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Commit 2b3fc35f authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Paul E. McKenney
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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: default avatarEric Paris <eparis@redhat.com>
Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Tested-by: default avatarEric Paris <eparis@redhat.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent b57f95a3

include/linux/rcupdate.h

+11 −4
Original line number Diff line number Diff line
@@ -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); \

	})

kernel/lockdep.c

+3 −0
Original line number Diff line number Diff line
@@ -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");

lib/Kconfig.debug

+12 −0
Original line number Diff line number Diff line
@@ -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