Prev: [PATCH tip/core/urgent 10/10] vfs: fix RCU-lockdep false positive due to /proc access
Next: [PATCH tip/core/urgent 0/10] v2: Fix RCU lockdep splats
From: Paul E. McKenney on 30 Apr 2010 20:30
From: Lai Jiangshan <laijs(a)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.

This is controlled by a new config variable CONFIG_PROVE_RCU_REPEATEDLY,
which is disabled by default.

Requested-by: Eric Paris <eparis(a)redhat.com>
Signed-off-by: Lai Jiangshan <laijs(a)cn.fujitsu.com>
Tested-by: Eric Paris <eparis(a)redhat.com>
Signed-off-by: Paul E. McKenney <paulmck(a)linux.vnet.ibm.com>
---
include/linux/rcupdate.h | 15 +++++++++++----
kernel/lockdep.c | 2 ++
lib/Kconfig.debug | 12 ++++++++++++
3 files changed, 25 insertions(+), 4 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..73747b7 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3801,8 +3801,10 @@ void lockdep_rcu_dereference(const char *file, const int line)
{
struct task_struct *curr = current;

+#ifndef CONFIG_PROVE_RCU_REPEATEDLY
if (!debug_locks_off())
return;
+#endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
printk("\n===================================================\n");
printk( "[ INFO: suspicious rcu_dereference_check() usage. ]\n");
printk( "---------------------------------------------------\n");
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 935248b..94090b4 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -512,6 +512,18 @@ config PROVE_RCU

Say N if you are unsure.

+config PROVE_RCU_REPEATEDLY
+ bool "RCU debugging: don't disable PROVE_RCU on first splat"
+ depends on PROVE_RCU
+ default n
+ help
+ By itself, PROVE_RCU will disable checking upon issuing the
+ first warning (or "splat"). This feature prevents such
+ disabling, allowing multiple RCU-lockdep warnings to be printed
+ on a single reboot.
+
+ Say N if you are unsure.
+
config LOCKDEP
bool
depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
--
1.7.0

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
 | 
Pages: 1
Prev: [PATCH tip/core/urgent 10/10] vfs: fix RCU-lockdep false positive due to /proc access
Next: [PATCH tip/core/urgent 0/10] v2: Fix RCU lockdep splats