rcu: optionally leave lockdep enabled after RCU lockdep splat

There is no need to disable lockdep after an RCU lockdep splat,
so remove the debug_lockdeps_off() from lockdep_rcu_dereference().
To avoid repeated lockdep splats, use a static variable in the inlined
rcu_dereference_check() and rcu_dereference_protected() macros so that
a given instance splats only once, but so that multiple instances can
be detected per boot.

This is controlled by a new config variable CONFIG_PROVE_RCU_REPEATEDLY,
which is disabled by default.  This provides the normal lockdep behavior
by default, but permits people who want to find multiple RCU-lockdep
splats per boot to easily do so.

Requested-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Tested-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index db266bbed23f..4dca2752cfde 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -192,6 +192,15 @@ static inline int rcu_read_lock_sched_held(void)
 
 extern int rcu_my_thread_group_empty(void);
 
+#define __do_rcu_dereference_check(c)                                   \
+        do {                                                            \
+                static bool __warned;                                   \
+                if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
+                        __warned = true;                                \
+                        lockdep_rcu_dereference(__FILE__, __LINE__);    \
+                }                                                       \
+        } while (0)
+
 /**
  * rcu_dereference_check - rcu_dereference with debug checking
  * @p: The pointer to read, prior to dereferencing
@@ -221,8 +230,7 @@ extern int rcu_my_thread_group_empty(void);
  */
 #define rcu_dereference_check(p, c) \
         ({ \
-                if (debug_lockdep_rcu_enabled() && !(c)) \
-                        lockdep_rcu_dereference(__FILE__, __LINE__); \
+                __do_rcu_dereference_check(c); \
                 rcu_dereference_raw(p); \
         })
 
@@ -239,8 +247,7 @@ extern int rcu_my_thread_group_empty(void);
  */
 #define rcu_dereference_protected(p, c) \
         ({ \
-                if (debug_lockdep_rcu_enabled() && !(c)) \
-                        lockdep_rcu_dereference(__FILE__, __LINE__); \
+                __do_rcu_dereference_check(c); \
                 (p); \
         })