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- /*
- * 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, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- *
- * Copyright Red Hat, 2009
- * Copyright IBM Corporation, 2009
- *
- * Author: Ingo Molnar <mingo@elte.hu>
- * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
- */
- #include <linux/delay.h>
- #include <linux/gfp.h>
- #include <linux/oom.h>
- #include <linux/smpboot.h>
- #include <linux/tick.h>
- #define RCU_KTHREAD_PRIO 1
- #ifdef CONFIG_RCU_BOOST
- #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
- #else
- #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
- #endif
- #ifdef CONFIG_RCU_NOCB_CPU
- static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
- static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
- static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
- static char __initdata nocb_buf[NR_CPUS * 5];
- #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
- /*
- * Check the RCU kernel configuration parameters and print informative
- * messages about anything out of the ordinary. If you like #ifdef, you
- * will love this function.
- */
- static void __init rcu_bootup_announce_oddness(void)
- {
- #ifdef CONFIG_RCU_TRACE
- printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
- #endif
- #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
- printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
- CONFIG_RCU_FANOUT);
- #endif
- #ifdef CONFIG_RCU_FANOUT_EXACT
- printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
- #endif
- #ifdef CONFIG_RCU_FAST_NO_HZ
- printk(KERN_INFO
- "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
- #endif
- #ifdef CONFIG_PROVE_RCU
- printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
- #endif
- #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
- printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
- #endif
- #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
- printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
- #endif
- #if defined(CONFIG_RCU_CPU_STALL_INFO)
- printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
- #endif
- #if NUM_RCU_LVL_4 != 0
- printk(KERN_INFO "\tFour-level hierarchy is enabled.\n");
- #endif
- if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
- printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
- if (nr_cpu_ids != NR_CPUS)
- printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
- #ifdef CONFIG_RCU_NOCB_CPU
- #ifndef CONFIG_RCU_NOCB_CPU_NONE
- if (!have_rcu_nocb_mask) {
- zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
- have_rcu_nocb_mask = true;
- }
- #ifdef CONFIG_RCU_NOCB_CPU_ZERO
- pr_info("\tExperimental no-CBs CPU 0\n");
- cpumask_set_cpu(0, rcu_nocb_mask);
- #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
- #ifdef CONFIG_RCU_NOCB_CPU_ALL
- pr_info("\tExperimental no-CBs for all CPUs\n");
- cpumask_setall(rcu_nocb_mask);
- #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
- #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
- if (have_rcu_nocb_mask) {
- cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
- pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf);
- if (rcu_nocb_poll)
- pr_info("\tExperimental polled no-CBs CPUs.\n");
- }
- #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
- }
- #ifdef CONFIG_TREE_PREEMPT_RCU
- struct rcu_state rcu_preempt_state =
- RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
- DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
- static struct rcu_state *rcu_state = &rcu_preempt_state;
- static int rcu_preempted_readers_exp(struct rcu_node *rnp);
- /*
- * Tell them what RCU they are running.
- */
- static void __init rcu_bootup_announce(void)
- {
- printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
- rcu_bootup_announce_oddness();
- }
- /*
- * Return the number of RCU-preempt batches processed thus far
- * for debug and statistics.
- */
- long rcu_batches_completed_preempt(void)
- {
- return rcu_preempt_state.completed;
- }
- EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
- /*
- * Return the number of RCU batches processed thus far for debug & stats.
- */
- long rcu_batches_completed(void)
- {
- return rcu_batches_completed_preempt();
- }
- EXPORT_SYMBOL_GPL(rcu_batches_completed);
- /*
- * Force a quiescent state for preemptible RCU.
- */
- void rcu_force_quiescent_state(void)
- {
- force_quiescent_state(&rcu_preempt_state);
- }
- EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
- /*
- * Record a preemptible-RCU quiescent state for the specified CPU. Note
- * that this just means that the task currently running on the CPU is
- * not in a quiescent state. There might be any number of tasks blocked
- * while in an RCU read-side critical section.
- *
- * Unlike the other rcu_*_qs() functions, callers to this function
- * must disable irqs in order to protect the assignment to
- * ->rcu_read_unlock_special.
- */
- static void rcu_preempt_qs(int cpu)
- {
- struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
- if (rdp->passed_quiesce == 0)
- trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
- rdp->passed_quiesce = 1;
- current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
- }
- /*
- * We have entered the scheduler, and the current task might soon be
- * context-switched away from. If this task is in an RCU read-side
- * critical section, we will no longer be able to rely on the CPU to
- * record that fact, so we enqueue the task on the 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 preemption.
- */
- static void rcu_preempt_note_context_switch(int cpu)
- {
- struct task_struct *t = current;
- unsigned long flags;
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- if (t->rcu_read_lock_nesting > 0 &&
- (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
- /* Possibly blocking in an RCU read-side critical section. */
- rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
- rnp = rdp->mynode;
- raw_spin_lock_irqsave(&rnp->lock, flags);
- t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
- t->rcu_blocked_node = rnp;
- /*
- * If this CPU has already checked in, then this task
- * will hold up the next grace period rather than the
- * current grace period. Queue the task accordingly.
- * If the task is queued for the current grace period
- * (i.e., this CPU has not yet passed through a quiescent
- * state for the current grace period), then as long
- * as that task remains queued, the current grace period
- * cannot end. Note that there is some uncertainty as
- * to exactly when the current grace period started.
- * We take a conservative approach, which can result
- * in unnecessarily waiting on tasks that started very
- * slightly after the current grace period began. C'est
- * la vie!!!
- *
- * But first, note that the current CPU must still be
- * on line!
