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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>
This commit is contained in:
Lai Jiangshan 2010-04-20 16:23:07 +08:00 committed by Paul E. McKenney
parent b57f95a382
commit 2b3fc35f69
3 changed files with 26 additions and 4 deletions
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15
include/linux/rcupdate.h
View File

@ -192,6 +192,15 @@ static inline int rcu_read_lock_sched_held(void)
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 @@ extern int rcu_my_thread_group_empty(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); \
})
@ -239,8 +247,7 @@ extern int rcu_my_thread_group_empty(void);
*/
#define rcu_dereference_protected(p, c) \
({ \
if (debug_lockdep_rcu_enabled() && !(c)) \
lockdep_rcu_dereference(__FILE__, __LINE__); \
__do_rcu_dereference_check(c); \
(p); \
})

3
kernel/lockdep.c
View File

@ -3801,8 +3801,11 @@ 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 */
/* Note: the following can be executed concurrently, so be careful. */
printk("\n===================================================\n");
printk( "[ INFO: suspicious rcu_dereference_check() usage. ]\n");
printk( "---------------------------------------------------\n");

12
lib/Kconfig.debug
View File

@ -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