Commit d9f1bb6a authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
Browse files

rcu: Make rcu_read_lock_sched_held() take boot time into account 



Before the scheduler starts, all tasks are non-preemptible by
definition. So, during that time, rcu_read_lock_sched_held()
needs to always return "true".  This patch makes that be so.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1267135607-7056-2-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 056ba4a9

include/linux/rcupdate.h

+3 −1
Original line number Diff line number Diff line
@@ -62,6 +62,8 @@ extern int sched_expedited_torture_stats(char *page); 


/* Internal to kernel */

extern void rcu_init(void);

extern int rcu_scheduler_active;

extern void rcu_scheduler_starting(void);



#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)

#include <linux/rcutree.h>
@@ -140,7 +142,7 @@ static inline int rcu_read_lock_sched_held(void) 


	if (debug_locks)

		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);

	return lockdep_opinion || preempt_count() != 0;

	return lockdep_opinion || preempt_count() != 0 || !rcu_scheduler_active;

}



#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

include/linux/rcutiny.h

+0 −4
Original line number Diff line number Diff line
@@ -105,10 +105,6 @@ static inline void rcu_exit_nohz(void) 


#endif /* #else #ifdef CONFIG_NO_HZ */



static inline void rcu_scheduler_starting(void)

{

}



static inline void exit_rcu(void)

{

}

include/linux/rcutree.h

+0 −1
Original line number Diff line number Diff line
@@ -35,7 +35,6 @@ struct notifier_block; 
extern void rcu_sched_qs(int cpu);

extern void rcu_bh_qs(int cpu);

extern int rcu_needs_cpu(int cpu);

extern void rcu_scheduler_starting(void);

extern int rcu_expedited_torture_stats(char *page);



#ifdef CONFIG_TREE_PREEMPT_RCU

kernel/rcupdate.c

+18 −0
Original line number Diff line number Diff line
@@ -44,6 +44,7 @@ 
#include <linux/cpu.h>

#include <linux/mutex.h>

#include <linux/module.h>

#include <linux/kernel_stat.h>



#ifdef CONFIG_DEBUG_LOCK_ALLOC

static struct lock_class_key rcu_lock_key;
@@ -62,6 +63,23 @@ struct lockdep_map rcu_sched_lock_map = 
EXPORT_SYMBOL_GPL(rcu_sched_lock_map);

#endif



int rcu_scheduler_active __read_mostly;



/*

 * This function is invoked towards the end of the scheduler's initialization

 * process.  Before this is called, the idle task might contain

 * RCU read-side critical sections (during which time, this idle

 * task is booting the system).  After this function is called, the

 * idle tasks are prohibited from containing RCU read-side critical

 * sections.

 */

void rcu_scheduler_starting(void)

{

	WARN_ON(num_online_cpus() != 1);

	WARN_ON(nr_context_switches() > 0);

	rcu_scheduler_active = 1;

}



/*

 * Awaken the corresponding synchronize_rcu() instance now that a

 * grace period has elapsed.

kernel/rcutree.c

+0 −19
Original line number Diff line number Diff line
@@ -46,7 +46,6 @@ 
#include <linux/cpu.h>

#include <linux/mutex.h>

#include <linux/time.h>

#include <linux/kernel_stat.h>



#include "rcutree.h"
@@ -81,9 +80,6 @@ DEFINE_PER_CPU(struct rcu_data, rcu_sched_data); 
struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);

DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);



static int rcu_scheduler_active __read_mostly;





/*

 * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s

 * permit this function to be invoked without holding the root rcu_node
@@ -1565,21 +1561,6 @@ static int rcu_needs_cpu_quick_check(int cpu) 
	       rcu_preempt_needs_cpu(cpu);

}



/*

 * This function is invoked towards the end of the scheduler's initialization

 * process.  Before this is called, the idle task might contain

 * RCU read-side critical sections (during which time, this idle

 * task is booting the system).  After this function is called, the

 * idle tasks are prohibited from containing RCU read-side critical

 * sections.

 */

void rcu_scheduler_starting(void)

{

	WARN_ON(num_online_cpus() != 1);

	WARN_ON(nr_context_switches() > 0);

	rcu_scheduler_active = 1;

}



static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};

static atomic_t rcu_barrier_cpu_count;

static DEFINE_MUTEX(rcu_barrier_mutex);

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