- */
- WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
- WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
- if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
- list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
- rnp->gp_tasks = &t->rcu_node_entry;
- #ifdef CONFIG_RCU_BOOST
- if (rnp->boost_tasks != NULL)
- rnp->boost_tasks = rnp->gp_tasks;
- #endif /* #ifdef CONFIG_RCU_BOOST */
- } else {
- list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
- if (rnp->qsmask & rdp->grpmask)
- rnp->gp_tasks = &t->rcu_node_entry;
- }
- trace_rcu_preempt_task(rdp->rsp->name,
- t->pid,
- (rnp->qsmask & rdp->grpmask)
- ? rnp->gpnum
- : rnp->gpnum + 1);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- } else if (t->rcu_read_lock_nesting < 0 &&
- t->rcu_read_unlock_special) {
- /*
- * 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.
- */
- local_irq_save(flags);
- rcu_preempt_qs(cpu);
- local_irq_restore(flags);
- }
- /*
- * 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;
- }
- /*
- * Record a quiescent state for all tasks that were previously queued
- * on the specified rcu_node structure and that were blocking the current
- * RCU grace period. The caller must hold the specified rnp->lock with
- * irqs disabled, and this lock is released upon return, but irqs remain
- * disabled.
- */
- static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
- __releases(rnp->lock)
- {
- unsigned long mask;
- struct rcu_node *rnp_p;
- if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- return; /* Still need more quiescent states! */
- }
- rnp_p = rnp->parent;
- if (rnp_p == NULL) {
- /*
- * Either there is only one rcu_node in the tree,
- * or tasks were kicked up to root rcu_node due to
- * CPUs going offline.
- */
- rcu_report_qs_rsp(&rcu_preempt_state, flags);
- return;
- }
- /* Report up the rest of the hierarchy. */
- mask = rnp->grpmask;
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
- raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
- rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
- }
- /*
- * 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;
- }
- /*
- * Handle special cases during rcu_read_unlock(), such as needing to
- * notify RCU core processing or task having blocked during the RCU
- * read-side critical section.
- */
- void rcu_read_unlock_special(struct task_struct *t)
- {
- int empty;
- int empty_exp;
- int empty_exp_now;
- unsigned long flags;
- struct list_head *np;
- #ifdef CONFIG_RCU_BOOST
- struct rt_mutex *rbmp = NULL;
- #endif /* #ifdef CONFIG_RCU_BOOST */
- struct rcu_node *rnp;
- int special;
- /* NMI handlers cannot block and cannot safely manipulate state. */
- if (in_nmi())
- return;
- local_irq_save(flags);
- /*
- * If RCU core is waiting for this CPU to exit critical section,
- * let it know that we have done so.
- */
- special = t->rcu_read_unlock_special;
- if (special & RCU_READ_UNLOCK_NEED_QS) {
- rcu_preempt_qs(smp_processor_id());
- }
- /* Hardware IRQ handlers cannot block. */
- if (in_irq() || in_serving_softirq()) {
- local_irq_restore(flags);
- return;
- }
- /* Clean up if blocked during RCU read-side critical section. */
- if (special & RCU_READ_UNLOCK_BLOCKED) {
- t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
- /*
- * Remove this task from the list it blocked on. The
- * task can migrate while we acquire the lock, but at
- * most one time. So at most two passes through loop.
- */
- for (;;) {
- rnp = t->rcu_blocked_node;
- raw_spin_lock(&rnp->lock); /* irqs already disabled. */
- if (rnp == t->rcu_blocked_node)
- break;
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
- }
- empty = !rcu_preempt_blocked_readers_cgp(rnp);
- empty_exp = !rcu_preempted_readers_exp(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("rcu_preempt",
- rnp->gpnum, t->pid);
- if (&t->rcu_node_entry == rnp->gp_tasks)
- rnp->gp_tasks = np;
- if (&t->rcu_node_entry == rnp->exp_tasks)
- rnp->exp_tasks = np;
- #ifdef CONFIG_RCU_BOOST
- if (&t->rcu_node_entry == rnp->boost_tasks)
- rnp->boost_tasks = np;
- /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
- if (t->rcu_boost_mutex) {
- rbmp = t->rcu_boost_mutex;
- t->rcu_boost_mutex = NULL;
- }
- #endif /* #ifdef CONFIG_RCU_BOOST */
- /*
- * 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 = !rcu_preempted_readers_exp(rnp);
- if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
- trace_rcu_quiescent_state_report("preempt_rcu",
- rnp->gpnum,
- 0, rnp->qsmask,
- rnp->level,
- rnp->grplo,
- rnp->grphi,
- !!rnp->gp_tasks);
- rcu_report_unblock_qs_rnp(rnp, flags);
- } else {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- }
- #ifdef CONFIG_RCU_BOOST
- /* Unboost if we were boosted. */
- if (rbmp)
- rt_mutex_unlock(rbmp);
- #endif /* #ifdef CONFIG_RCU_BOOST */
- /*
- * 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_preempt_state, rnp, true);
- } else {
- local_irq_restore(flags);
- }
- }
- #ifdef CONFIG_RCU_CPU_STALL_VERBOSE
- /*
- * Dump detailed information for all tasks blocking the current RCU
- * grace period on the specified rcu_node structure.
- */
- static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
- {
- unsigned long flags;
- struct task_struct *t;
- raw_spin_lock_irqsave(&rnp->lock, flags);
- if (!rcu_preempt_blocked_readers_cgp(rnp)) {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- return;
- }
- t = list_entry(rnp->gp_tasks,
- struct task_struct, rcu_node_entry);
- list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
- sched_show_task(t);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- }
- /*
- * Dump detailed information for all tasks blocking the current RCU
- * grace period.
