/* * Read-Copy Update mechanism for mutual exclusion (tree-based version) * Internal non-public definitions that provide either classic * or preemptible 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, you can access it online at * http://www.gnu.org/licenses/gpl-2.0.html. * * 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/gfp.h>#include <linux/oom.h>#include <linux/smpboot.h>#include "../time/tick-internal.h" #ifdef CONFIG_RCU_BOOST #include "../locking/rtmutex_common.h" /* * Control variables for per-CPU and per-rcu_node kthreads.  These * handle all flavors of RCU. */static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);DEFINE_PER_CPU(char, rcu_cpu_has_work); #else /* #ifdef CONFIG_RCU_BOOST */ /* * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST, * all uses are in dead code.  Provide a definition to keep the compiler * happy, but add WARN_ON_ONCE() to complain if used in the wrong place. * This probably needs to be excluded from -rt builds. */#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; }) #endif /* #else #ifdef CONFIG_RCU_BOOST */ #ifdef CONFIG_RCU_NOCB_CPUstatic cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */static bool have_rcu_nocb_mask;	    /* Was rcu_nocb_mask allocated? */static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ /* * Check the RCU kernel configuration parameters and print informative * messages about anything out of the ordinary. */static void __init rcu_bootup_announce_oddness(void){	if (IS_ENABLED(CONFIG_RCU_TRACE))		pr_info("\tRCU debugfs-based tracing is enabled.\n");	if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||	    (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))		pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",		       RCU_FANOUT);	if (rcu_fanout_exact)		pr_info("\tHierarchical RCU autobalancing is disabled.\n");	if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))		pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");	if (IS_ENABLED(CONFIG_PROVE_RCU))		pr_info("\tRCU lockdep checking is enabled.\n");	if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE))		pr_info("\tRCU torture testing starts during boot.\n");	if (RCU_NUM_LVLS >= 4)		pr_info("\tFour(or more)-level hierarchy is enabled.\n");	if (RCU_FANOUT_LEAF != 16)		pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",			RCU_FANOUT_LEAF);	if (rcu_fanout_leaf != RCU_FANOUT_LEAF)		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);	if (nr_cpu_ids != NR_CPUS)		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);	if (IS_ENABLED(CONFIG_RCU_BOOST))		pr_info("\tRCU kthread priority: %d.\n", kthread_prio);} #ifdef CONFIG_PREEMPT_RCU RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);static struct rcu_state *const rcu_state_p = &rcu_preempt_state;static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data; static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,			       bool wake); /* * Tell them what RCU they are running. */static void __init rcu_bootup_announce(void){	pr_info("Preemptible hierarchical RCU implementation.\n");	rcu_bootup_announce_oddness();} /* Flags for rcu_preempt_ctxt_queue() decision table. */#define RCU_GP_TASKS	0x8#define RCU_EXP_TASKS	0x4#define RCU_GP_BLKD	0x2#define RCU_EXP_BLKD	0x1 /* * Queues a task preempted within an RCU-preempt read-side critical * section into the appropriate location within the ->blkd_tasks list, * depending on the states of any ongoing normal and expedited grace * periods.  The ->gp_tasks pointer indicates which element the normal * grace period is waiting on (NULL if none), and the ->exp_tasks pointer * indicates which element the expedited grace period is waiting on (again, * NULL if none).  If a grace period is waiting on a given element in the * ->blkd_tasks list, it also waits on all subsequent elements.  Thus, * adding a task to the tail of the list blocks any grace period that is * already waiting on one of the elements.  In contrast, adding a task * to the head of the list won't block any grace period that is already * waiting on one of the elements. * * This queuing is imprecise, and can sometimes make an ongoing grace * period wait for a task that is not strictly speaking blocking it. * Given the choice, we needlessly block a normal grace period rather than * blocking an expedited grace period. * * Note that an endless sequence of expedited grace periods still cannot * indefinitely postpone a normal grace period.  Eventually, all of the * fixed number of preempted tasks blocking the normal grace period that are * not also blocking the expedited grace period will resume and complete * their RCU read-side critical sections.  