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Subject[PATCH v2.6.34-rc5 03/12] rcu: leave lockdep enabled after RCU lockdep splat
Date
From: Lai Jiangshan <laijs@cn.fujitsu.com>

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.

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>
---
include/linux/rcupdate.h | 15 +++++++++++----
kernel/lockdep.c | 2 --
2 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 07db2fe..ec9ab49 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -190,6 +190,15 @@ static inline int rcu_read_lock_sched_held(void)

#ifdef CONFIG_PROVE_RCU

+#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
@@ -219,8 +228,7 @@ static inline int rcu_read_lock_sched_held(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); \
})

@@ -237,8 +245,7 @@ static inline int rcu_read_lock_sched_held(void)
*/
#define rcu_dereference_protected(p, c) \
({ \
- if (debug_lockdep_rcu_enabled() && !(c)) \
- lockdep_rcu_dereference(__FILE__, __LINE__); \
+ __do_rcu_dereference_check(c); \
(p); \
})

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 2594e1c..03dd1fa 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3801,8 +3801,6 @@ void lockdep_rcu_dereference(const char *file, const int line)
{
struct task_struct *curr = current;

- if (!debug_locks_off())
- return;
printk("\n===================================================\n");
printk( "[ INFO: suspicious rcu_dereference_check() usage. ]\n");
printk( "---------------------------------------------------\n");
--
1.7.0


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