- */
- static void rcu_print_detail_task_stall(struct rcu_state *rsp)
- {
- struct rcu_node *rnp = rcu_get_root(rsp);
- rcu_print_detail_task_stall_rnp(rnp);
- rcu_for_each_leaf_node(rsp, rnp)
- rcu_print_detail_task_stall_rnp(rnp);
- }
- #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
- static void rcu_print_detail_task_stall(struct rcu_state *rsp)
- {
- }
- #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
- #ifdef CONFIG_RCU_CPU_STALL_INFO
- static void rcu_print_task_stall_begin(struct rcu_node *rnp)
- {
- printk(KERN_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)
- {
- printk(KERN_CONT "\n");
- }
- #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
- static void rcu_print_task_stall_begin(struct rcu_node *rnp)
- {
- }
- static void rcu_print_task_stall_end(void)
- {
- }
- #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
- /*
- * 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,
- struct task_struct, rcu_node_entry);
- list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
- printk(KERN_CONT " P%d", t->pid);
- ndetected++;
- }
- rcu_print_task_stall_end();
- 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 ->gpnum, 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_node *rnp)
- {
- WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
- if (!list_empty(&rnp->blkd_tasks))
- rnp->gp_tasks = rnp->blkd_tasks.next;
- WARN_ON_ONCE(rnp->qsmask);
- }
- #ifdef CONFIG_HOTPLUG_CPU
- /*
- * Handle tasklist migration for case in which all CPUs covered by the
- * specified rcu_node have gone offline. Move them up to the root
- * rcu_node. The reason for not just moving them to the immediate
- * parent is to remove the need for rcu_read_unlock_special() to
- * make more than two attempts to acquire the target rcu_node's lock.
- * Returns true if there were tasks blocking the current RCU grace
- * period.
- *
- * Returns 1 if there was previously a task blocking the current grace
- * period on the specified rcu_node structure.
- *
- * The caller must hold rnp->lock with irqs disabled.
- */
- static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
- struct rcu_node *rnp,
- struct rcu_data *rdp)
- {
- struct list_head *lp;
- struct list_head *lp_root;
- int retval = 0;
- struct rcu_node *rnp_root = rcu_get_root(rsp);
- struct task_struct *t;
- if (rnp == rnp_root) {
- WARN_ONCE(1, "Last CPU thought to be offlined?");
- return 0; /* Shouldn't happen: at least one CPU online. */
- }
- /* If we are on an internal node, complain bitterly. */
- WARN_ON_ONCE(rnp != rdp->mynode);
- /*
- * Move tasks up to root rcu_node. Don't try to get fancy for
- * this corner-case operation -- just put this node's tasks
- * at the head of the root node's list, and update the root node's
- * ->gp_tasks and ->exp_tasks pointers to those of this node's,
- * if non-NULL. This might result in waiting for more tasks than
- * absolutely necessary, but this is a good performance/complexity
- * tradeoff.
- */
- if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
- retval |= RCU_OFL_TASKS_NORM_GP;
- if (rcu_preempted_readers_exp(rnp))
- retval |= RCU_OFL_TASKS_EXP_GP;
- lp = &rnp->blkd_tasks;
- lp_root = &rnp_root->blkd_tasks;
- while (!list_empty(lp)) {
- t = list_entry(lp->next, typeof(*t), rcu_node_entry);
- raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
- list_del(&t->rcu_node_entry);
- t->rcu_blocked_node = rnp_root;
- list_add(&t->rcu_node_entry, lp_root);
- if (&t->rcu_node_entry == rnp->gp_tasks)
- rnp_root->gp_tasks = rnp->gp_tasks;
- if (&t->rcu_node_entry == rnp->exp_tasks)
- rnp_root->exp_tasks = rnp->exp_tasks;
- #ifdef CONFIG_RCU_BOOST
- if (&t->rcu_node_entry == rnp->boost_tasks)
- rnp_root->boost_tasks = rnp->boost_tasks;
- #endif /* #ifdef CONFIG_RCU_BOOST */
- raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
- }
- rnp->gp_tasks = NULL;
- rnp->exp_tasks = NULL;
- #ifdef CONFIG_RCU_BOOST
- rnp->boost_tasks = NULL;
- /*
- * In case root is being boosted and leaf was not. Make sure
- * that we boost the tasks blocking the current grace period
- * in this case.
- */
- raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
- if (rnp_root->boost_tasks != NULL &&
- rnp_root->boost_tasks != rnp_root->gp_tasks &&
- rnp_root->boost_tasks != rnp_root->exp_tasks)
- rnp_root->boost_tasks = rnp_root->gp_tasks;
- raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
- #endif /* #ifdef CONFIG_RCU_BOOST */
- return retval;
- }
- #endif /* #ifdef CONFIG_HOTPLUG_CPU */
- /*
- * Check for a quiescent state from the current CPU. When a task blocks,
- * the task is recorded in the corresponding CPU's rcu_node structure,
- * which is checked elsewhere.
- *
- * Caller must disable hard irqs.
- */
- static void rcu_preempt_check_callbacks(int cpu)
- {
- struct task_struct *t = current;
- if (t->rcu_read_lock_nesting == 0) {
- rcu_preempt_qs(cpu);
- return;
- }
- if (t->rcu_read_lock_nesting > 0 &&
- per_cpu(rcu_preempt_data, cpu).qs_pending)
- t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
- }
- #ifdef CONFIG_RCU_BOOST
- static void rcu_preempt_do_callbacks(void)
- {
- rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
- }
- #endif /* #ifdef CONFIG_RCU_BOOST */
- /*
- * Queue a preemptible-RCU callback for invocation after a grace period.
