v4.19.13 snapshot.
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
new file mode 100644
index 0000000..a97c20e
--- /dev/null
+++ b/kernel/rcu/tree_plugin.h
@@ -0,0 +1,2692 @@
+/*
+ * 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/sched/debug.h>
+#include <linux/smpboot.h>
+#include <linux/sched/isolation.h>
+#include <uapi/linux/sched/types.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; })
+#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
+#ifdef CONFIG_RCU_NOCB_CPU
+static 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 (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 (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 (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
+ pr_info("\tRCU debug extended QS entry/exit.\n");
+ rcupdate_announce_bootup_oddness();
+}
+
+#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);
+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)) {
+ 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 &&
+ 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 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_preempt_qs(void)
+{
+ RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n");
+ if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
+ trace_rcu_grace_period(TPS("rcu_preempt"),
+ __this_cpu_read(rcu_data_p->gp_seq),
+ 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(bool preempt)
+{
+ struct task_struct *t = current;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+
+ lockdep_assert_irqs_disabled();
+ WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
+ 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->gp_seq
+ : rcu_seq_snap(&rnp->gp_seq));
+ 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;
+}
+
+/*
+ * 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)
+{
+ current->rcu_read_lock_nesting++;
+ 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 (t->rcu_read_lock_nesting != 1) {
+ --t->rcu_read_lock_nesting;
+ } else {
+ barrier(); /* critical section before exit code. */
+ t->rcu_read_lock_nesting = INT_MIN;
+ 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 */
+ t->rcu_read_lock_nesting = 0;
+ }
+#ifdef CONFIG_PROVE_LOCKING
+ {
+ int rrln = READ_ONCE(t->rcu_read_lock_nesting);
+
+ WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+ }
+#endif /* #ifdef CONFIG_PROVE_LOCKING */
+}
+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);
+}
+
+/*
+ * 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)
+{
+ 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);
+ 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_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->gp_seq, 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)) {
+ /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
+ drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
+ if (&t->rcu_node_entry == rnp->boost_tasks)
+ rnp->boost_tasks = np;
+ }
+
+ /*
+ * 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->gp_seq,
+ 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_futex_unlock(&rnp->boost_mtx);
+
+ /*
+ * If this was the last task on the expedited lists,
+ * then we need to report up the rcu_node hierarchy.
+ */
+ if (!empty_exp && empty_exp_now)
+ rcu_report_exp_rnp(rcu_state_p, rnp, true);
+ } else {
+ local_irq_restore(flags);
+ }
+}
+
+/*
+ * 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 task_struct *t;
+
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (!rcu_preempt_blocked_readers_cgp(rnp)) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ t = list_entry(rnp->gp_tasks->prev,
+ struct task_struct, rcu_node_entry);
+ list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+ /*
+ * We could be printing a lot while holding a spinlock.
+ * Avoid triggering hard lockup.
+ */
+ touch_nmi_watchdog();
+ sched_show_task(t);
+ }
+ raw_spin_unlock_irqrestore_rcu_node(rnp, 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);
+}
+
+static void rcu_print_task_stall_begin(struct rcu_node *rnp)
+{
+ pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
+ rnp->level, rnp->grplo, rnp->grphi);
+}
+
+static void rcu_print_task_stall_end(void)
+{
+ pr_cont("\n");
+}
+
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp)
+{
+ struct task_struct *t;
+ int ndetected = 0;
+
+ if (!rcu_preempt_blocked_readers_cgp(rnp))
+ return 0;
+ rcu_print_task_stall_begin(rnp);
+ t = list_entry(rnp->gp_tasks->prev,
+ struct task_struct, rcu_node_entry);
+ list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+ pr_cont(" P%d", t->pid);
+ ndetected++;
+ }
+ rcu_print_task_stall_end();
+ return ndetected;
+}
+
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each that is blocking the current
+ * expedited grace period.
+ */
+static int rcu_print_task_exp_stall(struct rcu_node *rnp)
+{
+ struct task_struct *t;
+ int ndetected = 0;
+
+ if (!rnp->exp_tasks)
+ return 0;
+ t = list_entry(rnp->exp_tasks->prev,
+ struct task_struct, rcu_node_entry);
+ list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+ pr_cont(" P%d", t->pid);
+ ndetected++;
+ }
+ return ndetected;
+}
+
+/*
+ * 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 ->gp_seq, and the rnp's ->lock
+ * must be held by the caller.
+ *
+ * Also, if there are blocked tasks on the list, they automatically
+ * block the newly created grace period, so set up ->gp_tasks accordingly.
+ */
+static void
+rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ struct task_struct *t;
+
+ RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
+ if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
+ dump_blkd_tasks(rsp, rnp, 10);
+ if (rcu_preempt_has_tasks(rnp) &&
+ (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
+ rnp->gp_tasks = rnp->blkd_tasks.next;
+ t = container_of(rnp->gp_tasks, struct task_struct,
+ rcu_node_entry);
+ trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
+ rnp->gp_seq, t->pid);
+ }
+ WARN_ON_ONCE(rnp->qsmask);
+}
+
+/*
+ * 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(void)
+{
+ struct rcu_state *rsp = &rcu_preempt_state;
+ struct task_struct *t = current;
+
+ if (t->rcu_read_lock_nesting == 0) {
+ rcu_preempt_qs();
+ return;
+ }
+ if (t->rcu_read_lock_nesting > 0 &&
+ __this_cpu_read(rcu_data_p->core_needs_qs) &&
+ __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm) &&
+ !t->rcu_read_unlock_special.b.need_qs &&
+ time_after(jiffies, rsp->gp_start + HZ))
+ t->rcu_read_unlock_special.b.need_qs = true;
+}
+
+/**
+ * call_rcu() - Queue an RCU callback for invocation after a grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed. However, the callback function
+ * might well execute concurrently with RCU read-side critical sections
+ * that started after call_rcu() was invoked. RCU read-side critical
+ * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
+ * and may be nested.
+ *
+ * Note that all CPUs must agree that the grace period extended beyond
+ * all pre-existing RCU read-side critical section. On systems with more
+ * than one CPU, this means that when "func()" is invoked, each CPU is
+ * guaranteed to have executed a full memory barrier since the end of its
+ * last RCU read-side critical section whose beginning preceded the call
+ * to call_rcu(). It also means that each CPU executing an RCU read-side
+ * critical section that continues beyond the start of "func()" must have
+ * executed a memory barrier after the call_rcu() but before the beginning
+ * of that RCU read-side critical section. Note that these guarantees
+ * include CPUs that are offline, idle, or executing in user mode, as
+ * well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
+ * resulting RCU callback function "func()", then both CPU A and CPU B are
+ * guaranteed to execute a full memory barrier during the time interval
+ * between the call to call_rcu() and the invocation of "func()" -- even
+ * if CPU A and CPU B are the same CPU (but again only if the system has
+ * more than one CPU).
+ */
+void call_rcu(struct rcu_head *head, rcu_callback_t func)
+{
+ __call_rcu(head, func, rcu_state_p, -1, 0);
+}
+EXPORT_SYMBOL_GPL(call_rcu);
+
+/**
+ * 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. Note, however, that
+ * upon return from synchronize_rcu(), the caller might well be executing
+ * concurrently with new RCU read-side critical sections that began while
+ * synchronize_rcu() was waiting. RCU read-side critical sections are
+ * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
+ *
+ * See the description of synchronize_sched() for more detailed
+ * information on memory-ordering guarantees. However, please note
+ * that -only- the memory-ordering guarantees apply. For example,
+ * synchronize_rcu() is -not- guaranteed to wait on things like code
+ * protected by preempt_disable(), instead, synchronize_rcu() is -only-
+ * guaranteed to wait on RCU read-side critical sections, that is, sections
+ * of code protected by rcu_read_lock().
