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>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index db266bb..4dca275 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -192,6 +192,15 @@
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 @@
*/
#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 @@
*/
#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..3a756ba 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3801,8 +3801,11 @@
{
struct task_struct *curr = current;
+#ifndef CONFIG_PROVE_RCU_REPEATEDLY
if (!debug_locks_off())
return;
+#endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
+ /* Note: the following can be executed concurrently, so be careful. */
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 @@
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