/*
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
* Internal non-public definitions that provide either classic
- * or preemptable semantics.
+ * 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
#ifdef CONFIG_TREE_PREEMPT_RCU
-struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
+struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt);
DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
+static struct rcu_state *rcu_state = &rcu_preempt_state;
+static void rcu_read_unlock_special(struct task_struct *t);
static int rcu_preempted_readers_exp(struct rcu_node *rnp);
/*
*/
static void __init rcu_bootup_announce(void)
{
- printk(KERN_INFO "Preemptable hierarchical RCU implementation.\n");
+ printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
- * Record a preemptable-RCU quiescent state for the specified CPU. Note
+ * 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.
rdp->passed_quiesc_completed = rdp->gpnum - 1;
barrier();
+ if (rdp->passed_quiesc == 0)
+ trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
rdp->passed_quiesc = 1;
current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
}
struct rcu_data *rdp;
struct rcu_node *rnp;
- if (t->rcu_read_lock_nesting &&
+ 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. */
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);
}
/*
}
/*
- * Tree-preemptable RCU implementation for rcu_read_lock().
+ * Tree-preemptible RCU implementation for rcu_read_lock().
* Just increment ->rcu_read_lock_nesting, shared state will be updated
* if we block.
*/
* for the specified rcu_node structure. If the caller needs a reliable
* answer, it must hold the rcu_node's ->lock.
*/
-static int rcu_preempted_readers(struct rcu_node *rnp)
+static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
{
return rnp->gp_tasks != NULL;
}
unsigned long mask;
struct rcu_node *rnp_p;
- if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
+ if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return; /* Still need more quiescent states! */
}
* 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)
+static noinline void rcu_read_unlock_special(struct task_struct *t)
{
int empty;
int empty_exp;
}
/* Hardware IRQ handlers cannot block. */
- if (in_irq()) {
+ if (in_irq() || in_serving_softirq()) {
local_irq_restore(flags);
return;
}
break;
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
- empty = !rcu_preempted_readers(rnp);
+ 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);
+ 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 and clear ->rcu_boosted with rcu_node lock held. */
+ if (t->rcu_boosted) {
+ special |= RCU_READ_UNLOCK_BOOSTED;
+ t->rcu_boosted = 0;
+ }
+#endif /* #ifdef CONFIG_RCU_BOOST */
t->rcu_blocked_node = NULL;
/*
* we aren't waiting on any CPUs, report the quiescent state.
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock.
*/
- if (empty)
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- else
+ 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 (special & RCU_READ_UNLOCK_BOOSTED) {
+ rt_mutex_unlock(t->rcu_boost_mutex);
+ t->rcu_boost_mutex = NULL;
+ }
+#endif /* #ifdef CONFIG_RCU_BOOST */
/*
* If this was the last task on the expedited lists,
}
/*
- * Tree-preemptable RCU implementation for rcu_read_unlock().
+ * Tree-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
struct task_struct *t = current;
barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */
- --t->rcu_read_lock_nesting;
- barrier(); /* decrement before load of ->rcu_read_unlock_special */
- if (t->rcu_read_lock_nesting == 0 &&
- unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
- rcu_read_unlock_special(t);
+ if (t->rcu_read_lock_nesting != 1)
+ --t->rcu_read_lock_nesting;
+ else {
+ t->rcu_read_lock_nesting = INT_MIN;
+ barrier(); /* assign before ->rcu_read_unlock_special load */
+ if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
+ rcu_read_unlock_special(t);
+ barrier(); /* ->rcu_read_unlock_special load before assign */
+ t->rcu_read_lock_nesting = 0;
+ }
#ifdef CONFIG_PROVE_LOCKING
- WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
+ {
+ int rrln = ACCESS_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);
unsigned long flags;
struct task_struct *t;
- if (!rcu_preempted_readers(rnp))
+ if (!rcu_preempt_blocked_readers_cgp(rnp))
return;
raw_spin_lock_irqsave(&rnp->lock, flags);
t = list_entry(rnp->gp_tasks,
{
struct task_struct *t;
- if (!rcu_preempted_readers(rnp))
+ if (!rcu_preempt_blocked_readers_cgp(rnp))
return;
t = list_entry(rnp->gp_tasks,
struct task_struct, rcu_node_entry);
*/
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
- WARN_ON_ONCE(rcu_preempted_readers(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);
* absolutely necessary, but this is a good performance/complexity
* tradeoff.