+ */
+void synchronize_rcu(void)
+{
+ RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+ lock_is_held(&rcu_lock_map) ||
+ lock_is_held(&rcu_sched_lock_map),
+ "Illegal synchronize_rcu() in RCU read-side critical section");
+ if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+ return;
+ if (rcu_gp_is_expedited())
+ synchronize_rcu_expedited();
+ else
+ wait_rcu_gp(call_rcu);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu);
+
+/**
+ * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
+ *
+ * Note that this primitive does not necessarily wait for an RCU grace period
+ * to complete. For example, if there are no RCU callbacks queued anywhere
+ * in the system, then rcu_barrier() is within its rights to return
+ * immediately, without waiting for anything, much less an RCU grace period.
+ */
+void rcu_barrier(void)
+{
+ _rcu_barrier(rcu_state_p);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier);
+
+/*
+ * Initialize preemptible RCU's state structures.
+ */
+static void __init __rcu_init_preempt(void)
+{
+ rcu_init_one(rcu_state_p);
+}
+
+/*
+ * Check for a task exiting while in a preemptible-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 (likely(list_empty(¤t->rcu_node_entry)))
+ return;
+ t->rcu_read_lock_nesting = 1;
+ barrier();
+ t->rcu_read_unlock_special.b.blocked = true;
+ __rcu_read_unlock();
+}
+
+/*
+ * Dump the blocked-tasks state, but limit the list dump to the
+ * specified number of elements.
+ */
+static void
+dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)
+{
+ int cpu;
+ int i;
+ struct list_head *lhp;
+ bool onl;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp1;
+
+ raw_lockdep_assert_held_rcu_node(rnp);
+ pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
+ __func__, rnp->grplo, rnp->grphi, rnp->level,
+ (long)rnp->gp_seq, (long)rnp->completedqs);
+ for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
+ pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
+ __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
+ pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
+ __func__, rnp->gp_tasks, rnp->boost_tasks, rnp->exp_tasks);
+ pr_info("%s: ->blkd_tasks", __func__);
+ i = 0;
+ list_for_each(lhp, &rnp->blkd_tasks) {
+ pr_cont(" %p", lhp);
+ if (++i >= 10)
+ break;
+ }
+ pr_cont("\n");
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
+ rdp = per_cpu_ptr(rsp->rda, cpu);
+ onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
+ pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
+ cpu, ".o"[onl],
+ (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
+ (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
+ }
+}
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+static struct rcu_state *const rcu_state_p = &rcu_sched_state;
+
+/*
+ * Tell them what RCU they are running.
+ */
+static void __init rcu_bootup_announce(void)
+{
+ pr_info("Hierarchical RCU implementation.\n");
+ rcu_bootup_announce_oddness();
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * CPUs being in quiescent states.
+ */
+static void rcu_preempt_note_context_switch(bool preempt)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, there are never any preempted
+ * RCU readers.
+ */
+static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
+{
+ return 0;
+}
+
+/*
+ * Because there is no preemptible RCU, there can be no readers blocked.
+ */
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
+{
+ return false;
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp)
+{
+ return 0;
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections that are
+ * blocking the current expedited grace period.
+ */
+static int rcu_print_task_exp_stall(struct rcu_node *rnp)
+{
+ return 0;
+}
+
+/*
+ * Because there is no preemptible RCU, there can be no readers blocked,
+ * so there is no need to check for blocked tasks. So check only for
+ * bogus qsmask values.
+ */
+static void
+rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ WARN_ON_ONCE(rnp->qsmask);
+}
+
+/*
+ * Because preemptible RCU does not exist, it never has any callbacks
+ * to check.
+ */
+static void rcu_preempt_check_callbacks(void)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, rcu_barrier() is just
+ * another name for rcu_barrier_sched().
+ */
+void rcu_barrier(void)
+{
+ rcu_barrier_sched();
+}
+EXPORT_SYMBOL_GPL(rcu_barrier);
+
+/*
+ * Because preemptible RCU does not exist, it need not be initialized.
+ */
+static void __init __rcu_init_preempt(void)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, tasks cannot possibly exit
+ * while in preemptible RCU read-side critical sections.
+ */
+void exit_rcu(void)
+{
+}
+
+/*
+ * Dump the guaranteed-empty blocked-tasks state. Trust but verify.
+ */
+static void
+dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)
+{
+ WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
+}
+
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
+#ifdef CONFIG_RCU_BOOST
+
+static void rcu_wake_cond(struct task_struct *t, int status)
+{
+ /*
+ * If the thread is yielding, only wake it when this
+ * is invoked from idle
+ */
+ if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
+ wake_up_process(t);
+}
+
+/*
+ * Carry out RCU priority boosting on the task indicated by ->exp_tasks
+ * or ->boost_tasks, advancing the pointer to the next task in the
+ * ->blkd_tasks list.
+ *
+ * Note that irqs must be enabled: boosting the task can block.
+ * Returns 1 if there are more tasks needing to be boosted.
+ */
+static int rcu_boost(struct rcu_node *rnp)
+{
+ unsigned long flags;
+ struct task_struct *t;
+ struct list_head *tb;
+
+ if (READ_ONCE(rnp->exp_tasks) == NULL &&
+ READ_ONCE(rnp->boost_tasks) == NULL)
+ return 0; /* Nothing left to boost. */
+
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+
+ /*
+ * Recheck under the lock: all tasks in need of boosting
+ * might exit their RCU read-side critical sections on their own.
+ */
+ if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return 0;
+ }
+
+ /*
+ * Preferentially boost tasks blocking expedited grace periods.
+ * This cannot starve the normal grace periods because a second
+ * expedited grace period must boost all blocked tasks, including
+ * those blocking the pre-existing normal grace period.
+ */
+ if (rnp->exp_tasks != NULL)
+ tb = rnp->exp_tasks;
+ else
+ tb = rnp->boost_tasks;
+
+ /*
+ * We boost task t by manufacturing an rt_mutex that appears to
+ * be held by task t. We leave a pointer to that rt_mutex where
+ * task t can find it, and task t will release the mutex when it
+ * exits its outermost RCU read-side critical section. Then
+ * simply acquiring this artificial rt_mutex will boost task
+ * t's priority. (Thanks to tglx for suggesting this approach!)
+ *
+ * Note that task t must acquire rnp->lock to remove itself from
+ * the ->blkd_tasks list, which it will do from exit() if from
+ * nowhere else. We therefore are guaranteed that task t will
+ * stay around at least until we drop rnp->lock. Note that
+ * rnp->lock also resolves races between our priority boosting
+ * and task t's exiting its outermost RCU read-side critical
+ * section.
+ */
+ t = container_of(tb, struct task_struct, rcu_node_entry);
+ rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ /* Lock only for side effect: boosts task t's priority. */
+ rt_mutex_lock(&rnp->boost_mtx);
+ rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
+
+ return READ_ONCE(rnp->exp_tasks) != NULL ||
+ READ_ONCE(rnp->boost_tasks) != NULL;
+}
+
+/*
+ * Priority-boosting kthread, one per leaf rcu_node.
+ */
+static int rcu_boost_kthread(void *arg)
+{
+ struct rcu_node *rnp = (struct rcu_node *)arg;
+ int spincnt = 0;
+ int more2boost;
+
+ trace_rcu_utilization(TPS("Start boost kthread@init"));
+ for (;;) {
+ rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
+ trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
+ rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
+ trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
+ rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
+ more2boost = rcu_boost(rnp);
+ if (more2boost)
+ spincnt++;
+ else
+ spincnt = 0;
+ if (spincnt > 10) {
+ rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
+ trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
+ schedule_timeout_interruptible(2);
+ trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
+ spincnt = 0;
+ }
+ }
+ /* NOTREACHED */
+ trace_rcu_utilization(TPS("End boost kthread@notreached"));
+ return 0;
+}
+
+/*
+ * Check to see if it is time to start boosting RCU readers that are
+ * blocking the current grace period, and, if so, tell the per-rcu_node
+ * kthread to start boosting them. If there is an expedited grace
+ * period in progress, it is always time to boost.
