/* * 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 (C) 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/rcupdate.h>#include <linux/interrupt.h>#include <linux/sched.h>#include <asm/atomic.h>#include <linux/bitops.h>#include <linux/module.h>#include <linux/completion.h>#include <linux/moduleparam.h>#include <linux/percpu.h>#include <linux/notifier.h>#include <linux/rcupdate.h>#include <linux/cpu.h>#include <linux/mutex.h> /* Definition for rcupdate control block. */static struct rcu_ctrlblk rcu_ctrlblk = {	.cur = -300,	.completed = -300,	.lock = SPIN_LOCK_UNLOCKED,	.cpumask = CPU_MASK_NONE,};static struct rcu_ctrlblk rcu_bh_ctrlblk = {	.cur = -300,	.completed = -300,	.lock = SPIN_LOCK_UNLOCKED,	.cpumask = CPU_MASK_NONE,}; DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L }; /* Fake initialization required by compiler */static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};static int blimit = 10;static int qhimark = 10000;static int qlowmark = 100;#ifdef CONFIG_SMPstatic int rsinterval = 1000;#endif static atomic_t rcu_barrier_cpu_count;static DEFINE_MUTEX(rcu_barrier_mutex);static struct completion rcu_barrier_completion; #ifdef CONFIG_SMPstatic void force_quiescent_state(struct rcu_data *rdp,			struct rcu_ctrlblk *rcp){	int cpu;	cpumask_t cpumask;	set_need_resched();	if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {		rdp->last_rs_qlen = rdp->qlen;		/*		 * Don't send IPI to itself. With irqs disabled,		 * rdp->cpu is the current cpu.		 */		cpumask = rcp->cpumask;		cpu_clear(rdp->cpu, cpumask);		for_each_cpu_mask(cpu, cpumask)			smp_send_reschedule(cpu);	}}#elsestatic inline void force_quiescent_state(struct rcu_data *rdp,			struct rcu_ctrlblk *rcp){	set_need_resched();}#endif /** * call_rcu - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period * * The update function will be invoked some time after a full grace * period elapses, in other words after all currently executing RCU * read-side critical sections have completed.  RCU read-side critical * sections are delimited by rcu_read_lock() and rcu_read_unlock(), * and may be nested. */void fastcall call_rcu(struct rcu_head *head,				void (*func)(struct rcu_head *rcu)){	unsigned long flags;	struct rcu_data *rdp; 	head->func = func;	head->next = NULL;	local_irq_save(flags);	rdp = &__get_cpu_var(rcu_data);	*rdp->nxttail = head;	rdp->nxttail = &head->next;	if (unlikely(++rdp->qlen > qhimark)) {		rdp->blimit = INT_MAX;		force_quiescent_state(rdp, &rcu_ctrlblk);	}	local_irq_restore(flags);} /** * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period * * The update function will be invoked some time after a full grace * period elapses, in other words after all currently executing RCU * read-side critical sections have completed. call_rcu_bh() assumes * that the read-side critical sections end on completion of a softirq * handler. This means that read-side critical sections in process * context must not be interrupted by softirqs. This interface is to be * used when most of the read-side critical sections are in softirq context. * RCU read-side critical sections are delimited by rcu_read_lock() and * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh() * and rcu_read_unlock_bh(), if in process context. These may be nested. */void fastcall call_rcu_bh(struct rcu_head *head,				void (*func)(struct rcu_head *rcu)){	unsigned long flags;	struct rcu_data *rdp; 	head->func = func;	head->next = NULL;	local_irq_save(flags);	rdp = &__get_cpu_var(rcu_bh_data);	*rdp->nxttail = head;	rdp->nxttail = &head->next; 	if (unlikely(++rdp->qlen > qhimark)) {		rdp->blimit = INT_MAX;		force_quiescent_state(rdp, &rcu_bh_ctrlblk);	} 	local_irq_restore(flags);} /* * Return the number of RCU batches processed thus far.  