- */
- void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
- {
- __call_rcu(head, func, &rcu_preempt_state, -1, 0);
- }
- EXPORT_SYMBOL_GPL(call_rcu);
- /*
- * Queue an RCU callback for lazy invocation after a grace period.
- * This will likely be later named something like "call_rcu_lazy()",
- * but this change will require some way of tagging the lazy RCU
- * callbacks in the list of pending callbacks. Until then, this
- * function may only be called from __kfree_rcu().
- */
- void kfree_call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *rcu))
- {
- __call_rcu(head, func, &rcu_preempt_state, -1, 1);
- }
- EXPORT_SYMBOL_GPL(kfree_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.
- */
- void synchronize_rcu(void)
- {
- rcu_lockdep_assert(!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)
- return;
- if (rcu_expedited)
- synchronize_rcu_expedited();
- else
- wait_rcu_gp(call_rcu);
- }
- EXPORT_SYMBOL_GPL(synchronize_rcu);
- static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
- static unsigned long sync_rcu_preempt_exp_count;
- static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
- /*
- * Return non-zero if there are any tasks in RCU read-side critical
- * sections blocking the current preemptible-RCU expedited grace period.
- * If there is no preemptible-RCU expedited grace period currently in
- * progress, returns zero unconditionally.
- */
- static int rcu_preempted_readers_exp(struct rcu_node *rnp)
- {
- return rnp->exp_tasks != NULL;
- }
- /*
- * return non-zero if there is no RCU expedited grace period in progress
- * for the specified rcu_node structure, in other words, if all CPUs and
- * tasks covered by the specified rcu_node structure have done their bit
- * for the current expedited grace period. Works only for preemptible
- * RCU -- other RCU implementation use other means.
- *
- * Caller must hold sync_rcu_preempt_exp_mutex.
- */
- static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
- {
- return !rcu_preempted_readers_exp(rnp) &&
- ACCESS_ONCE(rnp->expmask) == 0;
- }
- /*
- * Report the exit from RCU read-side critical section for the last task
- * that queued itself during or before the current expedited preemptible-RCU
- * grace period. This event is reported either to the rcu_node structure on
- * which the task was queued or to one of that rcu_node structure's ancestors,
- * recursively up the tree. (Calm down, calm down, we do the recursion
- * iteratively!)
- *
- * Most callers will set the "wake" flag, but the task initiating the
- * expedited grace period need not wake itself.
- *
- * Caller must hold sync_rcu_preempt_exp_mutex.
- */
- static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
- bool wake)
- {
- unsigned long flags;
- unsigned long mask;
- raw_spin_lock_irqsave(&rnp->lock, flags);
- for (;;) {
- if (!sync_rcu_preempt_exp_done(rnp)) {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- break;
- }
- if (rnp->parent == NULL) {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- if (wake)
- wake_up(&sync_rcu_preempt_exp_wq);
- break;
- }
- mask = rnp->grpmask;
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
- rnp = rnp->parent;
- raw_spin_lock(&rnp->lock); /* irqs already disabled */
- rnp->expmask &= ~mask;
- }
- }
- /*
- * Snapshot the tasks blocking the newly started preemptible-RCU expedited
- * grace period for the specified rcu_node structure. If there are no such
- * tasks, report it up the rcu_node hierarchy.
- *
- * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
- * CPU hotplug operations.
- */
- static void
- sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
- {
- unsigned long flags;
- int must_wait = 0;
- raw_spin_lock_irqsave(&rnp->lock, flags);
- if (list_empty(&rnp->blkd_tasks)) {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- } else {
- rnp->exp_tasks = rnp->blkd_tasks.next;
- rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
- must_wait = 1;
- }
- if (!must_wait)
- rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
- }
- /**
- * synchronize_rcu_expedited - Brute-force RCU grace period
- *
- * Wait for an RCU-preempt grace period, but expedite it. The basic
- * idea is to invoke synchronize_sched_expedited() to push all the tasks to
- * the ->blkd_tasks lists and wait for this list to drain. This consumes
- * significant time on all CPUs and is unfriendly to real-time workloads,
- * so is thus not recommended for any sort of common-case code.
- * In fact, if you are using synchronize_rcu_expedited() in a loop,
- * please restructure your code to batch your updates, and then Use a
- * single synchronize_rcu() instead.
- *
- * Note that it is illegal to call this function while holding any lock
- * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
- * to call this function from a CPU-hotplug notifier. Failing to observe
- * these restriction will result in deadlock.
- */
- void synchronize_rcu_expedited(void)
- {
- unsigned long flags;
- struct rcu_node *rnp;
- struct rcu_state *rsp = &rcu_preempt_state;
- unsigned long snap;
- int trycount = 0;
- smp_mb(); /* Caller's modifications seen first by other CPUs. */
- snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
- smp_mb(); /* Above access cannot bleed into critical section. */
- /*
- * Block CPU-hotplug operations. This means that any CPU-hotplug
- * operation that finds an rcu_node structure with tasks in the
- * process of being boosted will know that all tasks blocking
- * this expedited grace period will already be in the process of
- * being boosted. This simplifies the process of moving tasks
- * from leaf to root rcu_node structures.
- */
- get_online_cpus();
- /*
- * Acquire lock, falling back to synchronize_rcu() if too many
- * lock-acquisition failures. Of course, if someone does the
- * expedited grace period for us, just leave.