+ *
+ * The caller must hold rnp->lock, which this function releases.
+ * The ->boost_kthread_task is immortal, so we don't need to worry
+ * about it going away.
+ */
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
+ __releases(rnp->lock)
+{
+ struct task_struct *t;
+
+ raw_lockdep_assert_held_rcu_node(rnp);
+ if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ if (rnp->exp_tasks != NULL ||
+ (rnp->gp_tasks != NULL &&
+ rnp->boost_tasks == NULL &&
+ rnp->qsmask == 0 &&
+ ULONG_CMP_GE(jiffies, rnp->boost_time))) {
+ if (rnp->exp_tasks == NULL)
+ rnp->boost_tasks = rnp->gp_tasks;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ t = rnp->boost_kthread_task;
+ if (t)
+ rcu_wake_cond(t, rnp->boost_kthread_status);
+ } else {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ }
+}
+
+/*
+ * Wake up the per-CPU kthread to invoke RCU callbacks.
+ */
+static void invoke_rcu_callbacks_kthread(void)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ __this_cpu_write(rcu_cpu_has_work, 1);
+ if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
+ current != __this_cpu_read(rcu_cpu_kthread_task)) {
+ rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
+ __this_cpu_read(rcu_cpu_kthread_status));
+ }
+ local_irq_restore(flags);
+}
+
+/*
+ * Is the current CPU running the RCU-callbacks kthread?
+ * Caller must have preemption disabled.
+ */
+static bool rcu_is_callbacks_kthread(void)
+{
+ return __this_cpu_read(rcu_cpu_kthread_task) == current;
+}
+
+#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
+
+/*
+ * Do priority-boost accounting for the start of a new grace period.
+ */
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
+{
+ rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
+}
+
+/*
+ * Create an RCU-boost kthread for the specified node if one does not
+ * already exist. We only create this kthread for preemptible RCU.
+ * Returns zero if all is well, a negated errno otherwise.
+ */
+static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
+ struct rcu_node *rnp)
+{
+ int rnp_index = rnp - &rsp->node[0];
+ unsigned long flags;
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (rcu_state_p != rsp)
+ return 0;
+
+ if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
+ return 0;
+
+ rsp->boost = 1;
+ if (rnp->boost_kthread_task != NULL)
+ return 0;
+ t = kthread_create(rcu_boost_kthread, (void *)rnp,
+ "rcub/%d", rnp_index);
+ if (IS_ERR(t))
+ return PTR_ERR(t);
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ rnp->boost_kthread_task = t;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ sp.sched_priority = kthread_prio;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
+ return 0;
+}
+
+static void rcu_kthread_do_work(void)
+{
+ rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
+ rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
+ rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
+}
+
+static void rcu_cpu_kthread_setup(unsigned int cpu)
+{
+ struct sched_param sp;
+
+ sp.sched_priority = kthread_prio;
+ sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+}
+
+static void rcu_cpu_kthread_park(unsigned int cpu)
+{
+ per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+}
+
+static int rcu_cpu_kthread_should_run(unsigned int cpu)
+{
+ return __this_cpu_read(rcu_cpu_has_work);
+}
+
+/*
+ * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
+ * RCU softirq used in flavors and configurations of RCU that do not
+ * support RCU priority boosting.
+ */
+static void rcu_cpu_kthread(unsigned int cpu)
+{
+ unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
+ char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
+ int spincnt;
+
+ for (spincnt = 0; spincnt < 10; spincnt++) {
+ trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
+ local_bh_disable();
+ *statusp = RCU_KTHREAD_RUNNING;
+ this_cpu_inc(rcu_cpu_kthread_loops);
+ local_irq_disable();
+ work = *workp;
+ *workp = 0;
+ local_irq_enable();
+ if (work)
+ rcu_kthread_do_work();
+ local_bh_enable();
+ if (*workp == 0) {
+ trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
+ *statusp = RCU_KTHREAD_WAITING;
+ return;
+ }
+ }
+ *statusp = RCU_KTHREAD_YIELDING;
+ trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
+ schedule_timeout_interruptible(2);
+ trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
+ *statusp = RCU_KTHREAD_WAITING;
+}
+
+/*
+ * Set the per-rcu_node kthread's affinity to cover all CPUs that are
+ * served by the rcu_node in question. The CPU hotplug lock is still
+ * held, so the value of rnp->qsmaskinit will be stable.
+ *
+ * We don't include outgoingcpu in the affinity set, use -1 if there is
+ * no outgoing CPU. If there are no CPUs left in the affinity set,
+ * this function allows the kthread to execute on any CPU.
+ */
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+ struct task_struct *t = rnp->boost_kthread_task;
+ unsigned long mask = rcu_rnp_online_cpus(rnp);
+ cpumask_var_t cm;
+ int cpu;
+
+ if (!t)
+ return;
+ if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
+ return;
+ for_each_leaf_node_possible_cpu(rnp, cpu)
+ if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
+ cpu != outgoingcpu)
+ cpumask_set_cpu(cpu, cm);
+ if (cpumask_weight(cm) == 0)
+ cpumask_setall(cm);
+ set_cpus_allowed_ptr(t, cm);
+ free_cpumask_var(cm);
+}
+
+static struct smp_hotplug_thread rcu_cpu_thread_spec = {
+ .store = &rcu_cpu_kthread_task,
+ .thread_should_run = rcu_cpu_kthread_should_run,
+ .thread_fn = rcu_cpu_kthread,
+ .thread_comm = "rcuc/%u",
+ .setup = rcu_cpu_kthread_setup,
+ .park = rcu_cpu_kthread_park,
+};
+
+/*
+ * Spawn boost kthreads -- called as soon as the scheduler is running.
+ */
+static void __init rcu_spawn_boost_kthreads(void)
+{
+ struct rcu_node *rnp;
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ per_cpu(rcu_cpu_has_work, cpu) = 0;
+ BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
+ rcu_for_each_leaf_node(rcu_state_p, rnp)
+ (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
+}
+
+static void rcu_prepare_kthreads(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
+ struct rcu_node *rnp = rdp->mynode;
+
+ /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
+ if (rcu_scheduler_fully_active)
+ (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
+}
+
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
+ __releases(rnp->lock)
+{
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+}
+
+static void invoke_rcu_callbacks_kthread(void)
+{
+ WARN_ON_ONCE(1);
+}
+
+static bool rcu_is_callbacks_kthread(void)
+{
+ return false;
+}
+
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
+{
+}
+
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+}
+
+static void __init rcu_spawn_boost_kthreads(void)
+{
+}
+
+static void rcu_prepare_kthreads(int cpu)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
+#if !defined(CONFIG_RCU_FAST_NO_HZ)
+
+/*
+ * Check to see if any future RCU-related work will need to be done
+ * by the current CPU, even if none need be done immediately, returning
+ * 1 if so. This function is part of the RCU implementation; it is -not-
+ * an exported member of the RCU API.
+ *
+ * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
+ * any flavor of RCU.
+ */
+int rcu_needs_cpu(u64 basemono, u64 *nextevt)
+{
+ *nextevt = KTIME_MAX;
+ return rcu_cpu_has_callbacks(NULL);
+}
+
+/*
+ * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
+ * after it.
