/* * Read-Copy Update mechanism for mutual exclusion * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * Copyright IBM Corporation, 2001 * * Authors: Dipankar Sarma <dipankar@in.ibm.com> *	    Manfred Spraul <manfred@colorfullife.com> * * Based on the original work by Paul McKenney <paulmck@us.ibm.com> * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. * Papers: * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) * * For detailed explanation of Read-Copy Update mechanism see - *		http://lse.sourceforge.net/locking/rcupdate.html * */#include <linux/types.h>#include <linux/kernel.h>#include <linux/init.h>#include <linux/spinlock.h>#include <linux/smp.h>#include <linux/interrupt.h>#include <linux/sched.h>#include <linux/atomic.h>#include <linux/bitops.h>#include <linux/percpu.h>#include <linux/notifier.h>#include <linux/cpu.h>#include <linux/mutex.h>#include <linux/export.h>#include <linux/hardirq.h>#include <linux/delay.h>#include <linux/module.h> #define CREATE_TRACE_POINTS#include <trace/events/rcu.h> #include "rcu.h" module_param(rcu_expedited, int, 0); #ifdef CONFIG_PREEMPT_RCU /* * Preemptible RCU implementation for rcu_read_lock(). * Just increment ->rcu_read_lock_nesting, shared state will be updated * if we block. */void __rcu_read_lock(void){	current->rcu_read_lock_nesting++;	barrier();  /* critical section after entry code. */}EXPORT_SYMBOL_GPL(__rcu_read_lock); /* * Preemptible RCU implementation for rcu_read_unlock(). * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then * invoke rcu_read_unlock_special() to clean up after a context switch * in an RCU read-side critical section and other special cases. */void __rcu_read_unlock(void){	struct task_struct *t = current; 	if (t->rcu_read_lock_nesting != 1) {		--t->rcu_read_lock_nesting;	} else {		barrier();  /* critical section before exit code. */		t->rcu_read_lock_nesting = INT_MIN;#ifdef CONFIG_PROVE_RCU_DELAY		udelay(10); /* Make preemption more probable. */#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */		barrier();  /* assign before ->rcu_read_unlock_special load */		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))			rcu_read_unlock_special(t);		barrier();  /* ->rcu_read_unlock_special load before assign */		t->rcu_read_lock_nesting = 0;	}#ifdef CONFIG_PROVE_LOCKING	{		int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); 		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);	}#endif /* #ifdef CONFIG_PROVE_LOCKING */}EXPORT_SYMBOL_GPL(__rcu_read_unlock); /* * Check for a task exiting while in a preemptible-RCU read-side * critical section, clean up if so.  No need to issue warnings, * as debug_check_no_locks_held() already does this if lockdep * is enabled. */void exit_rcu(void){	struct task_struct *t = current; 	if (likely(list_empty(&current->rcu_node_entry)))		return;	t->rcu_read_lock_nesting = 1;	barrier();	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;	__rcu_read_unlock();} #else /* #ifdef CONFIG_PREEMPT_RCU */ void exit_rcu(void){} #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ #ifdef CONFIG_DEBUG_LOCK_ALLOCstatic struct lock_class_key rcu_lock_key;struct lockdep_map rcu_lock_map =	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);EXPORT_SYMBOL_GPL(rcu_lock_map); static struct lock_class_key rcu_bh_lock_key;struct lockdep_map rcu_bh_lock_map =	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);EXPORT_SYMBOL_GPL(rcu_bh_lock_map); static struct lock_class_key rcu_sched_lock_key;struct lockdep_map rcu_sched_lock_map =	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);EXPORT_SYMBOL_GPL(rcu_sched_lock_map);#endif #ifdef CONFIG_DEBUG_LOCK_ALLOC int debug_lockdep_rcu_enabled(void){	return rcu_scheduler_active && debug_locks &&	       current->lockdep_recursion == 0;}EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); /** * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? * * Check for bottom half being disabled, which covers both the * CONFIG_PROVE_RCU and not cases.  Note that if someone uses * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) * will show the situation.  This is useful for debug checks in functions * that require that they be called within an RCU read-side critical * section. * * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. * * Note that rcu_read_lock() is disallowed if the CPU is either idle or * offline from an RCU perspective, so check for those as well. */int rcu_read_lock_bh_held(void){	if (!debug_lockdep_rcu_enabled())		return 1;	if (rcu_is_cpu_idle())		return 0;	if (!rcu_lockdep_current_cpu_online())		return 0;	return in_softirq() || irqs_disabled();}EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ struct rcu_synchronize {	struct rcu_head head;	struct completion completion;}; /* * Awaken the corresponding synchronize_rcu() instance now that a * grace period has elapsed. */static void wakeme_after_rcu(struct rcu_head  *head){	struct rcu_synchronize *rcu; 	rcu = container_of(head, struct rcu_synchronize, head);	complete(&rcu->completion);} void wait_rcu_gp(call_rcu_func_t crf){	struct rcu_synchronize rcu; 	init_rcu_head_on_stack(&rcu.head);	init_completion(&rcu.completion);	/* Will wake me after RCU finished. */	crf(&rcu.head, wakeme_after_rcu);	/* Wait for it. */	wait_for_completion(&rcu.completion);	destroy_rcu_head_on_stack(&rcu.head);}EXPORT_SYMBOL_GPL(wait_rcu_gp); #ifdef CONFIG_PROVE_RCU/* * wrapper function to avoid #include problems. */int rcu_my_thread_group_empty(void){	return thread_group_empty(current);}EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);#endif /* #ifdef CONFIG_PROVE_RCU */ #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEADstatic inline void debug_init_rcu_head(struct rcu_head *head){	debug_object_init(head, &rcuhead_debug_descr);} static inline void debug_rcu_head_free(struct rcu_head *head){	debug_object_free(head, &rcuhead_debug_descr);} /* * fixup_init is called when: * - an active object is initialized */static int rcuhead_fixup_init(void *addr, enum debug_obj_state state){	struct rcu_head *head = addr; 	switch (state) {	case ODEBUG_STATE_ACTIVE:		/*		 * Ensure that queued callbacks are all executed.		 * If we detect that we are nested in a RCU read-side critical		 * section, we should simply fail, otherwise we would deadlock.		 * In !PREEMPT configurations, there is no way to tell if we are		 * in a RCU read-side critical section or not, so we never		 * attempt any fixup and just print a warning.		 */#ifndef CONFIG_PREEMPT		WARN_ON_ONCE(1);		return 0;#endif		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||		    irqs_disabled()) {			WARN_ON_ONCE(1);			return 0;		}		rcu_barrier();		rcu_barrier_sched();		rcu_barrier_bh();		debug_object_init(head, &rcuhead_debug_descr);		return 1;	default:		return 0;	}} /* * fixup_activate is called when: * - an active object is activated * - an unknown object is activated (might be a statically initialized object) * Activation is performed internally by call_rcu(). */static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state){	struct rcu_head *head = addr; 	switch (state) { 	case ODEBUG_STATE_NOTAVAILABLE:		/*		 * This is not really a fixup. We just make sure that it is		 * tracked in the object tracker.		 */		debug_object_init(head, &rcuhead_debug_descr);		debug_object_activate(head, &rcuhead_debug_descr);		return 0; 	case ODEBUG_STATE_ACTIVE:		/*		 * Ensure that queued callbacks are all executed.		 * If we detect that we are nested in a RCU read-side critical		 * section, we should simply fail, otherwise we would deadlock.		 * In !PREEMPT configurations, there is no way to tell if we are		 * in a RCU read-side critical section or not, so we never		 * attempt any fixup and just print a warning.		 */#ifndef CONFIG_PREEMPT		WARN_ON_ONCE(1);		return 0;#endif		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||		    irqs_disabled()) {			WARN_ON_ONCE(1);			return 0;		}		rcu_barrier();		rcu_barrier_sched();		rcu_barrier_bh();		debug_object_activate(head, &rcuhead_debug_descr);		return 1;	default:		return 0;	}} /* * fixup_free is called when: * - an active object is freed */static int rcuhead_fixup_free(void *addr, enum debug_obj_state state){	struct rcu_head *head = addr; 	switch (state) {	case ODEBUG_STATE_ACTIVE:		/*		 * Ensure that queued callbacks are all executed.		 * If we detect that we are nested in a RCU read-side critical		 * section, we should simply fail, otherwise we would deadlock.		 * In !PREEMPT configurations, there is no way to tell if we are		 * in a RCU read-side critical section or not, so we never		 * attempt any fixup and just print a warning.		 */#ifndef CONFIG_PREEMPT		WARN_ON_ONCE(1);		return 0;#endif		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||		    irqs_disabled()) {			WARN_ON_ONCE(1);			return 0;		}		rcu_barrier();		rcu_barrier_sched();		rcu_barrier_bh();		debug_object_free(head, &rcuhead_debug_descr);		return 1;	default:		return 0;	}} /** * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects * @head: pointer to rcu_head structure to be initialized * * This function informs debugobjects of a new rcu_head structure that * has been allocated as an auto variable on the stack.  This function * is not required for rcu_head structures that are statically defined or * that are dynamically allocated on the heap.  This function has no * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. */void init_rcu_head_on_stack(struct rcu_head *head){	debug_object_init_on_stack(head, &rcuhead_debug_descr);}EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); /** * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects * @head: pointer to rcu_head structure to be initialized * * This function informs debugobjects that an on-stack rcu_head structure * is about to go out of scope.  As with init_rcu_head_on_stack(), this * function is not required for rcu_head structures that are statically * defined or that are dynamically allocated on the heap.  Also as with * init_rcu_head_on_stack(), this function has no effect for * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. */void destroy_rcu_head_on_stack(struct rcu_head *head){	debug_object_free(head, &rcuhead_debug_descr);}EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); struct debug_obj_descr rcuhead_debug_descr = {	.name = "rcu_head",	.fixup_init = rcuhead_fixup_init,	.fixup_activate = rcuhead_fixup_activate,	.fixup_free = rcuhead_fixup_free,};EXPORT_SYMBOL_GPL(rcuhead_debug_descr);#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp,			       unsigned long secs,			       unsigned long c_old, unsigned long c){	trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);}EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);#else#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \	do { } while (0)#endif #ifdef CONFIG_RCU_STALL_COMMON #ifdef CONFIG_PROVE_RCU#define RCU_STALL_DELAY_DELTA	       (5 * HZ)#else#define RCU_STALL_DELAY_DELTA	       0#endif int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; module_param(rcu_cpu_stall_suppress, int, 0644);module_param(rcu_cpu_stall_timeout, int, 0644); int rcu_jiffies_till_stall_check(void){	int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); 	/*	 * Limit check must be consistent with the Kconfig limits	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.	 */	if (till_stall_check < 3) {		ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;		till_stall_check = 3;	} else if (till_stall_check > 300) {		ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;		till_stall_check = 300;	}	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;} static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr){	rcu_cpu_stall_suppress = 1;	return NOTIFY_DONE;} static struct notifier_block rcu_panic_block = {	.notifier_call = rcu_panic,}; static int __init check_cpu_stall_init(void){	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);	return 0;}early_initcall(check_cpu_stall_init); #endif /* #ifdef CONFIG_RCU_STALL_COMMON */