*/
- if (rcu_preempted_readers(rnp))
+ if (rcu_preempt_blocked_readers_cgp(rnp))
retval |= RCU_OFL_TASKS_NORM_GP;
if (rcu_preempted_readers_exp(rnp))
retval |= RCU_OFL_TASKS_EXP_GP;
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 */
}
+
+#ifdef CONFIG_RCU_BOOST
+ /* In case root is being boosted and leaf is not. */
+ 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->gp_tasks;
+ raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
rnp->gp_tasks = NULL;
rnp->exp_tasks = NULL;
return retval;
}
/*
- * Do CPU-offline processing for preemptable RCU.
+ * Do CPU-offline processing for preemptible RCU.
*/
static void rcu_preempt_offline_cpu(int cpu)
{
rcu_preempt_qs(cpu);
return;
}
- if (per_cpu(rcu_preempt_data, cpu).qs_pending)
+ 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;
}
/*
- * Process callbacks for preemptable RCU.
+ * Process callbacks for preemptible RCU.
*/
static void rcu_preempt_process_callbacks(void)
{
&__get_cpu_var(rcu_preempt_data));
}
+#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 preemptable-RCU callback for invocation after a grace period.
+ * Queue a preemptible-RCU callback for invocation after a grace period.
*/
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
*/
void synchronize_rcu(void)
{
- struct rcu_synchronize rcu;
-
if (!rcu_scheduler_active)
return;
-
- init_rcu_head_on_stack(&rcu.head);
- init_completion(&rcu.completion);
- /* Will wake me after RCU finished. */
- call_rcu(&rcu.head, wakeme_after_rcu);
- /* Wait for it. */
- wait_for_completion(&rcu.completion);
- destroy_rcu_head_on_stack(&rcu.head);
+ wait_rcu_gp(call_rcu);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
raw_spin_lock_irqsave(&rnp->lock, flags);
for (;;) {
- if (!sync_rcu_preempt_exp_done(rnp))
+ 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);
wake_up(&sync_rcu_preempt_exp_wq);
break;
}
raw_spin_lock(&rnp->lock); /* irqs already disabled */
rnp->expmask &= ~mask;
}
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
/*
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(&rnp->lock); /* irqs already disabled */
- if (!list_empty(&rnp->blkd_tasks)) {
+ 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;
}
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
if (!must_wait)
rcu_report_exp_rnp(rsp, rnp);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
/*
- * Check to see if there is any immediate preemptable-RCU-related work
+ * Check to see if there is any immediate preemptible-RCU-related work
* to be done.
*/
static int rcu_preempt_pending(int cpu)
}
/*
- * Does preemptable RCU need the CPU to stay out of dynticks mode?
+ * Does preemptible RCU need the CPU to stay out of dynticks mode?
*/
static int rcu_preempt_needs_cpu(int cpu)
{
EXPORT_SYMBOL_GPL(rcu_barrier);
/*
- * Initialize preemptable RCU's per-CPU data.
+ * Initialize preemptible RCU's per-CPU data.
*/
static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
{
}
/*
- * Move preemptable RCU's callbacks from dying CPU to other online CPU.
+ * Move preemptible RCU's callbacks from dying CPU to other online CPU.
*/
static void rcu_preempt_send_cbs_to_online(void)
{
}
/*
- * Initialize preemptable RCU's state structures.
+ * Initialize preemptible RCU's state structures.