+ */
+static void rcu_cleanup_after_idle(void)
+{
+}
+
+/*
+ * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
+ * is nothing.
+ */
+static void rcu_prepare_for_idle(void)
+{
+}
+
+/*
+ * Don't bother keeping a running count of the number of RCU callbacks
+ * posted because CONFIG_RCU_FAST_NO_HZ=n.
+ */
+static void rcu_idle_count_callbacks_posted(void)
+{
+}
+
+#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
+
+/*
+ * This code is invoked when a CPU goes idle, at which point we want
+ * to have the CPU do everything required for RCU so that it can enter
+ * the energy-efficient dyntick-idle mode. This is handled by a
+ * state machine implemented by rcu_prepare_for_idle() below.
+ *
+ * The following three proprocessor symbols control this state machine:
+ *
+ * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
+ * to sleep in dyntick-idle mode with RCU callbacks pending. This
+ * is sized to be roughly one RCU grace period. Those energy-efficiency
+ * benchmarkers who might otherwise be tempted to set this to a large
+ * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
+ * system. And if you are -that- concerned about energy efficiency,
+ * just power the system down and be done with it!
+ * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
+ * permitted to sleep in dyntick-idle mode with only lazy RCU
+ * callbacks pending. Setting this too high can OOM your system.
+ *
+ * The values below work well in practice. If future workloads require
+ * adjustment, they can be converted into kernel config parameters, though
+ * making the state machine smarter might be a better option.
+ */
+#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
+#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
+
+static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
+module_param(rcu_idle_gp_delay, int, 0644);
+static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
+module_param(rcu_idle_lazy_gp_delay, int, 0644);
+
+/*
+ * Try to advance callbacks for all flavors of RCU on the current CPU, but
+ * only if it has been awhile since the last time we did so. Afterwards,
+ * if there are any callbacks ready for immediate invocation, return true.
+ */
+static bool __maybe_unused rcu_try_advance_all_cbs(void)
+{
+ bool cbs_ready = false;
+ struct rcu_data *rdp;
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ struct rcu_node *rnp;
+ struct rcu_state *rsp;
+
+ /* Exit early if we advanced recently. */
+ if (jiffies == rdtp->last_advance_all)
+ return false;
+ rdtp->last_advance_all = jiffies;
+
+ for_each_rcu_flavor(rsp) {
+ rdp = this_cpu_ptr(rsp->rda);
+ rnp = rdp->mynode;
+
+ /*
+ * Don't bother checking unless a grace period has
+ * completed since we last checked and there are
+ * callbacks not yet ready to invoke.
+ */
+ if ((rcu_seq_completed_gp(rdp->gp_seq,
+ rcu_seq_current(&rnp->gp_seq)) ||
+ unlikely(READ_ONCE(rdp->gpwrap))) &&
+ rcu_segcblist_pend_cbs(&rdp->cblist))
+ note_gp_changes(rsp, rdp);
+
+ if (rcu_segcblist_ready_cbs(&rdp->cblist))
+ cbs_ready = true;
+ }
+ return cbs_ready;
+}
+
+/*
+ * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
+ * to invoke. If the CPU has callbacks, try to advance them. Tell the
+ * caller to set the timeout based on whether or not there are non-lazy
+ * callbacks.
+ *
+ * The caller must have disabled interrupts.
+ */
+int rcu_needs_cpu(u64 basemono, u64 *nextevt)
+{
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ unsigned long dj;
+
+ lockdep_assert_irqs_disabled();
+
+ /* Snapshot to detect later posting of non-lazy callback. */
+ rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
+
+ /* If no callbacks, RCU doesn't need the CPU. */
+ if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
+ *nextevt = KTIME_MAX;
+ return 0;
+ }
+
+ /* Attempt to advance callbacks. */
+ if (rcu_try_advance_all_cbs()) {
+ /* Some ready to invoke, so initiate later invocation. */
+ invoke_rcu_core();
+ return 1;
+ }
+ rdtp->last_accelerate = jiffies;
+
+ /* Request timer delay depending on laziness, and round. */
+ if (!rdtp->all_lazy) {
+ dj = round_up(rcu_idle_gp_delay + jiffies,
+ rcu_idle_gp_delay) - jiffies;
+ } else {
+ dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
+ }
+ *nextevt = basemono + dj * TICK_NSEC;
+ return 0;
+}
+
+/*
+ * Prepare a CPU for idle from an RCU perspective. The first major task
+ * is to sense whether nohz mode has been enabled or disabled via sysfs.
+ * The second major task is to check to see if a non-lazy callback has
+ * arrived at a CPU that previously had only lazy callbacks. The third
+ * major task is to accelerate (that is, assign grace-period numbers to)
+ * any recently arrived callbacks.
+ *
+ * The caller must have disabled interrupts.
+ */
+static void rcu_prepare_for_idle(void)
+{
+ bool needwake;
+ struct rcu_data *rdp;
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ struct rcu_node *rnp;
+ struct rcu_state *rsp;
+ int tne;
+
+ lockdep_assert_irqs_disabled();
+ if (rcu_is_nocb_cpu(smp_processor_id()))
+ return;
+
+ /* Handle nohz enablement switches conservatively. */
+ tne = READ_ONCE(tick_nohz_active);
+ if (tne != rdtp->tick_nohz_enabled_snap) {
+ if (rcu_cpu_has_callbacks(NULL))
+ invoke_rcu_core(); /* force nohz to see update. */
+ rdtp->tick_nohz_enabled_snap = tne;
+ return;
+ }
+ if (!tne)
+ return;
+
+ /*
+ * If a non-lazy callback arrived at a CPU having only lazy
+ * callbacks, invoke RCU core for the side-effect of recalculating
+ * idle duration on re-entry to idle.
+ */
+ if (rdtp->all_lazy &&
+ rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
+ rdtp->all_lazy = false;
+ rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
+ invoke_rcu_core();
+ return;
+ }
+
+ /*
+ * If we have not yet accelerated this jiffy, accelerate all
+ * callbacks on this CPU.
+ */
+ if (rdtp->last_accelerate == jiffies)
+ return;
+ rdtp->last_accelerate = jiffies;
+ for_each_rcu_flavor(rsp) {
+ rdp = this_cpu_ptr(rsp->rda);
+ if (!rcu_segcblist_pend_cbs(&rdp->cblist))
+ continue;
+ rnp = rdp->mynode;
+ raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+ needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
+ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+ if (needwake)
+ rcu_gp_kthread_wake(rsp);
+ }
+}
+
+/*
+ * Clean up for exit from idle. Attempt to advance callbacks based on
+ * any grace periods that elapsed while the CPU was idle, and if any
+ * callbacks are now ready to invoke, initiate invocation.
+ */
+static void rcu_cleanup_after_idle(void)
+{
+ lockdep_assert_irqs_disabled();
+ if (rcu_is_nocb_cpu(smp_processor_id()))
+ return;
+ if (rcu_try_advance_all_cbs())
+ invoke_rcu_core();
+}
+
+/*
+ * Keep a running count of the number of non-lazy callbacks posted
+ * on this CPU. This running counter (which is never decremented) allows
+ * rcu_prepare_for_idle() to detect when something out of the idle loop
+ * posts a callback, even if an equal number of callbacks are invoked.
+ * Of course, callbacks should only be posted from within a trace event
+ * designed to be called from idle or from within RCU_NONIDLE().
+ */
+static void rcu_idle_count_callbacks_posted(void)
+{
+ __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
+}
+
+/*
+ * Data for flushing lazy RCU callbacks at OOM time.
+ */
+static atomic_t oom_callback_count;
+static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
+
+/*
+ * RCU OOM callback -- decrement the outstanding count and deliver the
+ * wake-up if we are the last one.
