/* SPDX-License-Identifier: GPL-2.0+ *//* * Read-Copy Update mechanism for mutual exclusion (tree-based version) * Internal non-public definitions that provide either classic * or preemptible semantics. * * Copyright Red Hat, 2009 * Copyright IBM Corporation, 2009 * * Author: Ingo Molnar <mingo@elte.hu> *	   Paul E. McKenney <paulmck@linux.ibm.com> */ #include "../locking/rtmutex_common.h" #ifdef CONFIG_RCU_NOCB_CPUstatic cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */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 event 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 (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=%u.\n", NR_CPUS, nr_cpu_ids);#ifdef CONFIG_RCU_BOOST	pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",		kthread_prio, CONFIG_RCU_BOOST_DELAY);#endif	if (blimit != DEFAULT_RCU_BLIMIT)		pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);	if (qhimark != DEFAULT_RCU_QHIMARK)		pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);	if (qlowmark != DEFAULT_RCU_QLOMARK)		pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);	if (qovld != DEFAULT_RCU_QOVLD)		pr_info("\tBoot-time adjustment of callback overload level to %ld.\n", qovld);	if (jiffies_till_first_fqs != ULONG_MAX)		pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);	if (jiffies_till_next_fqs != ULONG_MAX)		pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);	if (jiffies_till_sched_qs != ULONG_MAX)		pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);	if (rcu_kick_kthreads)		pr_info("\tKick kthreads if too-long grace period.\n");	if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))		pr_info("\tRCU callback double-/use-after-free debug enabled.\n");	if (gp_preinit_delay)		pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);	if (gp_init_delay)		pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);	if (gp_cleanup_delay)		pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);	if (!use_softirq)		pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");	if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))		pr_info("\tRCU debug extended QS entry/exit.\n");	rcupdate_announce_bootup_oddness();} #ifdef CONFIG_PREEMPT_RCU static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);static void rcu_read_unlock_special(struct task_struct *t); /* * 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; 	raw_lockdep_assert_held_rcu_node(rnp);	WARN_ON_ONCE(rdp->mynode != rnp);	WARN_ON_ONCE(!rcu_is_leaf_node(rnp));	/* RCU better not be waiting on newly onlined CPUs! */	WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &		     rdp->grpmask); 	/*	 * 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)) {		WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry);		WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);	}	if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))		rnp->exp_tasks = &t->rcu_node_entry;	WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=		     !(rnp->qsmask & rdp->grpmask));	WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=		     !(rnp->expmask & rdp->grpmask));	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 && rdp->exp_deferred_qs)		rcu_report_exp_rdp(rdp);	else		WARN_ON_ONCE(rdp->exp_deferred_qs);} /* * Record a preemptible-RCU quiescent state for the specified CPU. * Note that this does not necessarily mean that the task currently running * on the CPU is in a quiescent state:  Instead, it means that the current * grace period need not wait on any RCU read-side critical section that * starts later on this CPU.  It also means that if the current task is * in an RCU read-side critical section, it has already added itself to * some leaf rcu_node structure's ->blkd_tasks list.  In addition to the * current task, there might be any number of other tasks blocked while * in an RCU read-side critical section. * * Callers to this function must disable preemption. */static void rcu_qs(void){	RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");	if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {		trace_rcu_grace_period(TPS("rcu_preempt"),				       __this_cpu_read(rcu_data.gp_seq),				       TPS("cpuqs"));		__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);		barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */		WRITE_ONCE(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. */void rcu_note_context_switch(bool preempt){	struct task_struct *t = current;	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);	struct rcu_node *rnp; 	trace_rcu_utilization(TPS("Start context switch"));	lockdep_assert_irqs_disabled();	WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0);	if (rcu_preempt_depth() > 0 &&	    !t->rcu_read_unlock_special.b.blocked) { 		/* Possibly blocking in an RCU read-side critical section. */		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(rcu_state.name,				       t->pid,				       (rnp->qsmask & rdp->grpmask)				       ? rnp->gp_seq				       : rcu_seq_snap(&rnp->gp_seq));		rcu_preempt_ctxt_queue(rnp, rdp);	} else {		rcu_preempt_deferred_qs(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_qs();	if (rdp->exp_deferred_qs)		rcu_report_exp_rdp(rdp);	trace_rcu_utilization(TPS("End context switch"));}EXPORT_SYMBOL_GPL(rcu_note_context_switch); /* * 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 READ_ONCE(rnp->gp_tasks) != NULL;} /* Bias and limit values for ->rcu_read_lock_nesting. */#define RCU_NEST_BIAS INT_MAX#define RCU_NEST_NMAX (-INT_MAX / 2)#define RCU_NEST_PMAX (INT_MAX / 2) static void rcu_preempt_read_enter(void){	current->rcu_read_lock_nesting++;} static void rcu_preempt_read_exit(void){	current->rcu_read_lock_nesting--;} static void rcu_preempt_depth_set(int val){	current->rcu_read_lock_nesting = val;} /* * Preemptible 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){	rcu_preempt_read_enter();	if (IS_ENABLED(CONFIG_PROVE_LOCKING))		WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);	barrier();  /* critical section after entry code. */}EXPORT_SYMBOL_GPL(__rcu_read_lock); /* * Preemptible 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; 	if (rcu_preempt_depth() != 1) {		rcu_preempt_read_exit();	} else {		barrier();  /* critical section before exit code. */		rcu_preempt_depth_set(-RCU_NEST_BIAS);		barrier();  /* assign before ->rcu_read_unlock_special load */		if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))			rcu_read_unlock_special(t);		barrier();  /* ->rcu_read_unlock_special load before assign */		rcu_preempt_depth_set(0);	}	if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {		int rrln = rcu_preempt_depth(); 		WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX);	}}EXPORT_SYMBOL_GPL(__rcu_read_unlock); /* * 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);} /* * Report deferred quiescent states.  The deferral time can * be quite short, for example, in the case of the call from * rcu_read_unlock_special(). */static voidrcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags){	bool empty_exp;	bool empty_norm;	bool empty_exp_now;	struct list_head *np;	bool drop_boost_mutex = false;	struct rcu_data *rdp;	struct rcu_node *rnp;	union rcu_special special; 	/*	 * 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;	rdp = this_cpu_ptr(&rcu_data);	if (!special.s && !rdp->exp_deferred_qs) {		local_irq_restore(flags);		return;	}	t->rcu_read_unlock_special.s = 0;	if (special.b.need_qs)		rcu_qs(); 	/*	 * Respond to a request by an expedited grace period for a	 * quiescent state from this CPU.  Note that requests from	 * tasks are handled when removing the task from the	 * blocked-tasks list below.	 */	if (rdp->exp_deferred_qs)		rcu_report_exp_rdp(rdp); 	/* Clean up if blocked during RCU read-side critical section. */	if (special.b.blocked) { 		/*		 * 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);		WARN_ON_ONCE(!rcu_is_leaf_node(rnp));		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);		WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&			     (!empty_norm || rnp->qsmask));		empty_exp = sync_rcu_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->gp_seq, t->pid);		if (&t->rcu_node_entry == rnp->gp_tasks)

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