- */
- while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
- if (ULONG_CMP_LT(snap,
- ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
- put_online_cpus();
- goto mb_ret; /* Others did our work for us. */
- }
- if (trycount++ < 10) {
- udelay(trycount * num_online_cpus());
- } else {
- put_online_cpus();
- wait_rcu_gp(call_rcu);
- return;
- }
- }
- if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
- put_online_cpus();
- goto unlock_mb_ret; /* Others did our work for us. */
- }
- /* force all RCU readers onto ->blkd_tasks lists. */
- synchronize_sched_expedited();
- /* Initialize ->expmask for all non-leaf rcu_node structures. */
- rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
- raw_spin_lock_irqsave(&rnp->lock, flags);
- rnp->expmask = rnp->qsmaskinit;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- }
- /* Snapshot current state of ->blkd_tasks lists. */
- rcu_for_each_leaf_node(rsp, rnp)
- sync_rcu_preempt_exp_init(rsp, rnp);
- if (NUM_RCU_NODES > 1)
- sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
- put_online_cpus();
- /* Wait for snapshotted ->blkd_tasks lists to drain. */
- rnp = rcu_get_root(rsp);
- wait_event(sync_rcu_preempt_exp_wq,
- sync_rcu_preempt_exp_done(rnp));
- /* Clean up and exit. */
- smp_mb(); /* ensure expedited GP seen before counter increment. */
- ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
- unlock_mb_ret:
- mutex_unlock(&sync_rcu_preempt_exp_mutex);
- mb_ret:
- smp_mb(); /* ensure subsequent action seen after grace period. */
- }
- EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
- /**
- * 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_preempt_state);
- }
- EXPORT_SYMBOL_GPL(rcu_barrier);
- /*
- * Initialize preemptible RCU's state structures.
- */
- static void __init __rcu_init_preempt(void)
- {
- rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
- }
- #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
- static struct rcu_state *rcu_state = &rcu_sched_state;
- /*
- * Tell them what RCU they are running.
- */
- static void __init rcu_bootup_announce(void)
- {
- printk(KERN_INFO "Hierarchical RCU implementation.\n");
- rcu_bootup_announce_oddness();
- }
- /*
- * Return the number of RCU batches processed thus far for debug & stats.
- */
- long rcu_batches_completed(void)
- {
- return rcu_batches_completed_sched();
- }
- EXPORT_SYMBOL_GPL(rcu_batches_completed);
- /*
- * Force a quiescent state for RCU, which, because there is no preemptible
- * RCU, becomes the same as rcu-sched.
- */
- void rcu_force_quiescent_state(void)
- {
- rcu_sched_force_quiescent_state();
- }
- EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
- /*
- * Because preemptible RCU does not exist, we never have to check for
- * CPUs being in quiescent states.
- */
- static void rcu_preempt_note_context_switch(int cpu)
- {
- }
- /*
- * 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;
- }
- #ifdef CONFIG_HOTPLUG_CPU
- /* Because preemptible RCU does not exist, no quieting of tasks. */
- static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
- {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- }
- #endif /* #ifdef CONFIG_HOTPLUG_CPU */
- /*
- * 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 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_node *rnp)
- {
- WARN_ON_ONCE(rnp->qsmask);
- }
- #ifdef CONFIG_HOTPLUG_CPU
- /*
- * Because preemptible RCU does not exist, it never needs to migrate
- * tasks that were blocked within RCU read-side critical sections, and
- * such non-existent tasks cannot possibly have been blocking the current
- * grace period.
- */
- static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
- struct rcu_node *rnp,
- struct rcu_data *rdp)
- {
- return 0;
- }
- #endif /* #ifdef CONFIG_HOTPLUG_CPU */
- /*
- * Because preemptible RCU does not exist, it never has any callbacks
- * to check.
- */
- static void rcu_preempt_check_callbacks(int cpu)
- {
- }
- /*
- * Queue an RCU callback for lazy invocation after a grace period.
- * This will likely be later named something like "call_rcu_lazy()",
- * but this change will require some way of tagging the lazy RCU
- * callbacks in the list of pending callbacks. Until then, this
- * function may only be called from __kfree_rcu().
- *
- * Because there is no preemptible RCU, we use RCU-sched instead.
- */
- void kfree_call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *rcu))
- {
- __call_rcu(head, func, &rcu_sched_state, -1, 1);
- }
- EXPORT_SYMBOL_GPL(kfree_call_rcu);
- /*
- * Wait for an rcu-preempt grace period, but make it happen quickly.
- * But because preemptible RCU does not exist, map to rcu-sched.
- */
- void synchronize_rcu_expedited(void)
- {
- synchronize_sched_expedited();
- }
- EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
- #ifdef CONFIG_HOTPLUG_CPU
- /*
- * Because preemptible RCU does not exist, there is never any need to
- * report on tasks preempted in RCU read-side critical sections during
- * expedited RCU grace periods.