+ */
+static void rcu_oom_callback(struct rcu_head *rhp)
+{
+ if (atomic_dec_and_test(&oom_callback_count))
+ wake_up(&oom_callback_wq);
+}
+
+/*
+ * Post an rcu_oom_notify callback on the current CPU if it has at
+ * least one lazy callback. This will unnecessarily post callbacks
+ * to CPUs that already have a non-lazy callback at the end of their
+ * callback list, but this is an infrequent operation, so accept some
+ * extra overhead to keep things simple.
+ */
+static void rcu_oom_notify_cpu(void *unused)
+{
+ struct rcu_state *rsp;
+ struct rcu_data *rdp;
+
+ for_each_rcu_flavor(rsp) {
+ rdp = raw_cpu_ptr(rsp->rda);
+ if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
+ atomic_inc(&oom_callback_count);
+ rsp->call(&rdp->oom_head, rcu_oom_callback);
+ }
+ }
+}
+
+/*
+ * If low on memory, ensure that each CPU has a non-lazy callback.
+ * This will wake up CPUs that have only lazy callbacks, in turn
+ * ensuring that they free up the corresponding memory in a timely manner.
+ * Because an uncertain amount of memory will be freed in some uncertain
+ * timeframe, we do not claim to have freed anything.
+ */
+static int rcu_oom_notify(struct notifier_block *self,
+ unsigned long notused, void *nfreed)
+{
+ int cpu;
+
+ /* Wait for callbacks from earlier instance to complete. */
+ wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
+ smp_mb(); /* Ensure callback reuse happens after callback invocation. */
+
+ /*
+ * Prevent premature wakeup: ensure that all increments happen
+ * before there is a chance of the counter reaching zero.
+ */
+ atomic_set(&oom_callback_count, 1);
+
+ for_each_online_cpu(cpu) {
+ smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
+ cond_resched_tasks_rcu_qs();
+ }
+
+ /* Unconditionally decrement: no need to wake ourselves up. */
+ atomic_dec(&oom_callback_count);
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block rcu_oom_nb = {
+ .notifier_call = rcu_oom_notify
+};
+
+static int __init rcu_register_oom_notifier(void)
+{
+ register_oom_notifier(&rcu_oom_nb);
+ return 0;
+}
+early_initcall(rcu_register_oom_notifier);
+
+#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
+
+#ifdef CONFIG_RCU_FAST_NO_HZ
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+ struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+ unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
+
+ sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
+ rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
+ ulong2long(nlpd),
+ rdtp->all_lazy ? 'L' : '.',
+ rdtp->tick_nohz_enabled_snap ? '.' : 'D');
+}
+
+#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+ *cp = '\0';
+}
+
+#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+/* Initiate the stall-info list. */
+static void print_cpu_stall_info_begin(void)
+{
+ pr_cont("\n");
+}
+
+/*
+ * Print out diagnostic information for the specified stalled CPU.
+ *
+ * If the specified CPU is aware of the current RCU grace period
+ * (flavor specified by rsp), then print the number of scheduling
+ * clock interrupts the CPU has taken during the time that it has
+ * been aware. Otherwise, print the number of RCU grace periods
+ * that this CPU is ignorant of, for example, "1" if the CPU was
+ * aware of the previous grace period.
+ *
+ * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
+ */
+static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
+{
+ unsigned long delta;
+ char fast_no_hz[72];
+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+ struct rcu_dynticks *rdtp = rdp->dynticks;
+ char *ticks_title;
+ unsigned long ticks_value;
+
+ /*
+ * We could be printing a lot while holding a spinlock. Avoid
+ * triggering hard lockup.
+ */
+ touch_nmi_watchdog();
+
+ ticks_value = rcu_seq_ctr(rsp->gp_seq - rdp->gp_seq);
+ if (ticks_value) {
+ ticks_title = "GPs behind";
+ } else {
+ ticks_title = "ticks this GP";
+ ticks_value = rdp->ticks_this_gp;
+ }
+ print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
+ delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
+ pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
+ cpu,
+ "O."[!!cpu_online(cpu)],
+ "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
+ "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
+ !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
+ rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
+ "!."[!delta],
+ ticks_value, ticks_title,
+ rcu_dynticks_snap(rdtp) & 0xfff,
+ rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
+ rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
+ READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
+ fast_no_hz);
+}
+
+/* Terminate the stall-info list. */
+static void print_cpu_stall_info_end(void)
+{
+ pr_err("\t");
+}
+
+/* Zero ->ticks_this_gp for all flavors of RCU. */
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+ rdp->ticks_this_gp = 0;
+ rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
+}
+
+/* Increment ->ticks_this_gp for all flavors of RCU. */
+static void increment_cpu_stall_ticks(void)
+{
+ struct rcu_state *rsp;
+
+ for_each_rcu_flavor(rsp)
+ raw_cpu_inc(rsp->rda->ticks_this_gp);
+}
+
+#ifdef CONFIG_RCU_NOCB_CPU
+
+/*
+ * Offload callback processing from the boot-time-specified set of CPUs
+ * specified by rcu_nocb_mask. For each CPU in the set, there is a
+ * kthread created that pulls the callbacks from the corresponding CPU,
+ * waits for a grace period to elapse, and invokes the callbacks.
+ * The no-CBs CPUs do a wake_up() on their kthread when they insert
+ * a callback into any empty list, unless the rcu_nocb_poll boot parameter
+ * has been specified, in which case each kthread actively polls its
+ * CPU. (Which isn't so great for energy efficiency, but which does
+ * reduce RCU's overhead on that CPU.)
+ *
+ * This is intended to be used in conjunction with Frederic Weisbecker's
+ * adaptive-idle work, which would seriously reduce OS jitter on CPUs
+ * running CPU-bound user-mode computations.
+ *
+ * Offloading of callback processing could also in theory be used as
+ * an energy-efficiency measure because CPUs with no RCU callbacks
+ * queued are more aggressive about entering dyntick-idle mode.
+ */
+
+
+/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
+static int __init rcu_nocb_setup(char *str)
+{
+ alloc_bootmem_cpumask_var(&rcu_nocb_mask);
+ cpulist_parse(str, rcu_nocb_mask);
+ return 1;
+}
+__setup("rcu_nocbs=", rcu_nocb_setup);
+
+static int __init parse_rcu_nocb_poll(char *arg)
+{
+ rcu_nocb_poll = true;
+ return 0;
+}
+early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
+
+/*
+ * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
+ * grace period.
+ */
+static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
+{
+ swake_up_all(sq);
+}
+
+static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
+{
+ return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
+}
+
+static void rcu_init_one_nocb(struct rcu_node *rnp)
+{
+ init_swait_queue_head(&rnp->nocb_gp_wq[0]);
+ init_swait_queue_head(&rnp->nocb_gp_wq[1]);
+}
+
+/* Is the specified CPU a no-CBs CPU? */
+bool rcu_is_nocb_cpu(int cpu)
+{
+ if (cpumask_available(rcu_nocb_mask))
+ return cpumask_test_cpu(cpu, rcu_nocb_mask);
+ return false;
+}
+
+/*
+ * Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock
+ * and this function releases it.
+ */
+static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
+ unsigned long flags)
+ __releases(rdp->nocb_lock)
+{
+ struct rcu_data *rdp_leader = rdp->nocb_leader;
+
+ lockdep_assert_held(&rdp->nocb_lock);
+ if (!READ_ONCE(rdp_leader->nocb_kthread)) {
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ return;
+ }
+ if (rdp_leader->nocb_leader_sleep || force) {
+ /* Prior smp_mb__after_atomic() orders against prior enqueue. */
+ WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
+ del_timer(&rdp->nocb_timer);
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ smp_mb(); /* ->nocb_leader_sleep before swake_up_one(). */
+ swake_up_one(&rdp_leader->nocb_wq);
+ } else {
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ }
+}
+
+/*
+ * Kick the leader kthread for this NOCB group, but caller has not
+ * acquired locks.
