/* * 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/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> /* Definition for rcupdate control block. */struct rcu_ctrlblk rcu_ctrlblk = 	{ .cur = -300, .completed = -300 };struct rcu_ctrlblk rcu_bh_ctrlblk =	{ .cur = -300, .completed = -300 }; /* Bookkeeping of the progress of the grace period */struct rcu_state {	spinlock_t	lock; /* Guard this struct and writes to rcu_ctrlblk */	cpumask_t	cpumask; /* CPUs that need to switch in order    */	                              /* for current batch to proceed.        */}; static struct rcu_state rcu_state ____cacheline_maxaligned_in_smp =	  {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE };static struct rcu_state rcu_bh_state ____cacheline_maxaligned_in_smp =	  {.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 maxbatch = 10; /** * 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;	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;	local_irq_restore(flags);} /* * 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;		if (++count >= maxbatch)			break;	}	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_state.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_state.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_state.lock. */static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp,				int next_pending){	if (next_pending)		rcp->next_pending = 1; 	if (rcp->next_pending &&			rcp->completed == rcp->cur) {		/* Can't change, since spin lock held. */		cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask); 		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++;	}} /* * 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, struct rcu_state *rsp){	cpu_clear(cpu, rsp->cpumask);	if (cpus_empty(rsp->cpumask)) {		/* batch completed ! */		rcp->completed = rcp->cur;		rcu_start_batch(rcp, rsp, 0);	}} /* * 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_state *rsp, 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(&rsp->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, rsp); 	spin_unlock(&rsp->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_state *rsp, 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(&rsp->lock);	if (rcp->cur != rcp->completed)		cpu_quiet(rdp->cpu, rcp, rsp);	spin_unlock_bh(&rsp->lock);	rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);	rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); }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, &rcu_state,					&per_cpu(rcu_data, cpu));	__rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk, &rcu_bh_state,					&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_state *rsp, 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;	} 	local_irq_disable();	if (rdp->nxtlist && !rdp->curlist) {		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(&rsp->lock);			rcu_start_batch(rcp, rsp, 1);			spin_unlock(&rsp->lock);		}	} else {		local_irq_enable();	}	rcu_check_quiescent_state(rcp, rsp, rdp);	if (rdp->donelist)		rcu_do_batch(rdp);} static void rcu_process_callbacks(unsigned long unused){	__rcu_process_callbacks(&rcu_ctrlblk, &rcu_state,				&__get_cpu_var(rcu_data));	__rcu_process_callbacks(&rcu_bh_ctrlblk, &rcu_bh_state,				&__get_cpu_var(rcu_bh_data));} void rcu_check_callbacks(int cpu, int user){	if (user || 	    (idle_cpu(cpu) && !in_softirq() && 				hardirq_count() <= (1 << HARDIRQ_SHIFT))) {		rcu_qsctr_inc(cpu);		rcu_bh_qsctr_inc(cpu);	} else if (!in_softirq())		rcu_bh_qsctr_inc(cpu);	tasklet_schedule(&per_cpu(rcu_tasklet, cpu));} static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,						struct rcu_data *rdp){	memset(rdp, 0, sizeof(*rdp));	rdp->curtail = &rdp->curlist;	rdp->nxttail = &rdp->nxtlist;	rdp->donetail = &rdp->donelist;	rdp->quiescbatch = rcp->completed;	rdp->qs_pending = 0;	rdp->cpu = cpu;} static void __devinit rcu_online_cpu(int cpu){	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);	struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu); 	rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);	rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);	tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);} static int __devinit rcu_cpu_notify(struct notifier_block *self, 				unsigned long action, void *hcpu){	long cpu = (long)hcpu;	switch (action) {	case CPU_UP_PREPARE:		rcu_online_cpu(cpu);		break;	case CPU_DEAD:		rcu_offline_cpu(cpu);		break;	default:		break;	}	return NOTIFY_OK;} static struct notifier_block __devinitdata rcu_nb = {	.notifier_call	= rcu_cpu_notify,}; /* * Initializes rcu mechanism.  Assumed to be called early. * That is before local timer(SMP) or jiffie timer (uniproc) is setup. * Note that rcu_qsctr and friends are implicitly * initialized due to the choice of ``0'' for RCU_CTR_INVALID. */void __init rcu_init(void){	rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,			(void *)(long)smp_processor_id());	/* Register notifier for non-boot CPUs */	register_cpu_notifier(&rcu_nb);} struct rcu_synchronize {	struct rcu_head head;	struct completion completion;}; /* Because of FASTCALL declaration of complete, we use this wrapper */static void wakeme_after_rcu(struct rcu_head  *head){	struct rcu_synchronize *rcu; 	rcu = container_of(head, struct rcu_synchronize, head);	complete(&rcu->completion);} /** * synchronize_rcu - wait until a grace period has elapsed. * * Control will return to the caller some time after a full grace * period has elapsed, 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. * * If your read-side code is not protected by rcu_read_lock(), do -not- * use synchronize_rcu(). */void synchronize_rcu(void){	struct rcu_synchronize rcu; 	init_completion(&rcu.completion);	/* Will wake me after RCU finished */	call_rcu(&rcu.head, wakeme_after_rcu); 	/* Wait for it */	wait_for_completion(&rcu.completion);} /* * Deprecated, use synchronize_rcu() or synchronize_sched() instead. */void synchronize_kernel(void){	synchronize_rcu();} module_param(maxbatch, int, 0);EXPORT_SYMBOL(call_rcu);  /* WARNING: GPL-only in April 2006. */EXPORT_SYMBOL(call_rcu_bh);  /* WARNING: GPL-only in April 2006. */EXPORT_SYMBOL_GPL(synchronize_rcu);EXPORT_SYMBOL(synchronize_kernel);  /* WARNING: GPL-only in April 2006. */