/* * 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, you can access it online at * http://www.gnu.org/licenses/gpl-2.0.html. * * 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>#include <linux/kthread.h>#include <linux/tick.h> #define CREATE_TRACE_POINTS #include "rcu.h" MODULE_ALIAS("rcupdate");#ifdef MODULE_PARAM_PREFIX#undef MODULE_PARAM_PREFIX#endif#define MODULE_PARAM_PREFIX "rcupdate." module_param(rcu_expedited, int, 0); #ifndef CONFIG_TINY_RCU static atomic_t rcu_expedited_nesting =	ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0); /* * Should normal grace-period primitives be expedited?  Intended for * use within RCU.  Note that this function takes the rcu_expedited * sysfs/boot variable into account as well as the rcu_expedite_gp() * nesting.  So looping on rcu_unexpedite_gp() until rcu_gp_is_expedited() * returns false is a -really- bad idea. */bool rcu_gp_is_expedited(void){	return rcu_expedited || atomic_read(&rcu_expedited_nesting);}EXPORT_SYMBOL_GPL(rcu_gp_is_expedited); /** * rcu_expedite_gp - Expedite future RCU grace periods * * After a call to this function, future calls to synchronize_rcu() and * friends act as the corresponding synchronize_rcu_expedited() function * had instead been called. */void rcu_expedite_gp(void){	atomic_inc(&rcu_expedited_nesting);}EXPORT_SYMBOL_GPL(rcu_expedite_gp); /** * rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation * * Undo a prior call to rcu_expedite_gp().  If all prior calls to * rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(), * and if the rcu_expedited sysfs/boot parameter is not set, then all * subsequent calls to synchronize_rcu() and friends will return to * their normal non-expedited behavior. */void rcu_unexpedite_gp(void){	atomic_dec(&rcu_expedited_nesting);}EXPORT_SYMBOL_GPL(rcu_unexpedite_gp); #endif /* #ifndef CONFIG_TINY_RCU */ /* * Inform RCU of the end of the in-kernel boot sequence. */void rcu_end_inkernel_boot(void){	if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT))		rcu_unexpedite_gp();} #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;		barrier();  /* assign before ->rcu_read_unlock_special load */		if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))			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 = READ_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); #endif /* #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); static struct lock_class_key rcu_callback_key;struct lockdep_map rcu_callback_map =	STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);EXPORT_SYMBOL_GPL(rcu_callback_map); int notrace 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_held() - might we be in RCU read-side critical section? * * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC, * this assumes we are in an RCU read-side critical section unless it can * prove otherwise.  This is useful for debug checks in functions that * require that they be called within an RCU read-side critical section. * * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot * and while lockdep is disabled. * * Note that rcu_read_lock() and the matching rcu_read_unlock() must * occur in the same context, for example, it is illegal to invoke * rcu_read_unlock() in process context if the matching rcu_read_lock() * was invoked from within an irq handler. * * 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_held(void){	if (!debug_lockdep_rcu_enabled())		return 1;	if (!rcu_is_watching())		return 0;	if (!rcu_lockdep_current_cpu_online())		return 0;	return lock_is_held(&rcu_lock_map);}EXPORT_SYMBOL_GPL(rcu_read_lock_held); /** * 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_watching())		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 */ /** * wakeme_after_rcu() - Callback function to awaken a task after grace period * @head: Pointer to rcu_head member within rcu_synchronize structure * * Awaken the corresponding task now that a grace period has elapsed. */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_DEBUG_OBJECTS_RCU_HEADvoid init_rcu_head(struct rcu_head *head){	debug_object_init(head, &rcuhead_debug_descr);} void destroy_rcu_head(struct rcu_head *head){	debug_object_free(head, &rcuhead_debug_descr);} /* * 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;	default:		return 1;	}} /** * 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_activate = rcuhead_fixup_activate,};EXPORT_SYMBOL_GPL(rcuhead_debug_descr);#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)void do_trace_rcu_torture_read(const 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. */static 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 = READ_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) {		WRITE_ONCE(rcu_cpu_stall_timeout, 3);		till_stall_check = 3;	} else if (till_stall_check > 300) {		WRITE_ONCE(rcu_cpu_stall_timeout, 300);		till_stall_check = 300;	}	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;} void rcu_sysrq_start(void){	if (!rcu_cpu_stall_suppress)		rcu_cpu_stall_suppress = 2;} void rcu_sysrq_end(void){	if (rcu_cpu_stall_suppress == 2)		rcu_cpu_stall_suppress = 0;} 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 */ #ifdef CONFIG_TASKS_RCU /* * Simple variant of RCU whose quiescent states are voluntary context switch, * user-space execution, and idle.  As such, grace periods can take one good * long time.  There are no read-side primitives similar to rcu_read_lock() * and rcu_read_unlock() because this implementation is intended to get * the system into a safe state for some of the manipulations involved in * tracing and the like.  Finally, this implementation does not support * high call_rcu_tasks() rates from multiple CPUs.  If this is required, * per-CPU callback lists will be needed. */ /* Global list of callbacks and associated lock. */static struct rcu_head *rcu_tasks_cbs_head;static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock); /* Track exiting tasks in order to allow them to be waited for. */DEFINE_SRCU(tasks_rcu_exit_srcu); /* Control stall timeouts.  Disable with <= 0, otherwise jiffies till stall. */static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;module_param(rcu_task_stall_timeout, int, 0644); static void rcu_spawn_tasks_kthread(void); /* * Post an RCU-tasks callback.  First call must be from process context * after the scheduler if fully operational. */void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp)){	unsigned long flags;	bool needwake; 	rhp->next = NULL;	rhp->func = func;	raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);	needwake = !rcu_tasks_cbs_head;	*rcu_tasks_cbs_tail = rhp;	rcu_tasks_cbs_tail = &rhp->next;	raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);	if (needwake) {		rcu_spawn_tasks_kthread();		wake_up(&rcu_tasks_cbs_wq);	}}EXPORT_SYMBOL_GPL(call_rcu_tasks); /** * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. * * Control will return to the caller some time after a full rcu-tasks * grace period has elapsed, in other words after all currently * executing rcu-tasks read-side critical sections have elapsed.  These * read-side critical sections are delimited by calls to schedule(), * cond_resched_rcu_qs(), idle execution, userspace execution, calls * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). * * This is a very specialized primitive, intended only for a few uses in

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