+ */
+static void wake_nocb_leader(struct rcu_data *rdp, bool force)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+ __wake_nocb_leader(rdp, force, flags);
+}
+
+/*
+ * Arrange to wake the leader kthread for this NOCB group at some
+ * future time when it is safe to do so.
+ */
+static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
+ const char *reason)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+ if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
+ mod_timer(&rdp->nocb_timer, jiffies + 1);
+ WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, reason);
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+}
+
+/*
+ * Does the specified CPU need an RCU callback for the specified flavor
+ * of rcu_barrier()?
+ */
+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+ unsigned long ret;
+#ifdef CONFIG_PROVE_RCU
+ struct rcu_head *rhp;
+#endif /* #ifdef CONFIG_PROVE_RCU */
+
+ /*
+ * Check count of all no-CBs callbacks awaiting invocation.
+ * There needs to be a barrier before this function is called,
+ * but associated with a prior determination that no more
+ * callbacks would be posted. In the worst case, the first
+ * barrier in _rcu_barrier() suffices (but the caller cannot
+ * necessarily rely on this, not a substitute for the caller
+ * getting the concurrency design right!). There must also be
+ * a barrier between the following load an posting of a callback
+ * (if a callback is in fact needed). This is associated with an
+ * atomic_inc() in the caller.
+ */
+ ret = atomic_long_read(&rdp->nocb_q_count);
+
+#ifdef CONFIG_PROVE_RCU
+ rhp = READ_ONCE(rdp->nocb_head);
+ if (!rhp)
+ rhp = READ_ONCE(rdp->nocb_gp_head);
+ if (!rhp)
+ rhp = READ_ONCE(rdp->nocb_follower_head);
+
+ /* Having no rcuo kthread but CBs after scheduler starts is bad! */
+ if (!READ_ONCE(rdp->nocb_kthread) && rhp &&
+ rcu_scheduler_fully_active) {
+ /* RCU callback enqueued before CPU first came online??? */
+ pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
+ cpu, rhp->func);
+ WARN_ON_ONCE(1);
+ }
+#endif /* #ifdef CONFIG_PROVE_RCU */
+
+ return !!ret;
+}
+
+/*
+ * Enqueue the specified string of rcu_head structures onto the specified
+ * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
+ * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
+ * counts are supplied by rhcount and rhcount_lazy.
+ *
+ * If warranted, also wake up the kthread servicing this CPUs queues.
+ */
+static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
+ struct rcu_head *rhp,
+ struct rcu_head **rhtp,
+ int rhcount, int rhcount_lazy,
+ unsigned long flags)
+{
+ int len;
+ struct rcu_head **old_rhpp;
+ struct task_struct *t;
+
+ /* Enqueue the callback on the nocb list and update counts. */
+ atomic_long_add(rhcount, &rdp->nocb_q_count);
+ /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
+ old_rhpp = xchg(&rdp->nocb_tail, rhtp);
+ WRITE_ONCE(*old_rhpp, rhp);
+ atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
+ smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
+
+ /* If we are not being polled and there is a kthread, awaken it ... */
+ t = READ_ONCE(rdp->nocb_kthread);
+ if (rcu_nocb_poll || !t) {
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WakeNotPoll"));
+ return;
+ }
+ len = atomic_long_read(&rdp->nocb_q_count);
+ if (old_rhpp == &rdp->nocb_head) {
+ if (!irqs_disabled_flags(flags)) {
+ /* ... if queue was empty ... */
+ wake_nocb_leader(rdp, false);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WakeEmpty"));
+ } else {
+ wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
+ TPS("WakeEmptyIsDeferred"));
+ }
+ rdp->qlen_last_fqs_check = 0;
+ } else if (len > rdp->qlen_last_fqs_check + qhimark) {
+ /* ... or if many callbacks queued. */
+ if (!irqs_disabled_flags(flags)) {
+ wake_nocb_leader(rdp, true);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WakeOvf"));
+ } else {
+ wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE_FORCE,
+ TPS("WakeOvfIsDeferred"));
+ }
+ rdp->qlen_last_fqs_check = LONG_MAX / 2;
+ } else {
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
+ }
+ return;
+}
+
+/*
+ * This is a helper for __call_rcu(), which invokes this when the normal
+ * callback queue is inoperable. If this is not a no-CBs CPU, this
+ * function returns failure back to __call_rcu(), which can complain
+ * appropriately.
+ *
+ * Otherwise, this function queues the callback where the corresponding
+ * "rcuo" kthread can find it.
+ */
+static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
+ bool lazy, unsigned long flags)
+{
+
+ if (!rcu_is_nocb_cpu(rdp->cpu))
+ return false;
+ __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
+ if (__is_kfree_rcu_offset((unsigned long)rhp->func))
+ trace_rcu_kfree_callback(rdp->rsp->name, rhp,
+ (unsigned long)rhp->func,
+ -atomic_long_read(&rdp->nocb_q_count_lazy),
+ -atomic_long_read(&rdp->nocb_q_count));
+ else
+ trace_rcu_callback(rdp->rsp->name, rhp,
+ -atomic_long_read(&rdp->nocb_q_count_lazy),
+ -atomic_long_read(&rdp->nocb_q_count));
+
+ /*
+ * If called from an extended quiescent state with interrupts
+ * disabled, invoke the RCU core in order to allow the idle-entry
+ * deferred-wakeup check to function.
+ */
+ if (irqs_disabled_flags(flags) &&
+ !rcu_is_watching() &&
+ cpu_online(smp_processor_id()))
+ invoke_rcu_core();
+
+ return true;
+}
+
+/*
+ * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
+ * not a no-CBs CPU.
+ */
+static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
+ struct rcu_data *rdp,
+ unsigned long flags)
+{
+ lockdep_assert_irqs_disabled();
+ if (!rcu_is_nocb_cpu(smp_processor_id()))
+ return false; /* Not NOCBs CPU, caller must migrate CBs. */
+ __call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist),
+ rcu_segcblist_tail(&rdp->cblist),
+ rcu_segcblist_n_cbs(&rdp->cblist),
+ rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags);
+ rcu_segcblist_init(&rdp->cblist);
+ rcu_segcblist_disable(&rdp->cblist);
+ return true;
+}
+
+/*
+ * If necessary, kick off a new grace period, and either way wait
+ * for a subsequent grace period to complete.
+ */
+static void rcu_nocb_wait_gp(struct rcu_data *rdp)
+{
+ unsigned long c;
+ bool d;
+ unsigned long flags;
+ bool needwake;
+ struct rcu_node *rnp = rdp->mynode;
+
+ local_irq_save(flags);
+ c = rcu_seq_snap(&rdp->rsp->gp_seq);
+ if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
+ local_irq_restore(flags);
+ } else {
+ raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+ needwake = rcu_start_this_gp(rnp, rdp, c);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ if (needwake)
+ rcu_gp_kthread_wake(rdp->rsp);
+ }
+
+ /*
+ * Wait for the grace period. Do so interruptibly to avoid messing
+ * up the load average.
+ */
+ trace_rcu_this_gp(rnp, rdp, c, TPS("StartWait"));
+ for (;;) {
+ swait_event_interruptible_exclusive(
+ rnp->nocb_gp_wq[rcu_seq_ctr(c) & 0x1],
+ (d = rcu_seq_done(&rnp->gp_seq, c)));
+ if (likely(d))
+ break;
+ WARN_ON(signal_pending(current));
+ trace_rcu_this_gp(rnp, rdp, c, TPS("ResumeWait"));
+ }
+ trace_rcu_this_gp(rnp, rdp, c, TPS("EndWait"));
+ smp_mb(); /* Ensure that CB invocation happens after GP end. */
+}
+
+/*
+ * Leaders come here to wait for additional callbacks to show up.