*/
static void __init __rcu_init_preempt(void)
{
}
/*
- * Check for a task exiting while in a preemptable-RCU read-side
+ * 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.
if (t->rcu_read_lock_nesting == 0)
return;
t->rcu_read_lock_nesting = 1;
- rcu_read_unlock();
+ __rcu_read_unlock();
}
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+static struct rcu_state *rcu_state = &rcu_sched_state;
+
/*
* Tell them what RCU they are running.
*/
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
- * Because preemptable RCU does not exist, we never have to check for
+ * 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 preemptable RCU does not exist, there are never any preempted
+ * Because preemptible RCU does not exist, there are never any preempted
* RCU readers.
*/
-static int rcu_preempted_readers(struct rcu_node *rnp)
+static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
{
return 0;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
- * Because preemptable RCU does not exist, we never have to check for
+ * 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 preemptable RCU does not exist, we never have to check for
+ * Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
static void rcu_print_task_stall(struct rcu_node *rnp)
}
/*
- * Because there is no preemptable RCU, there can be no readers blocked,
+ * 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.
*/
#ifdef CONFIG_HOTPLUG_CPU
/*
- * Because preemptable RCU does not exist, it never needs to migrate
+ * 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.
}
/*
- * Because preemptable RCU does not exist, it never needs CPU-offline
+ * Because preemptible RCU does not exist, it never needs CPU-offline
* processing.
*/
static void rcu_preempt_offline_cpu(int cpu)
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
- * Because preemptable RCU does not exist, it never has any callbacks
+ * Because preemptible RCU does not exist, it never has any callbacks
* to check.
*/
static void rcu_preempt_check_callbacks(int cpu)
}
/*
- * Because preemptable RCU does not exist, it never has any callbacks
+ * Because preemptible RCU does not exist, it never has any callbacks
* to process.
*/
static void rcu_preempt_process_callbacks(void)
/*
* Wait for an rcu-preempt grace period, but make it happen quickly.
- * But because preemptable RCU does not exist, map to rcu-sched.
+ * But because preemptible RCU does not exist, map to rcu-sched.
*/
void synchronize_rcu_expedited(void)
{
#ifdef CONFIG_HOTPLUG_CPU
/*
- * Because preemptable RCU does not exist, there is never any need to
+ * 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.
*/
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
- * Because preemptable RCU does not exist, it never has any work to do.
+ * Because preemptible RCU does not exist, it never has any work to do.
*/
static int rcu_preempt_pending(int cpu)
{
}
/*
- * Because preemptable RCU does not exist, it never needs any CPU.
+ * Because preemptible RCU does not exist, it never needs any CPU.
*/
static int rcu_preempt_needs_cpu(int cpu)
{
}
/*
- * Because preemptable RCU does not exist, rcu_barrier() is just
+ * Because preemptible RCU does not exist, rcu_barrier() is just
* another name for rcu_barrier_sched().
*/
void rcu_barrier(void)
EXPORT_SYMBOL_GPL(rcu_barrier);
/*
- * Because preemptable RCU does not exist, there is no per-CPU
+ * Because preemptible RCU does not exist, there is no per-CPU
* data to initialize.
*/
static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
}
/*
- * Because there is no preemptable RCU, there are no callbacks to move.
+ * Because there is no preemptible RCU, there are no callbacks to move.
*/
static void rcu_preempt_send_cbs_to_online(void)
{
}
/*
- * Because preemptable RCU does not exist, it need not be initialized.
+ * 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 */
+
+/*
+ * 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;
+ t->rcu_boosted = 1;
+ 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 rnp->exp_tasks != NULL || rnp->boost_tasks != NULL;
+}
+
+/*
+ * Timer handler to initiate waking up of boost kthreads that
+ * have yielded the CPU due to excessive numbers of tasks to
+ * boost. We wake up the per-rcu_node kthread, which in turn
+ * will wake up the booster kthread.
