Commit 28875945 authored by Joel Fernandes (Google)'s avatar Joel Fernandes (Google) Committed by Paul E. McKenney
Browse files

rcu: Add support for consolidated-RCU reader checking 



This commit adds RCU-reader checks to list_for_each_entry_rcu() and
hlist_for_each_entry_rcu().  These checks are optional, and are indicated
by a lockdep expression passed to a new optional argument to these two
macros.  If this optional lockdep expression is omitted, these two macros
act as before, checking for an RCU read-side critical section.

Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Update to eliminate return within macro and update comment. ]
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 9147089b

include/linux/rculist.h

+27 −5
Original line number Diff line number Diff line
@@ -40,6 +40,24 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list) 
 */

#define list_next_rcu(list)	(*((struct list_head __rcu **)(&(list)->next)))



/*

 * Check during list traversal that we are within an RCU reader

 */



#define check_arg_count_one(dummy)



#ifdef CONFIG_PROVE_RCU_LIST

#define __list_check_rcu(dummy, cond, extra...)				\

	({								\

	check_arg_count_one(extra);					\

	RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),		\

			 "RCU-list traversed in non-reader section!");	\

	 })

#else

#define __list_check_rcu(dummy, cond, extra...)				\

	({ check_arg_count_one(extra); })

#endif



/*

 * Insert a new entry between two known consecutive entries.

 *
@@ -343,13 +361,15 @@ static inline void list_splice_tail_init_rcu(struct list_head *list, 
 * @pos:	the type * to use as a loop cursor.

 * @head:	the head for your list.

 * @member:	the name of the list_head within the struct.

 * @cond:	optional lockdep expression if called from non-RCU protection.

 *

 * This list-traversal primitive may safely run concurrently with

 * the _rcu list-mutation primitives such as list_add_rcu()

 * as long as the traversal is guarded by rcu_read_lock().

 */

#define list_for_each_entry_rcu(pos, head, member) \

	for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \

#define list_for_each_entry_rcu(pos, head, member, cond...)		\

	for (__list_check_rcu(dummy, ## cond, 0),			\

	     pos = list_entry_rcu((head)->next, typeof(*pos), member);	\

		&pos->member != (head);					\

		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
@@ -616,13 +636,15 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n, 
 * @pos:	the type * to use as a loop cursor.

 * @head:	the head for your list.

 * @member:	the name of the hlist_node within the struct.

 * @cond:	optional lockdep expression if called from non-RCU protection.

 *

 * This list-traversal primitive may safely run concurrently with

 * the _rcu list-mutation primitives such as hlist_add_head_rcu()

 * as long as the traversal is guarded by rcu_read_lock().

 */

#define hlist_for_each_entry_rcu(pos, head, member)			\

	for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\

#define hlist_for_each_entry_rcu(pos, head, member, cond...)		\

	for (__list_check_rcu(dummy, ## cond, 0),			\

	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\

			typeof(*(pos)), member);			\

		pos;							\

		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\

include/linux/rcupdate.h

+7 −0
Original line number Diff line number Diff line
@@ -221,6 +221,7 @@ int debug_lockdep_rcu_enabled(void); 
int rcu_read_lock_held(void);

int rcu_read_lock_bh_held(void);

int rcu_read_lock_sched_held(void);

int rcu_read_lock_any_held(void);



#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -241,6 +242,12 @@ static inline int rcu_read_lock_sched_held(void) 
{

	return !preemptible();

}



static inline int rcu_read_lock_any_held(void)

{

	return !preemptible();

}



#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */



#ifdef CONFIG_PROVE_RCU

kernel/rcu/Kconfig.debug

+11 −0
Original line number Diff line number Diff line
@@ -8,6 +8,17 @@ menu "RCU Debugging" 
config PROVE_RCU

	def_bool PROVE_LOCKING



config PROVE_RCU_LIST

	bool "RCU list lockdep debugging"

	depends on PROVE_RCU && RCU_EXPERT

	default n

	help

	  Enable RCU lockdep checking for list usages. By default it is

	  turned off since there are several list RCU users that still

	  need to be converted to pass a lockdep expression. To prevent

	  false-positive splats, we keep it default disabled but once all

	  users are converted, we can remove this config option.



config TORTURE_TEST

	tristate

	default n

kernel/rcu/update.c

+63 −33
Original line number Diff line number Diff line
@@ -61,9 +61,15 @@ module_param(rcu_normal_after_boot, int, 0); 


#ifdef CONFIG_DEBUG_LOCK_ALLOC

/**

 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?