+ * This function does not return until callbacks appear.
+ */
+static void nocb_leader_wait(struct rcu_data *my_rdp)
+{
+ bool firsttime = true;
+ unsigned long flags;
+ bool gotcbs;
+ struct rcu_data *rdp;
+ struct rcu_head **tail;
+
+wait_again:
+
+ /* Wait for callbacks to appear. */
+ if (!rcu_nocb_poll) {
+ trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Sleep"));
+ swait_event_interruptible_exclusive(my_rdp->nocb_wq,
+ !READ_ONCE(my_rdp->nocb_leader_sleep));
+ raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
+ my_rdp->nocb_leader_sleep = true;
+ WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
+ del_timer(&my_rdp->nocb_timer);
+ raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
+ } else if (firsttime) {
+ firsttime = false; /* Don't drown trace log with "Poll"! */
+ trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Poll"));
+ }
+
+ /*
+ * Each pass through the following loop checks a follower for CBs.
+ * We are our own first follower. Any CBs found are moved to
+ * nocb_gp_head, where they await a grace period.
+ */
+ gotcbs = false;
+ smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */
+ for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
+ rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
+ if (!rdp->nocb_gp_head)
+ continue; /* No CBs here, try next follower. */
+
+ /* Move callbacks to wait-for-GP list, which is empty. */
+ WRITE_ONCE(rdp->nocb_head, NULL);
+ rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
+ gotcbs = true;
+ }
+
+ /* No callbacks? Sleep a bit if polling, and go retry. */
+ if (unlikely(!gotcbs)) {
+ WARN_ON(signal_pending(current));
+ if (rcu_nocb_poll) {
+ schedule_timeout_interruptible(1);
+ } else {
+ trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
+ TPS("WokeEmpty"));
+ }
+ goto wait_again;
+ }
+
+ /* Wait for one grace period. */
+ rcu_nocb_wait_gp(my_rdp);
+
+ /* Each pass through the following loop wakes a follower, if needed. */
+ for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
+ if (!rcu_nocb_poll &&
+ READ_ONCE(rdp->nocb_head) &&
+ READ_ONCE(my_rdp->nocb_leader_sleep)) {
+ raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
+ my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
+ raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
+ }
+ if (!rdp->nocb_gp_head)
+ continue; /* No CBs, so no need to wake follower. */
+
+ /* Append callbacks to follower's "done" list. */
+ raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+ tail = rdp->nocb_follower_tail;
+ rdp->nocb_follower_tail = rdp->nocb_gp_tail;
+ *tail = rdp->nocb_gp_head;
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
+ /* List was empty, so wake up the follower. */
+ swake_up_one(&rdp->nocb_wq);
+ }
+ }
+
+ /* If we (the leader) don't have CBs, go wait some more. */
+ if (!my_rdp->nocb_follower_head)
+ goto wait_again;
+}
+
+/*
+ * Followers come here to wait for additional callbacks to show up.
+ * This function does not return until callbacks appear.
+ */
+static void nocb_follower_wait(struct rcu_data *rdp)
+{
+ for (;;) {
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("FollowerSleep"));
+ swait_event_interruptible_exclusive(rdp->nocb_wq,
+ READ_ONCE(rdp->nocb_follower_head));
+ if (smp_load_acquire(&rdp->nocb_follower_head)) {
+ /* ^^^ Ensure CB invocation follows _head test. */
+ return;
+ }
+ WARN_ON(signal_pending(current));
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeEmpty"));
+ }
+}
+
+/*
+ * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
+ * callbacks queued by the corresponding no-CBs CPU, however, there is
+ * an optional leader-follower relationship so that the grace-period
+ * kthreads don't have to do quite so many wakeups.
+ */
+static int rcu_nocb_kthread(void *arg)
+{
+ int c, cl;
+ unsigned long flags;
+ struct rcu_head *list;
+ struct rcu_head *next;
+ struct rcu_head **tail;
+ struct rcu_data *rdp = arg;
+
+ /* Each pass through this loop invokes one batch of callbacks */
+ for (;;) {
+ /* Wait for callbacks. */
+ if (rdp->nocb_leader == rdp)
+ nocb_leader_wait(rdp);
+ else
+ nocb_follower_wait(rdp);
+
+ /* Pull the ready-to-invoke callbacks onto local list. */
+ raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+ list = rdp->nocb_follower_head;
+ rdp->nocb_follower_head = NULL;
+ tail = rdp->nocb_follower_tail;
+ rdp->nocb_follower_tail = &rdp->nocb_follower_head;
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ BUG_ON(!list);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeNonEmpty"));
+
+ /* Each pass through the following loop invokes a callback. */
+ trace_rcu_batch_start(rdp->rsp->name,
+ atomic_long_read(&rdp->nocb_q_count_lazy),
+ atomic_long_read(&rdp->nocb_q_count), -1);
+ c = cl = 0;
+ while (list) {
+ next = list->next;
+ /* Wait for enqueuing to complete, if needed. */
+ while (next == NULL && &list->next != tail) {
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WaitQueue"));
+ schedule_timeout_interruptible(1);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WokeQueue"));
+ next = list->next;
+ }
+ debug_rcu_head_unqueue(list);
+ local_bh_disable();
+ if (__rcu_reclaim(rdp->rsp->name, list))
+ cl++;
+ c++;
+ local_bh_enable();
+ cond_resched_tasks_rcu_qs();
+ list = next;
+ }
+ trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
+ smp_mb__before_atomic(); /* _add after CB invocation. */
+ atomic_long_add(-c, &rdp->nocb_q_count);
+ atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
+ }
+ return 0;
+}
+
+/* Is a deferred wakeup of rcu_nocb_kthread() required? */
+static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
+{
+ return READ_ONCE(rdp->nocb_defer_wakeup);
+}
+
+/* Do a deferred wakeup of rcu_nocb_kthread(). */
+static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
+{
+ unsigned long flags;
+ int ndw;
+
+ raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+ if (!rcu_nocb_need_deferred_wakeup(rdp)) {
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+ return;
+ }
+ ndw = READ_ONCE(rdp->nocb_defer_wakeup);
+ WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
+ __wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
+}
+
+/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
+static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
+{
+ struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
+
+ do_nocb_deferred_wakeup_common(rdp);
+}
+
+/*
+ * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
+ * This means we do an inexact common-case check. Note that if
+ * we miss, ->nocb_timer will eventually clean things up.
+ */
+static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
+{
+ if (rcu_nocb_need_deferred_wakeup(rdp))
+ do_nocb_deferred_wakeup_common(rdp);
+}
+
+void __init rcu_init_nohz(void)
+{
+ int cpu;
+ bool need_rcu_nocb_mask = false;
+ struct rcu_state *rsp;
+
+#if defined(CONFIG_NO_HZ_FULL)
+ if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
+ need_rcu_nocb_mask = true;
+#endif /* #if defined(CONFIG_NO_HZ_FULL) */
+
+ if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
+ if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
+ pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
+ return;
+ }
+ }
+ if (!cpumask_available(rcu_nocb_mask))
+ return;
+
+#if defined(CONFIG_NO_HZ_FULL)
+ if (tick_nohz_full_running)
+ cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
+#endif /* #if defined(CONFIG_NO_HZ_FULL) */
+
+ if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
+ pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
+ cpumask_and(rcu_nocb_mask, cpu_possible_mask,
+ rcu_nocb_mask);
+ }
+ if (cpumask_empty(rcu_nocb_mask))
+ pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
+ else
+ pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
+ cpumask_pr_args(rcu_nocb_mask));
+ if (rcu_nocb_poll)
+ pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
+
+ for_each_rcu_flavor(rsp) {
+ for_each_cpu(cpu, rcu_nocb_mask)
+ init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
+ rcu_organize_nocb_kthreads(rsp);
+ }
+}
+
+/* Initialize per-rcu_data variables for no-CBs CPUs. */
+static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
+{
+ rdp->nocb_tail = &rdp->nocb_head;
+ init_swait_queue_head(&rdp->nocb_wq);
+ rdp->nocb_follower_tail = &rdp->nocb_follower_head;
+ raw_spin_lock_init(&rdp->nocb_lock);
+ timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
+}
+
+/*
+ * If the specified CPU is a no-CBs CPU that does not already have its
+ * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
+ * brought online out of order, this can require re-organizing the
+ * leader-follower relationships.