- */
- static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
- bool wake)
- {
- }
- #endif /* #ifdef CONFIG_HOTPLUG_CPU */
- /*
- * 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)
- {
- }
- #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
- #ifdef CONFIG_RCU_BOOST
- #include "rtmutex_common.h"
- #ifdef CONFIG_RCU_TRACE
- static void rcu_initiate_boost_trace(struct rcu_node *rnp)
- {
- if (list_empty(&rnp->blkd_tasks))
- rnp->n_balk_blkd_tasks++;
- else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
- rnp->n_balk_exp_gp_tasks++;
- else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
- rnp->n_balk_boost_tasks++;
- else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
- rnp->n_balk_notblocked++;
- else if (rnp->gp_tasks != NULL &&
- ULONG_CMP_LT(jiffies, rnp->boost_time))
- rnp->n_balk_notyet++;
- else
- rnp->n_balk_nos++;
- }
- #else /* #ifdef CONFIG_RCU_TRACE */
- static void rcu_initiate_boost_trace(struct rcu_node *rnp)
- {
- }
- #endif /* #else #ifdef CONFIG_RCU_TRACE */
- 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 rt_mutex mtx;
- struct task_struct *t;
- struct list_head *tb;
- if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
- return 0; /* Nothing left to boost. */
- raw_spin_lock_irqsave(&rnp->lock, 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(&rnp->lock, 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;
- rnp->n_exp_boosts++;
- } else {
- tb = rnp->boost_tasks;
- rnp->n_normal_boosts++;
- }
- rnp->n_tasks_boosted++;
- /*
- * 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(&mtx, t);
- t->rcu_boost_mutex = &mtx;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
- rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
- return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
- ACCESS_ONCE(rnp->boost_tasks) != NULL;
- }
- /*
- * Priority-boosting kthread. One per leaf rcu_node and one for the
- * root 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("Start boost kthread@init");
- for (;;) {
- rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
- trace_rcu_utilization("End boost kthread@rcu_wait");
- rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
- trace_rcu_utilization("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("End boost kthread@rcu_yield");
- schedule_timeout_interruptible(2);
- trace_rcu_utilization("Start boost kthread@rcu_yield");
- spincnt = 0;
- }
- }
- /* NOTREACHED */
- trace_rcu_utilization("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)
- {
- struct task_struct *t;
- if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
- rnp->n_balk_exp_gp_tasks++;
- raw_spin_unlock_irqrestore(&rnp->lock, 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(&rnp->lock, flags);
- t = rnp->boost_kthread_task;
- if (t)
- rcu_wake_cond(t, rnp->boost_kthread_status);
- } else {
- rcu_initiate_boost_trace(rnp);
- raw_spin_unlock_irqrestore(&rnp->lock, 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 __get_cpu_var(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 __cpuinit 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_preempt_state != rsp)
- return 0;
- if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 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(&rnp->lock, flags);
- rnp->boost_kthread_task = t;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- sp.sched_priority = RCU_BOOST_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, &__get_cpu_var(rcu_sched_data));
- rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
- rcu_preempt_do_callbacks();
- }
- static void rcu_cpu_kthread_setup(unsigned int cpu)
- {
- struct sched_param sp;
- sp.sched_priority = RCU_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 __get_cpu_var(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 = &__get_cpu_var(rcu_cpu_kthread_status);
- char work, *workp = &__get_cpu_var(rcu_cpu_has_work);
- int spincnt;
- for (spincnt = 0; spincnt < 10; spincnt++) {
- trace_rcu_utilization("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("End CPU kthread@rcu_wait");
- *statusp = RCU_KTHREAD_WAITING;
- return;
- }
- }
- *statusp = RCU_KTHREAD_YIELDING;
- trace_rcu_utilization("Start CPU kthread@rcu_yield");
- schedule_timeout_interruptible(2);
- trace_rcu_utilization("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 = rnp->qsmaskinit;
- cpumask_var_t cm;
- int cpu;
- if (!t)
- return;
- if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
- return;
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
- if ((mask & 0x1) && cpu != outgoingcpu)
- cpumask_set_cpu(cpu, cm);
- if (cpumask_weight(cm) == 0) {
- cpumask_setall(cm);
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
- cpumask_clear_cpu(cpu, cm);
- WARN_ON_ONCE(cpumask_weight(cm) == 0);
- }
- 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 all kthreads -- called as soon as the scheduler is running.
- */
- static int __init rcu_spawn_kthreads(void)
- {
- struct rcu_node *rnp;
- int cpu;
- rcu_scheduler_fully_active = 1;
- for_each_possible_cpu(cpu)
- per_cpu(rcu_cpu_has_work, cpu) = 0;
- BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
- rnp = rcu_get_root(rcu_state);
- (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
- if (NUM_RCU_NODES > 1) {
- rcu_for_each_leaf_node(rcu_state, rnp)
- (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
- }
- return 0;
- }
- early_initcall(rcu_spawn_kthreads);
- static void __cpuinit rcu_prepare_kthreads(int cpu)
- {
- struct rcu_data *rdp = per_cpu_ptr(rcu_state->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, rnp);
- }
- #else /* #ifdef CONFIG_RCU_BOOST */
- static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
- {
- raw_spin_unlock_irqrestore(&rnp->lock, 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 int __init rcu_scheduler_really_started(void)
- {
- rcu_scheduler_fully_active = 1;
- return 0;
- }
- early_initcall(rcu_scheduler_really_started);
- static void __cpuinit 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(int cpu, unsigned long *delta_jiffies)
- {
- *delta_jiffies = ULONG_MAX;
- return rcu_cpu_has_callbacks(cpu, NULL);
- }
- /*
- * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
- * after it.
- */
- static void rcu_cleanup_after_idle(int cpu)
- {
- }
- /*
- * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
- * is nothing.
- */
- static void rcu_prepare_for_idle(int cpu)
- {
- }
- /*
- * 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);
- extern int tick_nohz_enabled;
- /*
- * Try to advance callbacks for all flavors of RCU on the current CPU.
- * Afterwards, if there are any callbacks ready for immediate invocation,
- * return true.
