU_SCHED_SYNC] = {
 		.sync = synchronize_sched,
 		.call = call_rcu_sched,
+		__INIT_HELD(rcu_read_lock_sched_held)
 	},
 	[RCU_BH_SYNC] = {
 		.sync = synchronize_rcu_bh,
 		.call = call_rcu_bh,
+		__INIT_HELD(rcu_read_lock_bh_held)
 	},
 };
 
@@ -24,6 +36,14 @@ enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
 
 #define	rss_lock	gp_wait.lock
 
+#ifdef CONFIG_PROVE_RCU
+bool __rcu_sync_is_idle(struct rcu_sync_struct *rss)
+{
+	WARN_ON(!gp_ops[rss->gp_type].held());
+	return rss->gp_state == GP_IDLE;
+}
+#endif
+
 void rcu_sync_init(struct rcu_sync_struct *rss, enum rcu_sync_type type)
 {
 	memset(rss, 0, sizeof(*rss));
-- 
1.5.5.1