From db91cf877ba6f42f0bc5d3862373cfc66c722816 Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Mon, 22 Feb 2010 17:04:47 -0800
Subject: [PATCH] --- yaml --- r: 182243 b: refs/heads/master c:
 0632eb3d7563d6a76d49a3860b6352d800c92854 h: refs/heads/master i:   182241:
 dbcb8e274f71a586e2247f524eea7763d4629e4b   182239:
 d7b7cd3976c5236aac4f23dde287e37879bf8a5c v: v3

---
 [refs]                         |  2 +-
 trunk/include/linux/lockdep.h  |  4 ++++
 trunk/include/linux/rcupdate.h |  4 ++--
 trunk/kernel/lockdep.c         | 18 ++++++++++++++++++
 4 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/[refs] b/[refs]
index 8937ca388e01..2baf89cefc54 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: c26d34a5858f96a564c45048bf5f09319d2abad1
+refs/heads/master: 0632eb3d7563d6a76d49a3860b6352d800c92854
diff --git a/trunk/include/linux/lockdep.h b/trunk/include/linux/lockdep.h
index 9ccf0e286b2a..10206a87da19 100644
--- a/trunk/include/linux/lockdep.h
+++ b/trunk/include/linux/lockdep.h
@@ -534,4 +534,8 @@ do {									\
 # define might_lock_read(lock) do { } while (0)
 #endif
 
+#ifdef CONFIG_PROVE_RCU
+extern void lockdep_rcu_dereference(const char *file, const int line);
+#endif
+
 #endif /* __LINUX_LOCKDEP_H */
diff --git a/trunk/include/linux/rcupdate.h b/trunk/include/linux/rcupdate.h
index 839d296a7ac0..1a4de31bd7b4 100644
--- a/trunk/include/linux/rcupdate.h
+++ b/trunk/include/linux/rcupdate.h
@@ -182,8 +182,8 @@ static inline int rcu_read_lock_sched_held(void)
  */
 #define rcu_dereference_check(p, c) \
 	({ \
-		if (debug_locks) \
-			WARN_ON_ONCE(!(c)); \
+		if (debug_locks && !(c)) \
+			lockdep_rcu_dereference(__FILE__, __LINE__); \
 		rcu_dereference_raw(p); \
 	})
 
diff --git a/trunk/kernel/lockdep.c b/trunk/kernel/lockdep.c
index c62ec14609b9..672c436946ce 100644
--- a/trunk/kernel/lockdep.c
+++ b/trunk/kernel/lockdep.c
@@ -3809,3 +3809,21 @@ void lockdep_sys_exit(void)
 		lockdep_print_held_locks(curr);
 	}
 }
+
+void lockdep_rcu_dereference(const char *file, const int line)
+{
+	struct task_struct *curr = current;
+
+	if (!debug_locks_off())
+		return;
+	printk("\n==============================================\n");
+	printk(  "[ BUG: Unsafe rcu_dereference_check() usage! ]\n");
+	printk(  "----------------------------------------------\n");
+	printk("%s:%d invoked rcu_dereference_check() without protection!\n",
+			file, line);
+	printk("\nother info that might help us debug this:\n\n");
+	lockdep_print_held_locks(curr);
+	printk("\nstack backtrace:\n");
+	dump_stack();
+}
+EXPORT_SYMBOL_GPL(lockdep_rcu_dereference);