- */
- static bool rcu_try_advance_all_cbs(void)
- {
- bool cbs_ready = false;
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- struct rcu_state *rsp;
- 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 (rdp->completed != rnp->completed &&
- rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
- rcu_process_gp_end(rsp, rdp);
- if (cpu_has_callbacks_ready_to_invoke(rdp))
- 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(int cpu, unsigned long *dj)
- {
- struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
- /* 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(cpu, &rdtp->all_lazy)) {
- *dj = ULONG_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;
- }
- 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(int cpu)
- {
- struct rcu_data *rdp;
- struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
- struct rcu_node *rnp;
- struct rcu_state *rsp;
- int tne;
- /* Handle nohz enablement switches conservatively. */
- tne = ACCESS_ONCE(tick_nohz_enabled);
- if (tne != rdtp->tick_nohz_enabled_snap) {
- if (rcu_cpu_has_callbacks(cpu, NULL))
- invoke_rcu_core(); /* force nohz to see update. */
- rdtp->tick_nohz_enabled_snap = tne;
- return;
- }
- if (!tne)
- return;
- /* If this is a no-CBs CPU, no callbacks, just return. */
- if (rcu_is_nocb_cpu(cpu))
- 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) {
- 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 = per_cpu_ptr(rsp->rda, cpu);
- if (!*rdp->nxttail[RCU_DONE_TAIL])
- continue;
- rnp = rdp->mynode;
- raw_spin_lock(&rnp->lock); /* irqs already disabled. */
- rcu_accelerate_cbs(rsp, rnp, rdp);
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
- }
- }
- /*
- * 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(int cpu)
- {
- struct rcu_data *rdp;
- struct rcu_state *rsp;
- if (rcu_is_nocb_cpu(cpu))
- return;
- rcu_try_advance_all_cbs();
- for_each_rcu_flavor(rsp) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
- if (cpu_has_callbacks_ready_to_invoke(rdp))
- 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 = __this_cpu_ptr(rsp->rda);
- if (rdp->qlen_lazy != 0) {
- 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);
- /*
- * Prevent premature wakeup: ensure that all increments happen
- * before there is a chance of the counter reaching zero.
- */
- atomic_set(&oom_callback_count, 1);
- get_online_cpus();
- for_each_online_cpu(cpu) {
- smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
- cond_resched();
- }
- put_online_cpus();
- /* 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_CPU_STALL_INFO
- #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)
- {
- printk(KERN_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)
- {
- 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;
- if (rsp->gpnum == rdp->gpnum) {
- ticks_title = "ticks this GP";
- ticks_value = rdp->ticks_this_gp;
- } else {
- ticks_title = "GPs behind";
- ticks_value = rsp->gpnum - rdp->gpnum;
- }
- print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
- printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
- cpu, ticks_value, ticks_title,
- atomic_read(&rdtp->dynticks) & 0xfff,
- rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
- rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
- fast_no_hz);
- }
- /* Terminate the stall-info list. */
- static void print_cpu_stall_info_end(void)
- {
- printk(KERN_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)
- __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
- }
- #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
- static void print_cpu_stall_info_begin(void)
- {
- printk(KERN_CONT " {");
- }
- static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
- {
- printk(KERN_CONT " %d", cpu);
- }
- static void print_cpu_stall_info_end(void)
- {
- printk(KERN_CONT "} ");
- }
- static void zero_cpu_stall_ticks(struct rcu_data *rdp)
- {
- }
- static void increment_cpu_stall_ticks(void)
- {
- }
- #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
- #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);
- have_rcu_nocb_mask = true;
- 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 = 1;
- return 0;
- }
- early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
- /*
- * Do any no-CBs CPUs need another grace period?
- *
- * Interrupts must be disabled. If the caller does not hold the root
- * rnp_node structure's ->lock, the results are advisory only.
- */
- static int rcu_nocb_needs_gp(struct rcu_state *rsp)
- {
- struct rcu_node *rnp = rcu_get_root(rsp);
- return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
- }
- /*
- * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
- * grace period.
- */
- static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
- {
- wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
- }
- /*
- * Set the root rcu_node structure's ->need_future_gp field
- * based on the sum of those of all rcu_node structures. This does
- * double-count the root rcu_node structure's requests, but this
- * is necessary to handle the possibility of a rcu_nocb_kthread()
- * having awakened during the time that the rcu_node structures
- * were being updated for the end of the previous grace period.
- */
- static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
- {
- rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
- }
- static void rcu_init_one_nocb(struct rcu_node *rnp)
- {
- init_waitqueue_head(&rnp->nocb_gp_wq[0]);
- init_waitqueue_head(&rnp->nocb_gp_wq[1]);
- }
- /* Is the specified CPU a no-CPUs CPU? */
- bool rcu_is_nocb_cpu(int cpu)
- {
- if (have_rcu_nocb_mask)
- return cpumask_test_cpu(cpu, rcu_nocb_mask);
- return false;
- }
- /*
- * 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)
- {
- int len;
- struct rcu_head **old_rhpp;
- struct task_struct *t;
- /* Enqueue the callback on the nocb list and update counts. */
- old_rhpp = xchg(&rdp->nocb_tail, rhtp);
- ACCESS_ONCE(*old_rhpp) = rhp;
- atomic_long_add(rhcount, &rdp->nocb_q_count);
- atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
- /* If we are not being polled and there is a kthread, awaken it ... */
- t = ACCESS_ONCE(rdp->nocb_kthread);
- if (rcu_nocb_poll | !t)
- return;
- len = atomic_long_read(&rdp->nocb_q_count);
- if (old_rhpp == &rdp->nocb_head) {
- wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */
- rdp->qlen_last_fqs_check = 0;
- } else if (len > rdp->qlen_last_fqs_check + qhimark) {
- wake_up_process(t); /* ... or if many callbacks queued. */
- rdp->qlen_last_fqs_check = LONG_MAX / 2;
- }
- 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)
- {
- if (!rcu_is_nocb_cpu(rdp->cpu))
- return 0;
- __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
- if (__is_kfree_rcu_offset((unsigned long)rhp->func))
- trace_rcu_kfree_callback(rdp->rsp->name, rhp,
- (unsigned long)rhp->func,
- rdp->qlen_lazy, rdp->qlen);
- else
- trace_rcu_callback(rdp->rsp->name, rhp,
- rdp->qlen_lazy, rdp->qlen);
- return 1;
- }
- /*
- * 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_state *rsp,
- struct rcu_data *rdp)
- {
- long ql = rsp->qlen;
- long qll = rsp->qlen_lazy;
- /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
- if (!rcu_is_nocb_cpu(smp_processor_id()))
- return 0;
- rsp->qlen = 0;
- rsp->qlen_lazy = 0;
- /* First, enqueue the donelist, if any. This preserves CB ordering. */
- if (rsp->orphan_donelist != NULL) {
- __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
- rsp->orphan_donetail, ql, qll);
- ql = qll = 0;
- rsp->orphan_donelist = NULL;
- rsp->orphan_donetail = &rsp->orphan_donelist;
- }
- if (rsp->orphan_nxtlist != NULL) {
- __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
- rsp->orphan_nxttail, ql, qll);
- ql = qll = 0;
- rsp->orphan_nxtlist = NULL;
- rsp->orphan_nxttail = &rsp->orphan_nxtlist;
- }
- return 1;
- }
- /*
- * 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;
- struct rcu_node *rnp = rdp->mynode;
- raw_spin_lock_irqsave(&rnp->lock, flags);
- c = rcu_start_future_gp(rnp, rdp);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- /*
- * Wait for the grace period. Do so interruptibly to avoid messing
- * up the load average.