+ */
+static void rcu_boost_kthread_timer(unsigned long arg)
+{
+ invoke_rcu_node_kthread((struct rcu_node *)arg);
+}
+
+/*
+ * 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) {
+ trace_rcu_utilization("End boost kthread@rcu_yield");
+ rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp);
+ 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,
+ * but irqs remain disabled. 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 != NULL)
+ wake_up_process(t);
+ } 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))
+ wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
+ local_irq_restore(flags);
+}
+
+/*
+ * Set the affinity of the boost kthread. The CPU-hotplug locks are
+ * held, so no one should be messing with the existence of the boost
+ * kthread.
+ */
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
+ cpumask_var_t cm)
+{
+ struct task_struct *t;
+
+ t = rnp->boost_kthread_task;
+ if (t != NULL)
+ set_cpus_allowed_ptr(rnp->boost_kthread_task, cm);
+}
+
+#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)
+{
+ unsigned long flags;
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (&rcu_preempt_state != rsp)
+ 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_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
+ return 0;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Stop the RCU's per-CPU kthread when its CPU goes offline,.
+ */
+static void rcu_stop_cpu_kthread(int cpu)
+{
+ struct task_struct *t;
+
+ /* Stop the CPU's kthread. */
+ t = per_cpu(rcu_cpu_kthread_task, cpu);
+ if (t != NULL) {
+ per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
+ kthread_stop(t);
+ }
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+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();
+}
+
+/*
+ * Wake up the specified per-rcu_node-structure kthread.
+ * Because the per-rcu_node kthreads are immortal, we don't need
+ * to do anything to keep them alive.
+ */
+static void invoke_rcu_node_kthread(struct rcu_node *rnp)
+{
+ struct task_struct *t;
+
+ t = rnp->node_kthread_task;
+ if (t != NULL)
+ wake_up_process(t);
+}
+
+/*
+ * Set the specified CPU's kthread to run RT or not, as specified by
+ * the to_rt argument. The CPU-hotplug locks are held, so the task
+ * is not going away.
+ */
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
+{
+ int policy;
+ struct sched_param sp;
+ struct task_struct *t;
+
+ t = per_cpu(rcu_cpu_kthread_task, cpu);
+ if (t == NULL)
+ return;
+ if (to_rt) {
+ policy = SCHED_FIFO;
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ } else {
+ policy = SCHED_NORMAL;
+ sp.sched_priority = 0;
+ }
+ sched_setscheduler_nocheck(t, policy, &sp);
+}
+
+/*
+ * Timer handler to initiate the waking up of per-CPU kthreads that
+ * have yielded the CPU due to excess numbers of RCU callbacks.
+ * We wake up the per-rcu_node kthread, which in turn will wake up
+ * the booster kthread.
+ */
+static void rcu_cpu_kthread_timer(unsigned long arg)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
+ struct rcu_node *rnp = rdp->mynode;
+
+ atomic_or(rdp->grpmask, &rnp->wakemask);
+ invoke_rcu_node_kthread(rnp);
+}
+
+/*
+ * Drop to non-real-time priority and yield, but only after posting a
+ * timer that will cause us to regain our real-time priority if we
+ * remain preempted. Either way, we restore our real-time priority
+ * before returning.
+ */
+static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
+{
+ struct sched_param sp;
+ struct timer_list yield_timer;
+
+ setup_timer_on_stack(&yield_timer, f, arg);
+ mod_timer(&yield_timer, jiffies + 2);
+ sp.sched_priority = 0;
+ sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
+ set_user_nice(current, 19);
+ schedule();
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+ del_timer(&yield_timer);
+}
+
+/*
+ * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
+ * This can happen while the corresponding CPU is either coming online
+ * or going offline. We cannot wait until the CPU is fully online
+ * before starting the kthread, because the various notifier functions
+ * can wait for RCU grace periods. So we park rcu_cpu_kthread() until
+ * the corresponding CPU is online.
+ *
+ * Return 1 if the kthread needs to stop, 0 otherwise.
+ *
+ * Caller must disable bh. This function can momentarily enable it.