At that point, the ->gp_tasks * pointer will equal the ->exp_tasks pointer, at which point the end of * the corresponding expedited grace period will also be the end of the * normal grace period. */static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)	__releases(rnp->lock) /* But leaves rrupts disabled. */{	int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +			 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +			 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +			 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);	struct task_struct *t = current; 	/*	 * Decide where to queue the newly blocked task.  In theory,	 * this could be an if-statement.  In practice, when I tried	 * that, it was quite messy.	 */	switch (blkd_state) {	case 0:	case                RCU_EXP_TASKS:	case                RCU_EXP_TASKS + RCU_GP_BLKD:	case RCU_GP_TASKS:	case RCU_GP_TASKS + RCU_EXP_TASKS: 		/*		 * Blocking neither GP, or first task blocking the normal		 * GP but not blocking the already-waiting expedited GP.		 * Queue at the head of the list to avoid unnecessarily		 * blocking the already-waiting GPs.		 */		list_add(&t->rcu_node_entry, &rnp->blkd_tasks);		break; 	case                                              RCU_EXP_BLKD:	case                                RCU_GP_BLKD:	case                                RCU_GP_BLKD + RCU_EXP_BLKD:	case RCU_GP_TASKS +                               RCU_EXP_BLKD:	case RCU_GP_TASKS +                 RCU_GP_BLKD + RCU_EXP_BLKD:	case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: 		/*		 * First task arriving that blocks either GP, or first task		 * arriving that blocks the expedited GP (with the normal		 * GP already waiting), or a task arriving that blocks		 * both GPs with both GPs already waiting.  Queue at the		 * tail of the list to avoid any GP waiting on any of the		 * already queued tasks that are not blocking it.		 */		list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);		break; 	case                RCU_EXP_TASKS +               RCU_EXP_BLKD:	case                RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:	case RCU_GP_TASKS + RCU_EXP_TASKS +               RCU_EXP_BLKD: 		/*		 * Second or subsequent task blocking the expedited GP.		 * The task either does not block the normal GP, or is the		 * first task blocking the normal GP.  Queue just after		 * the first task blocking the expedited GP.		 */		list_add(&t->rcu_node_entry, rnp->exp_tasks);		break; 	case RCU_GP_TASKS +                 RCU_GP_BLKD:	case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD: 		/*		 * Second or subsequent task blocking the normal GP.		 * The task does not block the expedited GP. Queue just		 * after the first task blocking the normal GP.		 */		list_add(&t->rcu_node_entry, rnp->gp_tasks);		break; 	default: 		/* Yet another exercise in excessive paranoia. */		WARN_ON_ONCE(1);		break;	} 	/*	 * We have now queued the task.  If it was the first one to	 * block either grace period, update the ->gp_tasks and/or	 * ->exp_tasks pointers, respectively, to reference the newly	 * blocked tasks.	 */	if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))		rnp->gp_tasks = &t->rcu_node_entry;	if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))		rnp->exp_tasks = &t->rcu_node_entry;	raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */ 	/*	 * Report the quiescent state for the expedited GP.  This expedited	 * GP should not be able to end until we report, so there should be	 * no need to check for a subsequent expedited GP.  (Though we are	 * still in a quiescent state in any case.)	 */	if (blkd_state & RCU_EXP_BLKD &&	    t->rcu_read_unlock_special.b.exp_need_qs) {		t->rcu_read_unlock_special.b.exp_need_qs = false;		rcu_report_exp_rdp(rdp->rsp, rdp, true);	} else {		WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);	}} /* * Record a preemptible-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. * * As with the other rcu_*_qs() functions, callers to this function * must disable preemption. */static void rcu_preempt_qs(void){	if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {		trace_rcu_grace_period(TPS("rcu_preempt"),				       __this_cpu_read(rcu_data_p->gpnum),				       TPS("cpuqs"));		__this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);		barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */		current->rcu_read_unlock_special.b.need_qs = false;	}} /* * 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 blkd_tasks list. * 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 blkd_tasks list entries * predating the current grace period drain, in other words, until * rnp->gp_tasks becomes NULL. * * Caller must disable interrupts. */static void rcu_preempt_note_context_switch(void){	struct task_struct *t = current;	struct rcu_data *rdp;	struct rcu_node *rnp; 	if (t->rcu_read_lock_nesting > 0 &&	    !t->rcu_read_unlock_special.b.blocked) { 		/* Possibly blocking in an RCU read-side critical section. */		rdp = this_cpu_ptr(rcu_state_p->rda);		rnp = rdp->mynode;		raw_spin_lock_rcu_node(rnp);		t->rcu_read_unlock_special.b.blocked = true;		t->rcu_blocked_node = rnp; 		/*		 * Verify the CPU's sanity, trace the preemption, and		 * then queue the task as required based on the states		 * of any ongoing and expedited grace periods.		 */		WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));		trace_rcu_preempt_task(rdp->rsp->name,				       t->pid,				       (rnp->qsmask & rdp->grpmask)				       ? rnp->gpnum				       : rnp->gpnum + 1);		rcu_preempt_ctxt_queue(rnp, rdp);	} else if (t->rcu_read_lock_nesting < 0 &&		   t->rcu_read_unlock_special.s) { 		/*		 * Complete exit from RCU read-side critical section on		 * behalf of preempted instance of __rcu_read_unlock().		 */		rcu_read_unlock_special(t);	} 	/*	 * 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();} /* * 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_preempt_blocked_readers_cgp(struct rcu_node *rnp){	return rnp->gp_tasks != NULL;} /* * Advance a ->blkd_tasks-list pointer to the next entry, instead * returning NULL if at the end of the list. */static struct list_head *rcu_next_node_entry(struct task_struct *t,					     struct rcu_node *rnp){	struct list_head *np; 	np = t->rcu_node_entry.next;	if (np == &rnp->blkd_tasks)		np = NULL;	return np;} /* * Return true if the specified rcu_node structure has tasks that were * preempted within an RCU read-side critical section. */static bool rcu_preempt_has_tasks(struct rcu_node *rnp){	return !list_empty(&rnp->blkd_tasks);} /* * 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. */void rcu_read_unlock_special(struct task_struct *t){	bool empty_exp;	bool empty_norm;	bool empty_exp_now;	unsigned long flags;	struct list_head *np;	bool drop_boost_mutex = false;	struct rcu_data *rdp;	struct rcu_node *rnp;	union rcu_special 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 its critical section,	 * report the fact that it has exited.  Because irqs are disabled,	 * t->rcu_read_unlock_special cannot change.	 */	special = t->rcu_read_unlock_special;	if (special.b.need_qs) {		rcu_preempt_qs();		t->rcu_read_unlock_special.b.need_qs = false;		if (!t->rcu_read_unlock_special.s) {			local_irq_restore(flags);			return;		}	} 	/*	 * Respond to a request for an expedited grace period, but only if	 * we were not preempted, meaning that we were running on the same	 * CPU throughout.  If we were preempted, the exp_need_qs flag	 * would have been cleared at the time of the first preemption,	 * and the quiescent state would be reported when we were dequeued.	 */	if (special.b.exp_need_qs) {		WARN_ON_ONCE(special.b.blocked);		t->rcu_read_unlock_special.b.exp_need_qs = false;		rdp = this_cpu_ptr(rcu_state_p->rda);		rcu_report_exp_rdp(rcu_state_p, rdp, true);		if (!t->rcu_read_unlock_special.s) {			local_irq_restore(flags);			return;		}	} 	/* Hardware IRQ handlers cannot block, complain if they get here. */	if (in_irq() || in_serving_softirq()) {		lockdep_rcu_suspicious(__FILE__, __LINE__,				       "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");		pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",			 t->rcu_read_unlock_special.s,			 t->rcu_read_unlock_special.b.blocked,			 t->rcu_read_unlock_special.b.exp_need_qs,			 t->rcu_read_unlock_special.b.need_qs);		local_irq_restore(flags);		return;	} 	/* Clean up if blocked during RCU read-side critical section. */	if (special.b.blocked) {		t->rcu_read_unlock_special.b.blocked = false; 		/*		 * Remove this task from the list it blocked on.  The task		 * now remains queued on the rcu_node corresponding to the		 * CPU it first blocked on, so there is no longer any need		 * to loop.  Retain a WARN_ON_ONCE() out of sheer paranoia.		 */		rnp = t->rcu_blocked_node;		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */		WARN_ON_ONCE(rnp != t->rcu_blocked_node);		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);		empty_exp = sync_rcu_preempt_exp_done(rnp);		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */		np = rcu_next_node_entry(t, rnp);		list_del_init(&t->rcu_node_entry);		t->rcu_blocked_node = NULL;		trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),						rnp->gpnum, t->pid);		if (&t->rcu_node_entry == rnp->gp_tasks)			rnp->gp_tasks = np;		if (&t->rcu_node_entry == rnp->exp_tasks)			rnp->exp_tasks = np;		if (IS_ENABLED(CONFIG_RCU_BOOST)) {			if (&t->rcu_node_entry == rnp->boost_tasks)				rnp->boost_tasks = np;			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;		} 		/*		 * 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,		 * so we must take a snapshot of the expedited state.		 */		empty_exp_now = sync_rcu_preempt_exp_done(rnp);		if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {			trace_rcu_quiescent_state_report(TPS("preempt_rcu"),							 rnp->gpnum,							 0, rnp->qsmask,							 rnp->level,							 rnp->grplo,							 rnp->grphi,							 !!rnp->gp_tasks);			rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);		} else {			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);		} 		/* Unboost if we were boosted. */		if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)			rt_mutex_unlock(&rnp->boost_mtx); 		/*		 * If this was the last task on the expedited lists,

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