/* * 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> */  #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); /* * Tell them what RCU they are running. */static inline void rcu_bootup_announce(void){	printk(KERN_INFO	       "Experimental preemptable hierarchical RCU implementation.\n");} /* * 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); /* * 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. */static void rcu_preempt_qs(int cpu){	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);	rdp->passed_quiesc_completed = rdp->completed;	barrier();	rdp->passed_quiesc = 1;} /* * 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 = rcu_preempt_state.rda[cpu];		rnp = rdp->mynode;		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]);		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.	 */	rcu_preempt_qs(cpu);	local_irq_save(flags);	t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;	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){	ACCESS_ONCE(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){	return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);} static void rcu_read_unlock_special(struct task_struct *t){	int empty;	unsigned long flags;	unsigned long mask;	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) {		t->rcu_read_unlock_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;			spin_lock(&rnp->lock);  /* irqs already disabled. */			if (rnp == t->rcu_blocked_node)				break;			spin_unlock(&rnp->lock);  /* irqs remain disabled. */		}		empty = !rcu_preempted_readers(rnp);		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 both cpu_quiet_msk_finish() and cpu_quiet_msk()		 * drop rnp->lock and restore irq.		 */		if (!empty && rnp->qsmask == 0 &&		    !rcu_preempted_readers(rnp)) {			struct rcu_node *rnp_p; 			if (rnp->parent == NULL) {				/* Only one rcu_node in the tree. */				cpu_quiet_msk_finish(&rcu_preempt_state, flags);				return;			}			/* Report up the rest of the hierarchy. */			mask = rnp->grpmask;			spin_unlock_irqrestore(&rnp->lock, flags);			rnp_p = rnp->parent;			spin_lock_irqsave(&rnp_p->lock, flags);			WARN_ON_ONCE(rnp->qsmask);			cpu_quiet_msk(mask, &rcu_preempt_state, rnp_p, flags);			return;		}		spin_unlock(&rnp->lock);	}	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 */	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))		rcu_read_unlock_special(t);}EXPORT_SYMBOL_GPL(__rcu_read_unlock); #ifdef CONFIG_RCU_CPU_STALL_DETECTOR /* * 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){	unsigned long flags;	struct list_head *lp;	int phase;	struct task_struct *t; 	if (rcu_preempted_readers(rnp)) {		spin_lock_irqsave(&rnp->lock, flags);		phase = rnp->gpnum & 0x1;		lp = &rnp->blocked_tasks[phase];		list_for_each_entry(t, lp, rcu_node_entry)			printk(" P%d", t->pid);		spin_unlock_irqrestore(&rnp->lock, flags);	}} #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 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 = rcu_preempted_readers(rnp);	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]))); 	/*	 * 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.	 */	for (i = 0; i < 2; 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);			spin_lock(&rnp_root->lock); /* irqs already disabled */			list_del(&tp->rcu_node_entry);			tp->rcu_blocked_node = rnp_root;			list_add(&tp->rcu_node_entry, lp_root);			spin_unlock(&rnp_root->lock); /* irqs remain disabled */		}	} 	return retval;} /* * Do CPU-offline processing for preemptable RCU. */static void rcu_preempt_offline_cpu(int cpu){	__rcu_offline_cpu(cpu, &rcu_preempt_state);} #endif /* #ifdef CONFIG_HOTPLUG_CPU */ /* * Check for a quiescent state from the current CPU.  When a task blocks, * the task is recorded in the corresponding CPU's rcu_node structure, * which is checked elsewhere. * * Caller must disable hard irqs. */static void rcu_preempt_check_callbacks(int cpu){	struct task_struct *t = current; 	if (t->rcu_read_lock_nesting == 0) {		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;		rcu_preempt_qs(cpu);		return;	}	if (per_cpu(rcu_preempt_data, cpu).qs_pending)		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;} /* * Process callbacks for preemptable RCU. */static void rcu_preempt_process_callbacks(void){	__rcu_process_callbacks(&rcu_preempt_state,				&__get_cpu_var(rcu_preempt_data));} /* * Queue a preemptable-RCU callback for invocation after a grace period. */void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)){	__call_rcu(head, func, &rcu_preempt_state);}EXPORT_SYMBOL_GPL(call_rcu); /* * Wait for an rcu-preempt grace period.  We are supposed to expedite the * grace period, but this is the crude slow compatability hack, so just * invoke synchronize_rcu(). */void synchronize_rcu_expedited(void){	synchronize_rcu();}EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); /* * Check to see if there is any immediate preemptable-RCU-related work * to be done. */static int rcu_preempt_pending(int cpu){	return __rcu_pending(&rcu_preempt_state,			     &per_cpu(rcu_preempt_data, cpu));} /* * Does preemptable RCU need the CPU to stay out of dynticks mode? */static int rcu_preempt_needs_cpu(int cpu){	return !!per_cpu(rcu_preempt_data, cpu).nxtlist;} /** * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. */void rcu_barrier(void){	_rcu_barrier(&rcu_preempt_state, call_rcu);}EXPORT_SYMBOL_GPL(rcu_barrier); /* * Initialize preemptable RCU's per-CPU data. */static void __cpuinit rcu_preempt_init_percpu_data(int cpu){	rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);} /* * Move preemptable RCU's callbacks to ->orphan_cbs_list. */static void rcu_preempt_send_cbs_to_orphanage(void){	rcu_send_cbs_to_orphanage(&rcu_preempt_state);} /* * Initialize preemptable RCU's state structures. */static void __init __rcu_init_preempt(void){	RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);} /* * Check for a task exiting while in a preemptable-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 (t->rcu_read_lock_nesting == 0)		return;	t->rcu_read_lock_nesting = 1;	rcu_read_unlock();} #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ /* * Tell them what RCU they are running. */static inline void rcu_bootup_announce(void){	printk(KERN_INFO "Hierarchical RCU implementation.\n");} /* * Return the number of RCU batches processed thus far for debug & stats. */long rcu_batches_completed(void){	return rcu_batches_completed_sched();}EXPORT_SYMBOL_GPL(rcu_batches_completed); /* * Because preemptable RCU does not exist, we never have to check for * CPUs being in quiescent states.

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