Useful * for debug and statistics. */long rcu_batches_completed(void){	return rcu_ctrlblk.completed;} static void rcu_barrier_callback(struct rcu_head *notused){	if (atomic_dec_and_test(&rcu_barrier_cpu_count))		complete(&rcu_barrier_completion);} /* * Called with preemption disabled, and from cross-cpu IRQ context. */static void rcu_barrier_func(void *notused){	int cpu = smp_processor_id();	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);	struct rcu_head *head; 	head = &rdp->barrier;	atomic_inc(&rcu_barrier_cpu_count);	call_rcu(head, rcu_barrier_callback);} /** * rcu_barrier - Wait until all the in-flight RCUs are complete. */void rcu_barrier(void){	BUG_ON(in_interrupt());	/* Take cpucontrol mutex to protect against CPU hotplug */	mutex_lock(&rcu_barrier_mutex);	init_completion(&rcu_barrier_completion);	atomic_set(&rcu_barrier_cpu_count, 0);	on_each_cpu(rcu_barrier_func, NULL, 0, 1);	wait_for_completion(&rcu_barrier_completion);	mutex_unlock(&rcu_barrier_mutex);}EXPORT_SYMBOL_GPL(rcu_barrier); /* * Invoke the completed RCU callbacks. They are expected to be in * a per-cpu list. */static void rcu_do_batch(struct rcu_data *rdp){	struct rcu_head *next, *list;	int count = 0; 	list = rdp->donelist;	while (list) {		next = rdp->donelist = list->next;		list->func(list);		list = next;		rdp->qlen--;		if (++count >= rdp->blimit)			break;	}	if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)		rdp->blimit = blimit;	if (!rdp->donelist)		rdp->donetail = &rdp->donelist;	else		tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));} /* * Grace period handling: * The grace period handling consists out of two steps: * - A new grace period is started. *   This is done by rcu_start_batch. The start is not broadcasted to *   all cpus, they must pick this up by comparing rcp->cur with *   rdp->quiescbatch. All cpus are recorded  in the *   rcu_ctrlblk.cpumask bitmap. * - All cpus must go through a quiescent state. *   Since the start of the grace period is not broadcasted, at least two *   calls to rcu_check_quiescent_state are required: *   The first call just notices that a new grace period is running. The *   following calls check if there was a quiescent state since the beginning *   of the grace period. If so, it updates rcu_ctrlblk.cpumask. If *   the bitmap is empty, then the grace period is completed. *   rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace *   period (if necessary). *//* * Register a new batch of callbacks, and start it up if there is currently no * active batch and the batch to be registered has not already occurred. * Caller must hold rcu_ctrlblk.lock. */static void rcu_start_batch(struct rcu_ctrlblk *rcp){	if (rcp->next_pending &&			rcp->completed == rcp->cur) {		rcp->next_pending = 0;		/*		 * next_pending == 0 must be visible in		 * __rcu_process_callbacks() before it can see new value of cur.		 */		smp_wmb();		rcp->cur++; 		/*		 * Accessing nohz_cpu_mask before incrementing rcp->cur needs a		 * Barrier  Otherwise it can cause tickless idle CPUs to be		 * included in rcp->cpumask, which will extend graceperiods		 * unnecessarily.		 */		smp_mb();		cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask); 	}} /* * cpu went through a quiescent state since the beginning of the grace period. * Clear it from the cpu mask and complete the grace period if it was the last * cpu. Start another grace period if someone has further entries pending */static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp){	cpu_clear(cpu, rcp->cpumask);	if (cpus_empty(rcp->cpumask)) {		/* batch completed ! */		rcp->completed = rcp->cur;		rcu_start_batch(rcp);	}} /* * Check if the cpu has gone through a quiescent state (say context * switch). If so and if it already hasn't done so in this RCU * quiescent cycle, then indicate that it has done so. */static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,					struct rcu_data *rdp){	if (rdp->quiescbatch != rcp->cur) {		/* start new grace period: */		rdp->qs_pending = 1;		rdp->passed_quiesc = 0;		rdp->quiescbatch = rcp->cur;		return;	} 	/* Grace period already completed for this cpu?	 * qs_pending is checked instead of the actual bitmap to avoid	 * cacheline trashing.	 */	if (!rdp->qs_pending)		return; 	/* 	 * Was there a quiescent state since the beginning of the grace	 * period? If no, then exit and wait for the next call.	 */	if (!rdp->passed_quiesc)		return;	rdp->qs_pending = 0; 	spin_lock(&rcp->lock);	/*	 * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync	 * during cpu startup. Ignore the quiescent state.	 */	if (likely(rdp->quiescbatch == rcp->cur))		cpu_quiet(rdp->cpu, rcp); 	spin_unlock(&rcp->lock);}  #ifdef CONFIG_HOTPLUG_CPU /* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing * locking requirements, the list it's pulling from has to belong to a cpu * which is dead and hence not processing interrupts. */static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,				struct rcu_head **tail){	local_irq_disable();	*this_rdp->nxttail = list;	if (list)		this_rdp->nxttail = tail;	local_irq_enable();} static void __rcu_offline_cpu(struct rcu_data *this_rdp,				struct rcu_ctrlblk *rcp, struct rcu_data *rdp){	/* if the cpu going offline owns the grace period	 * we can block indefinitely waiting for it, so flush	 * it here	 */	spin_lock_bh(&rcp->lock);	if (rcp->cur != rcp->completed)		cpu_quiet(rdp->cpu, rcp);	spin_unlock_bh(&rcp->lock);	rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);	rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);	rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);} static void rcu_offline_cpu(int cpu){	struct rcu_data *this_rdp = &get_cpu_var(rcu_data);	struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data); 	__rcu_offline_cpu(this_rdp, &rcu_ctrlblk,					&per_cpu(rcu_data, cpu));	__rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,					&per_cpu(rcu_bh_data, cpu));	put_cpu_var(rcu_data);	put_cpu_var(rcu_bh_data);	tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);} #else static void rcu_offline_cpu(int cpu){} #endif /* * This does the RCU processing work from tasklet context.  */static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,					struct rcu_data *rdp){	if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {		*rdp->donetail = rdp->curlist;		rdp->donetail = rdp->curtail;		rdp->curlist = NULL;		rdp->curtail = &rdp->curlist;	} 	if (rdp->nxtlist && !rdp->curlist) {		local_irq_disable();		rdp->curlist = rdp->nxtlist;		rdp->curtail = rdp->nxttail;		rdp->nxtlist = NULL;		rdp->nxttail = &rdp->nxtlist;		local_irq_enable(); 		/*		 * start the next batch of callbacks		 */ 		/* determine batch number */		rdp->batch = rcp->cur + 1;		/* see the comment and corresponding wmb() in		 * the rcu_start_batch()		 */		smp_rmb(); 		if (!rcp->next_pending) {			/* and start it/schedule start if it's a new batch */			spin_lock(&rcp->lock);			rcp->next_pending = 1;			rcu_start_batch(rcp);			spin_unlock(&rcp->lock);		}	} 	rcu_check_quiescent_state(rcp, rdp);	if (rdp->donelist)		rcu_do_batch(rdp);} static void rcu_process_callbacks(unsigned long unused){	__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));	__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));} static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp){	/* This cpu has pending rcu entries and the grace period	 * for them has completed.	 */	if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))		return 1; 	/* This cpu has no pending entries, but there are new entries */	if (!rdp->curlist && rdp->nxtlist)		return 1; 	/* This cpu has finished callbacks to invoke */	if (rdp->donelist)		return 1; 	/* The rcu core waits for a quiescent state from the cpu */	if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)		return 1; 	/* nothing to do */	return 0;} /* * Check to see if there is any immediate RCU-related work to be done * by the current CPU, returning 1 if so.  This function is part of the * RCU implementation; it is -not- an exported member of the RCU API. */int rcu_pending(int cpu){	return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||		__rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));} /* * Check to see if any future RCU-related work will need to be done * by the current CPU, even if none need be done immediately, returning * 1 if so.  This function is part of the RCU implementation; it is -not- * an exported member of the RCU API. */int rcu_needs_cpu(int cpu){

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