- */
- trace_rcu_future_gp(rnp, rdp, c, "StartWait");
- for (;;) {
- wait_event_interruptible(
- rnp->nocb_gp_wq[c & 0x1],
- (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
- if (likely(d))
- break;
- flush_signals(current);
- trace_rcu_future_gp(rnp, rdp, c, "ResumeWait");
- }
- trace_rcu_future_gp(rnp, rdp, c, "EndWait");
- smp_mb(); /* Ensure that CB invocation happens after GP end. */
- }
- /*
- * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
- * callbacks queued by the corresponding no-CBs CPU.
- */
- static int rcu_nocb_kthread(void *arg)
- {
- int c, cl;
- 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 (;;) {
- /* If not polling, wait for next batch of callbacks. */
- if (!rcu_nocb_poll)
- wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
- list = ACCESS_ONCE(rdp->nocb_head);
- if (!list) {
- schedule_timeout_interruptible(1);
- flush_signals(current);
- continue;
- }
- /*
- * Extract queued callbacks, update counts, and wait
- * for a grace period to elapse.
- */
- ACCESS_ONCE(rdp->nocb_head) = NULL;
- tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
- c = atomic_long_xchg(&rdp->nocb_q_count, 0);
- cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
- ACCESS_ONCE(rdp->nocb_p_count) += c;
- ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
- rcu_nocb_wait_gp(rdp);
- /* Each pass through the following loop invokes a callback. */
- trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
- c = cl = 0;
- while (list) {
- next = list->next;
- /* Wait for enqueuing to complete, if needed. */
- while (next == NULL && &list->next != tail) {
- schedule_timeout_interruptible(1);
- next = list->next;
- }
- debug_rcu_head_unqueue(list);
- local_bh_disable();
- if (__rcu_reclaim(rdp->rsp->name, list))
- cl++;
- c++;
- local_bh_enable();
- list = next;
- }
- trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
- ACCESS_ONCE(rdp->nocb_p_count) -= c;
- ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
- rdp->n_nocbs_invoked += c;
- }
- return 0;
- }
- /* 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_waitqueue_head(&rdp->nocb_wq);
- }
- /* Create a kthread for each RCU flavor for each no-CBs CPU. */
- static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
- {
- int cpu;
- struct rcu_data *rdp;
- struct task_struct *t;
- if (rcu_nocb_mask == NULL)
- return;
- for_each_cpu(cpu, rcu_nocb_mask) {
- rdp = per_cpu_ptr(rsp->rda, cpu);
- t = kthread_run(rcu_nocb_kthread, rdp,
- "rcuo%c/%d", rsp->abbr, cpu);
- BUG_ON(IS_ERR(t));
- ACCESS_ONCE(rdp->nocb_kthread) = t;
- }
- }
- /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
- static bool init_nocb_callback_list(struct rcu_data *rdp)
- {
- if (rcu_nocb_mask == NULL ||
- !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
- return false;
- rdp->nxttail[RCU_NEXT_TAIL] = NULL;
- return true;
- }
- #else /* #ifdef CONFIG_RCU_NOCB_CPU */
- static int rcu_nocb_needs_gp(struct rcu_state *rsp)
- {
- return 0;
- }
- static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
- {
- }
- static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
- {
- }
- 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)
- {
- return 0;
- }
- static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
- struct rcu_data *rdp)
- {
- return 0;
- }
- static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
- {
- }
- static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
- {
- }
- static bool init_nocb_callback_list(struct rcu_data *rdp)
- {
- return false;
- }
- #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
- /*
- * An adaptive-ticks CPU can potentially execute in kernel mode for an
- * arbitrarily long period of time with the scheduling-clock tick turned
- * off. RCU will be paying attention to this CPU because it is in the
- * kernel, but the CPU cannot be guaranteed to be executing the RCU state
- * machine because the scheduling-clock tick has been disabled. Therefore,
- * if an adaptive-ticks CPU is failing to respond to the current grace
- * period and has not be idle from an RCU perspective, kick it.
- */
- static void rcu_kick_nohz_cpu(int cpu)
- {
- #ifdef CONFIG_NO_HZ_FULL
- if (tick_nohz_full_cpu(cpu))
- smp_send_reschedule(cpu);
- #endif /* #ifdef CONFIG_NO_HZ_FULL */
- }
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