 * rcu_read_lock_held_common() - might we be in RCU-sched read-side critical section?

 * @ret:	Best guess answer if lockdep cannot be relied on

 *

 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an

 * Returns true if lockdep must be ignored, in which case *ret contains

 * the best guess described below.  Otherwise returns false, in which

 * case *ret tells the caller nothing and the caller should instead

 * consult lockdep.

 *

 * If CONFIG_DEBUG_LOCK_ALLOC is selected, set *ret to nonzero iff in an

 * RCU-sched read-side critical section.  In absence of

 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side

 * critical section unless it can prove otherwise.  Note that disabling
@@ -75,30 +81,44 @@ module_param(rcu_normal_after_boot, int, 0); 
 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot

 * and while lockdep is disabled.

 *

 * Note that if the CPU is in the idle loop from an RCU point of

 * view (ie: that we are in the section between rcu_idle_enter() and

 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU

 * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs

 * that are in such a section, considering these as in extended quiescent

 * state, so such a CPU is effectively never in an RCU read-side critical

 * section regardless of what RCU primitives it invokes.  This state of

 * affairs is required --- we need to keep an RCU-free window in idle

 * where the CPU may possibly enter into low power mode. This way we can

 * notice an extended quiescent state to other CPUs that started a grace

 * period. Otherwise we would delay any grace period as long as we run in

 * the idle task.

 *

 * Similarly, we avoid claiming an SRCU read lock held if the current

 * Note that if the CPU is in the idle loop from an RCU point of view (ie:

 * that we are in the section between rcu_idle_enter() and rcu_idle_exit())

 * then rcu_read_lock_held() sets *ret to false even if the CPU did an

 * rcu_read_lock().  The reason for this is that RCU ignores CPUs that are

 * in such a section, considering these as in extended quiescent state,

 * so such a CPU is effectively never in an RCU read-side critical section

 * regardless of what RCU primitives it invokes.  This state of affairs is

 * required --- we need to keep an RCU-free window in idle where the CPU may

 * possibly enter into low power mode. This way we can notice an extended

 * quiescent state to other CPUs that started a grace period. Otherwise

 * we would delay any grace period as long as we run in the idle task.

 *

 * Similarly, we avoid claiming an RCU read lock held if the current

 * CPU is offline.

 */

static bool rcu_read_lock_held_common(bool *ret)

{

	if (!debug_lockdep_rcu_enabled()) {

		*ret = 1;

		return true;

	}

	if (!rcu_is_watching()) {

		*ret = 0;

		return true;

	}

	if (!rcu_lockdep_current_cpu_online()) {

		*ret = 0;

		return true;

	}

	return false;

}



int rcu_read_lock_sched_held(void)

{

	if (!debug_lockdep_rcu_enabled())

		return 1;

	if (!rcu_is_watching())

		return 0;

	if (!rcu_lockdep_current_cpu_online())

		return 0;

	bool ret;



	if (rcu_read_lock_held_common(&ret))

		return ret;

	return lock_is_held(&rcu_sched_lock_map) || !preemptible();

}

EXPORT_SYMBOL(rcu_read_lock_sched_held);
@@ -257,12 +277,10 @@ NOKPROBE_SYMBOL(debug_lockdep_rcu_enabled); 
 */

int rcu_read_lock_held(void)

{

	if (!debug_lockdep_rcu_enabled())

		return 1;

	if (!rcu_is_watching())

		return 0;

	if (!rcu_lockdep_current_cpu_online())

		return 0;

	bool ret;



	if (rcu_read_lock_held_common(&ret))

		return ret;

	return lock_is_held(&rcu_lock_map);

}

EXPORT_SYMBOL_GPL(rcu_read_lock_held);
@@ -284,16 +302,28 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_held); 
 */

int rcu_read_lock_bh_held(void)

{

	if (!debug_lockdep_rcu_enabled())

		return 1;

	if (!rcu_is_watching())

		return 0;

	if (!rcu_lockdep_current_cpu_online())

		return 0;

	bool ret;



	if (rcu_read_lock_held_common(&ret))

		return ret;

	return in_softirq() || irqs_disabled();

}

EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);



int rcu_read_lock_any_held(void)

{

	bool ret;



	if (rcu_read_lock_held_common(&ret))

		return ret;

	if (lock_is_held(&rcu_lock_map) ||

	    lock_is_held(&rcu_bh_lock_map) ||

	    lock_is_held(&rcu_sched_lock_map))

		return 1;

	return !preemptible();

}

EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);



#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */



/**

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