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Subject[PATCH tip/core/rcu 03/13] rcu: integrate rcu_dereference_check() message into lockdep
Date
Make rcu_dereference_check() print the list of held locks in addition
to the stack dump to ease debugging.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/lockdep.h | 4 ++++
include/linux/rcupdate.h | 4 ++--
kernel/lockdep.c | 18 ++++++++++++++++++
3 files changed, 24 insertions(+), 2 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 9ccf0e2..10206a8 100644
--- a/include/linux/lockdep.h
+++ b/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/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 839d296..1a4de31 100644
--- a/include/linux/rcupdate.h
+++ b/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/kernel/lockdep.c b/kernel/lockdep.c
index 5feaddc..a44c1b2 100644
--- a/kernel/lockdep.c
+++ b/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);
--
1.6.6


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