+ */
+static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
+{
+ struct rcu_data *rdp;
+ struct rcu_data *rdp_last;
+ struct rcu_data *rdp_old_leader;
+ struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
+ struct task_struct *t;
+
+ /*
+ * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
+ * then nothing to do.
+ */
+ if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
+ return;
+
+ /* If we didn't spawn the leader first, reorganize! */
+ rdp_old_leader = rdp_spawn->nocb_leader;
+ if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
+ rdp_last = NULL;
+ rdp = rdp_old_leader;
+ do {
+ rdp->nocb_leader = rdp_spawn;
+ if (rdp_last && rdp != rdp_spawn)
+ rdp_last->nocb_next_follower = rdp;
+ if (rdp == rdp_spawn) {
+ rdp = rdp->nocb_next_follower;
+ } else {
+ rdp_last = rdp;
+ rdp = rdp->nocb_next_follower;
+ rdp_last->nocb_next_follower = NULL;
+ }
+ } while (rdp);
+ rdp_spawn->nocb_next_follower = rdp_old_leader;
+ }
+
+ /* Spawn the kthread for this CPU and RCU flavor. */
+ t = kthread_run(rcu_nocb_kthread, rdp_spawn,
+ "rcuo%c/%d", rsp->abbr, cpu);
+ BUG_ON(IS_ERR(t));
+ WRITE_ONCE(rdp_spawn->nocb_kthread, t);
+}
+
+/*
+ * If the specified CPU is a no-CBs CPU that does not already have its
+ * rcuo kthreads, spawn them.
+ */
+static void rcu_spawn_all_nocb_kthreads(int cpu)
+{
+ struct rcu_state *rsp;
+
+ if (rcu_scheduler_fully_active)
+ for_each_rcu_flavor(rsp)
+ rcu_spawn_one_nocb_kthread(rsp, cpu);
+}
+
+/*
+ * Once the scheduler is running, spawn rcuo kthreads for all online
+ * no-CBs CPUs. This assumes that the early_initcall()s happen before
+ * non-boot CPUs come online -- if this changes, we will need to add
+ * some mutual exclusion.
+ */
+static void __init rcu_spawn_nocb_kthreads(void)
+{
+ int cpu;
+
+ for_each_online_cpu(cpu)
+ rcu_spawn_all_nocb_kthreads(cpu);
+}
+
+/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
+static int rcu_nocb_leader_stride = -1;
+module_param(rcu_nocb_leader_stride, int, 0444);
+
+/*
+ * Initialize leader-follower relationships for all no-CBs CPU.
+ */
+static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
+{
+ int cpu;
+ int ls = rcu_nocb_leader_stride;
+ int nl = 0; /* Next leader. */
+ struct rcu_data *rdp;
+ struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
+ struct rcu_data *rdp_prev = NULL;
+
+ if (!cpumask_available(rcu_nocb_mask))
+ return;
+ if (ls == -1) {
+ ls = int_sqrt(nr_cpu_ids);
+ rcu_nocb_leader_stride = ls;
+ }
+
+ /*
+ * Each pass through this loop sets up one rcu_data structure.
+ * Should the corresponding CPU come online in the future, then
+ * we will spawn the needed set of rcu_nocb_kthread() kthreads.
+ */
+ for_each_cpu(cpu, rcu_nocb_mask) {
+ rdp = per_cpu_ptr(rsp->rda, cpu);
+ if (rdp->cpu >= nl) {
+ /* New leader, set up for followers & next leader. */
+ nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
+ rdp->nocb_leader = rdp;
+ rdp_leader = rdp;
+ } else {
+ /* Another follower, link to previous leader. */
+ rdp->nocb_leader = rdp_leader;
+ rdp_prev->nocb_next_follower = rdp;
+ }
+ rdp_prev = rdp;
+ }
+}
+
+/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
+static bool init_nocb_callback_list(struct rcu_data *rdp)
+{
+ if (!rcu_is_nocb_cpu(rdp->cpu))
+ return false;
+
+ /* If there are early-boot callbacks, move them to nocb lists. */
+ if (!rcu_segcblist_empty(&rdp->cblist)) {
+ rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
+ rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
+ atomic_long_set(&rdp->nocb_q_count,
+ rcu_segcblist_n_cbs(&rdp->cblist));
+ atomic_long_set(&rdp->nocb_q_count_lazy,
+ rcu_segcblist_n_lazy_cbs(&rdp->cblist));
+ rcu_segcblist_init(&rdp->cblist);
+ }
+ rcu_segcblist_disable(&rdp->cblist);
+ return true;
+}
+
+#else /* #ifdef CONFIG_RCU_NOCB_CPU */
+
+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
+{
+ WARN_ON_ONCE(1); /* Should be dead code. */
+ return false;
+}
+
+static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
+{
+}
+
+static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
+{
+ return NULL;
+}
+
+static void rcu_init_one_nocb(struct rcu_node *rnp)
+{
+}
+
+static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
+ bool lazy, unsigned long flags)
+{
+ return false;
+}
+
+static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
+ struct rcu_data *rdp,
+ unsigned long flags)
+{
+ return false;
+}
+
+static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
+{
+}
+
+static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
+{
+ return false;
+}
+
+static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
+{
+}
+
+static void rcu_spawn_all_nocb_kthreads(int cpu)
+{
+}
+
+static void __init rcu_spawn_nocb_kthreads(void)
+{
+}
+
+static bool init_nocb_callback_list(struct rcu_data *rdp)
+{
+ return false;
+}
+
+#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
+
+/*
+ * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
+ * grace-period kthread will do force_quiescent_state() processing?
+ * The idea is to avoid waking up RCU core processing on such a
+ * CPU unless the grace period has extended for too long.
+ *
+ * This code relies on the fact that all NO_HZ_FULL CPUs are also
+ * CONFIG_RCU_NOCB_CPU CPUs.
+ */
+static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
+{
+#ifdef CONFIG_NO_HZ_FULL
+ if (tick_nohz_full_cpu(smp_processor_id()) &&
+ (!rcu_gp_in_progress(rsp) ||
+ ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ)))
+ return true;
+#endif /* #ifdef CONFIG_NO_HZ_FULL */
+ return false;
+}
+
+/*
+ * Bind the RCU grace-period kthreads to the housekeeping CPU.
+ */
+static void rcu_bind_gp_kthread(void)
+{
+ if (!tick_nohz_full_enabled())
+ return;
+ housekeeping_affine(current, HK_FLAG_RCU);
+}
+
+/* Record the current task on dyntick-idle entry. */
+static void rcu_dynticks_task_enter(void)
+{
+#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
+ WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
+#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
+}
+
+/* Record no current task on dyntick-idle exit. */
+static void rcu_dynticks_task_exit(void)
+{
+#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
+ WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
+#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
+}