/* * Read-Copy Update mechanism for mutual exclusion (tree-based version) * Internal non-public definitions that provide either classic * or preemptable semantics. * * 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 Red Hat, 2009 * Copyright IBM Corporation, 2009 * * Author: Ingo Molnar <mingo@elte.hu> *	   Paul E. McKenney <paulmck@linux.vnet.ibm.com> */ #include <linux/delay.h>#include <linux/stop_machine.h> /* * Check the RCU kernel configuration parameters and print informative * messages about anything out of the ordinary.  If you like #ifdef, you * will love this function. */static void __init rcu_bootup_announce_oddness(void){#ifdef CONFIG_RCU_TRACE	printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");#endif#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)	printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",	       CONFIG_RCU_FANOUT);#endif#ifdef CONFIG_RCU_FANOUT_EXACT	printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");#endif#ifdef CONFIG_RCU_FAST_NO_HZ	printk(KERN_INFO	       "\tRCU dyntick-idle grace-period acceleration is enabled.\n");#endif#ifdef CONFIG_PROVE_RCU	printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");#endif#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE	printk(KERN_INFO "\tRCU torture testing starts during boot.\n");#endif#ifndef CONFIG_RCU_CPU_STALL_DETECTOR	printk(KERN_INFO	       "\tRCU-based detection of stalled CPUs is disabled.\n");#endif#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)	printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n");#endif#if NUM_RCU_LVL_4 != 0	printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n");#endif} #ifdef CONFIG_TREE_PREEMPT_RCU struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); static int rcu_preempted_readers_exp(struct rcu_node *rnp); /* * Tell them what RCU they are running. */static void __init rcu_bootup_announce(void){	printk(KERN_INFO "Preemptable hierarchical RCU implementation.\n");	rcu_bootup_announce_oddness();} /* * Return the number of RCU-preempt batches processed thus far * for debug and statistics. */long rcu_batches_completed_preempt(void){	return rcu_preempt_state.completed;}EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); /* * Return the number of RCU batches processed thus far for debug & stats. */long rcu_batches_completed(void){	return rcu_batches_completed_preempt();}EXPORT_SYMBOL_GPL(rcu_batches_completed); /* * Force a quiescent state for preemptible RCU. */void rcu_force_quiescent_state(void){	force_quiescent_state(&rcu_preempt_state, 0);}EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); /* * Record a preemptable-RCU quiescent state for the specified CPU.  Note * that this just means that the task currently running on the CPU is * not in a quiescent state.  There might be any number of tasks blocked * while in an RCU read-side critical section. * * Unlike the other rcu_*_qs() functions, callers to this function * must disable irqs in order to protect the assignment to * ->rcu_read_unlock_special. */static void rcu_preempt_qs(int cpu){	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); 	rdp->passed_quiesc_completed = rdp->gpnum - 1;	barrier();	rdp->passed_quiesc = 1;	current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;} /* * We have entered the scheduler, and the current task might soon be * context-switched away from.  If this task is in an RCU read-side * critical section, we will no longer be able to rely on the CPU to * record that fact, so we enqueue the task on the appropriate entry * of the blocked_tasks[] array.  The task will dequeue itself when * it exits the outermost enclosing RCU read-side critical section. * Therefore, the current grace period cannot be permitted to complete * until the blocked_tasks[] entry indexed by the low-order bit of * rnp->gpnum empties. * * Caller must disable preemption. */static void rcu_preempt_note_context_switch(int cpu){	struct task_struct *t = current;	unsigned long flags;	int phase;	struct rcu_data *rdp;	struct rcu_node *rnp; 	if (t->rcu_read_lock_nesting &&	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { 		/* Possibly blocking in an RCU read-side critical section. */		rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);		rnp = rdp->mynode;		raw_spin_lock_irqsave(&rnp->lock, flags);		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;		t->rcu_blocked_node = rnp; 		/*		 * If this CPU has already checked in, then this task		 * will hold up the next grace period rather than the		 * current grace period.  Queue the task accordingly.		 * If the task is queued for the current grace period		 * (i.e., this CPU has not yet passed through a quiescent		 * state for the current grace period), then as long		 * as that task remains queued, the current grace period		 * cannot end.		 *		 * But first, note that the current CPU must still be		 * on line!		 */		WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));		phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1;		list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);		raw_spin_unlock_irqrestore(&rnp->lock, flags);	} 	/*	 * Either we were not in an RCU read-side critical section to	 * begin with, or we have now recorded that critical section	 * globally.  Either way, we can now note a quiescent state	 * for this CPU.  Again, if we were in an RCU read-side critical	 * section, and if that critical section was blocking the current	 * grace period, then the fact that the task has been enqueued	 * means that we continue to block the current grace period.	 */	local_irq_save(flags);	rcu_preempt_qs(cpu);	local_irq_restore(flags);} /* * Tree-preemptable 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();  /* needed if we ever invoke rcu_read_lock in rcutree.c */}EXPORT_SYMBOL_GPL(__rcu_read_lock); /* * Check for preempted RCU readers blocking the current grace period * for the specified rcu_node structure.  If the caller needs a reliable * answer, it must hold the rcu_node's ->lock. */static int rcu_preempted_readers(struct rcu_node *rnp){	int phase = rnp->gpnum & 0x1; 	return !list_empty(&rnp->blocked_tasks[phase]) ||	       !list_empty(&rnp->blocked_tasks[phase + 2]);} /* * Record a quiescent state for all tasks that were previously queued * on the specified rcu_node structure and that were blocking the current * RCU grace period.  The caller must hold the specified rnp->lock with * irqs disabled, and this lock is released upon return, but irqs remain * disabled. */static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)	__releases(rnp->lock){	unsigned long mask;	struct rcu_node *rnp_p; 	if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {		raw_spin_unlock_irqrestore(&rnp->lock, flags);		return;  /* Still need more quiescent states! */	} 	rnp_p = rnp->parent;	if (rnp_p == NULL) {		/*		 * Either there is only one rcu_node in the tree,		 * or tasks were kicked up to root rcu_node due to		 * CPUs going offline.		 */		rcu_report_qs_rsp(&rcu_preempt_state, flags);		return;	} 	/* Report up the rest of the hierarchy. */	mask = rnp->grpmask;	raw_spin_unlock(&rnp->lock);	/* irqs remain disabled. */	raw_spin_lock(&rnp_p->lock);	/* irqs already disabled. */	rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);} /* * Handle special cases during rcu_read_unlock(), such as needing to * notify RCU core processing or task having blocked during the RCU * read-side critical section. */static void rcu_read_unlock_special(struct task_struct *t){	int empty;	int empty_exp;	unsigned long flags;	struct rcu_node *rnp;	int special; 	/* NMI handlers cannot block and cannot safely manipulate state. */	if (in_nmi())		return; 	local_irq_save(flags); 	/*	 * If RCU core is waiting for this CPU to exit critical section,	 * let it know that we have done so.	 */	special = t->rcu_read_unlock_special;	if (special & RCU_READ_UNLOCK_NEED_QS) {		rcu_preempt_qs(smp_processor_id());	} 	/* Hardware IRQ handlers cannot block. */	if (in_irq()) {		local_irq_restore(flags);		return;	} 	/* Clean up if blocked during RCU read-side critical section. */	if (special & RCU_READ_UNLOCK_BLOCKED) {		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; 		/*		 * Remove this task from the list it blocked on.  The		 * task can migrate while we acquire the lock, but at		 * most one time.  So at most two passes through loop.		 */		for (;;) {			rnp = t->rcu_blocked_node;			raw_spin_lock(&rnp->lock);  /* irqs already disabled. */			if (rnp == t->rcu_blocked_node)				break;			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */		}		empty = !rcu_preempted_readers(rnp);		empty_exp = !rcu_preempted_readers_exp(rnp);		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */		list_del_init(&t->rcu_node_entry);		t->rcu_blocked_node = NULL; 		/*		 * If this was the last task on the current list, and if		 * we aren't waiting on any CPUs, report the quiescent state.		 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock.		 */		if (empty)			raw_spin_unlock_irqrestore(&rnp->lock, flags);		else			rcu_report_unblock_qs_rnp(rnp, flags); 		/*		 * If this was the last task on the expedited lists,		 * then we need to report up the rcu_node hierarchy.		 */		if (!empty_exp && !rcu_preempted_readers_exp(rnp))			rcu_report_exp_rnp(&rcu_preempt_state, rnp);	} else {		local_irq_restore(flags);	}} /* * Tree-preemptable 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; 	barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */	--t->rcu_read_lock_nesting;	barrier();  /* decrement before load of ->rcu_read_unlock_special */	if (t->rcu_read_lock_nesting == 0 &&	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))		rcu_read_unlock_special(t);#ifdef CONFIG_PROVE_LOCKING	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);#endif /* #ifdef CONFIG_PROVE_LOCKING */}EXPORT_SYMBOL_GPL(__rcu_read_unlock); #ifdef CONFIG_RCU_CPU_STALL_DETECTOR #ifdef CONFIG_RCU_CPU_STALL_VERBOSE /* * Dump detailed information for all tasks blocking the current RCU * grace period on the specified rcu_node structure. */static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp){	unsigned long flags;	struct list_head *lp;	int phase;	struct task_struct *t; 	if (rcu_preempted_readers(rnp)) {		raw_spin_lock_irqsave(&rnp->lock, flags);		phase = rnp->gpnum & 0x1;		lp = &rnp->blocked_tasks[phase];		list_for_each_entry(t, lp, rcu_node_entry)			sched_show_task(t);		raw_spin_unlock_irqrestore(&rnp->lock, flags);	}} /* * Dump detailed information for all tasks blocking the current RCU * grace period. */static void rcu_print_detail_task_stall(struct rcu_state *rsp){	struct rcu_node *rnp = rcu_get_root(rsp); 	rcu_print_detail_task_stall_rnp(rnp);	rcu_for_each_leaf_node(rsp, rnp)		rcu_print_detail_task_stall_rnp(rnp);} #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ static void rcu_print_detail_task_stall(struct rcu_state *rsp){} #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ /* * Scan the current list of tasks blocked within RCU read-side critical * sections, printing out the tid of each. */static void rcu_print_task_stall(struct rcu_node *rnp){	struct list_head *lp;	int phase;	struct task_struct *t; 	if (rcu_preempted_readers(rnp)) {		phase = rnp->gpnum & 0x1;		lp = &rnp->blocked_tasks[phase];		list_for_each_entry(t, lp, rcu_node_entry)			printk(" P%d", t->pid);	}} /* * Suppress preemptible RCU's CPU stall warnings by pushing the * time of the next stall-warning message comfortably far into the * future. */static void rcu_preempt_stall_reset(void){	rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;} #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ /* * Check that the list of blocked tasks for the newly completed grace * period is in fact empty.  It is a serious bug to complete a grace * period that still has RCU readers blocked!  This function must be * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock * must be held by the caller. */static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp){	WARN_ON_ONCE(rcu_preempted_readers(rnp));	WARN_ON_ONCE(rnp->qsmask);} #ifdef CONFIG_HOTPLUG_CPU /* * Handle tasklist migration for case in which all CPUs covered by the * specified rcu_node have gone offline.  Move them up to the root * rcu_node.  The reason for not just moving them to the immediate * parent is to remove the need for rcu_read_unlock_special() to * make more than two attempts to acquire the target rcu_node's lock. * Returns true if there were tasks blocking the current RCU grace * period. * * Returns 1 if there was previously a task blocking the current grace * period on the specified rcu_node structure. * * The caller must hold rnp->lock with irqs disabled. */static int rcu_preempt_offline_tasks(struct rcu_state *rsp,				     struct rcu_node *rnp,				     struct rcu_data *rdp){	int i;	struct list_head *lp;	struct list_head *lp_root;	int retval = 0;	struct rcu_node *rnp_root = rcu_get_root(rsp);	struct task_struct *tp; 	if (rnp == rnp_root) {		WARN_ONCE(1, "Last CPU thought to be offlined?");		return 0;  /* Shouldn't happen: at least one CPU online. */	}	WARN_ON_ONCE(rnp != rdp->mynode &&		     (!list_empty(&rnp->blocked_tasks[0]) ||		      !list_empty(&rnp->blocked_tasks[1]) ||		      !list_empty(&rnp->blocked_tasks[2]) ||		      !list_empty(&rnp->blocked_tasks[3]))); 	/*	 * Move tasks up to root rcu_node.  Rely on the fact that the	 * root rcu_node can be at most one ahead of the rest of the	 * rcu_nodes in terms of gp_num value.  This fact allows us to	 * move the blocked_tasks[] array directly, element by element.	 */	if (rcu_preempted_readers(rnp))		retval |= RCU_OFL_TASKS_NORM_GP;	if (rcu_preempted_readers_exp(rnp))		retval |= RCU_OFL_TASKS_EXP_GP;	for (i = 0; i < 4; i++) {		lp = &rnp->blocked_tasks[i];		lp_root = &rnp_root->blocked_tasks[i];		while (!list_empty(lp)) {			tp = list_entry(lp->next, typeof(*tp), rcu_node_entry);			raw_spin_lock(&rnp_root->lock); /* irqs already disabled */

Lines 1–500 of 1262. Load more