+ */
+static int rcu_cpu_kthread_should_stop(int cpu)
+{
+ while (cpu_is_offline(cpu) ||
+ !cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) ||
+ smp_processor_id() != cpu) {
+ if (kthread_should_stop())
+ return 1;
+ per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+ per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
+ local_bh_enable();
+ schedule_timeout_uninterruptible(1);
+ if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)))
+ set_cpus_allowed_ptr(current, cpumask_of(cpu));
+ local_bh_disable();
+ }
+ per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
+ return 0;
+}
+
+/*
+ * 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 int rcu_cpu_kthread(void *arg)
+{
+ int cpu = (int)(long)arg;
+ unsigned long flags;
+ int spincnt = 0;
+ unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
+ char work;
+ char *workp = &per_cpu(rcu_cpu_has_work, cpu);
+
+ trace_rcu_utilization("Start CPU kthread@init");
+ for (;;) {
+ *statusp = RCU_KTHREAD_WAITING;
+ trace_rcu_utilization("End CPU kthread@rcu_wait");
+ rcu_wait(*workp != 0 || kthread_should_stop());
+ trace_rcu_utilization("Start CPU kthread@rcu_wait");
+ local_bh_disable();
+ if (rcu_cpu_kthread_should_stop(cpu)) {
+ local_bh_enable();
+ break;
+ }
+ *statusp = RCU_KTHREAD_RUNNING;
+ per_cpu(rcu_cpu_kthread_loops, cpu)++;
+ local_irq_save(flags);
+ work = *workp;
+ *workp = 0;
+ local_irq_restore(flags);
+ if (work)
+ rcu_kthread_do_work();
+ local_bh_enable();
+ if (*workp != 0)
+ spincnt++;
+ else
+ spincnt = 0;
+ if (spincnt > 10) {
+ *statusp = RCU_KTHREAD_YIELDING;
+ trace_rcu_utilization("End CPU kthread@rcu_yield");
+ rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
+ trace_rcu_utilization("Start CPU kthread@rcu_yield");
+ spincnt = 0;
+ }
+ }
+ *statusp = RCU_KTHREAD_STOPPED;
+ trace_rcu_utilization("End CPU kthread@term");
+ return 0;
+}
+
+/*
+ * Spawn a per-CPU kthread, setting up affinity and priority.
+ * Because the CPU hotplug lock is held, no other CPU will be attempting
+ * to manipulate rcu_cpu_kthread_task. There might be another CPU
+ * attempting to access it during boot, but the locking in kthread_bind()
+ * will enforce sufficient ordering.
+ *
+ * Please note that we cannot simply refuse to wake up the per-CPU
+ * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
+ * which can result in softlockup complaints if the task ends up being
+ * idle for more than a couple of minutes.
+ *
+ * However, please note also that we cannot bind the per-CPU kthread to its
+ * CPU until that CPU is fully online. We also cannot wait until the
+ * CPU is fully online before we create its per-CPU kthread, as this would
+ * deadlock the system when CPU notifiers tried waiting for grace
+ * periods. So we bind the per-CPU kthread to its CPU only if the CPU
+ * is online. If its CPU is not yet fully online, then the code in
+ * rcu_cpu_kthread() will wait until it is fully online, and then do
+ * the binding.
+ */
+static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
+{
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (!rcu_scheduler_fully_active ||
+ per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
+ return 0;
+ t = kthread_create_on_node(rcu_cpu_kthread,
+ (void *)(long)cpu,
+ cpu_to_node(cpu),
+ "rcuc%d", cpu);
+ if (IS_ERR(t))
+ return PTR_ERR(t);
+ if (cpu_online(cpu))
+ kthread_bind(t, cpu);
+ per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
+ WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ per_cpu(rcu_cpu_kthread_task, cpu) = t;
+ wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
+ return 0;
+}
+
+/*
+ * Per-rcu_node kthread, which is in charge of waking up the per-CPU
+ * kthreads when needed. We ignore requests to wake up kthreads
+ * for offline CPUs, which is OK because force_quiescent_state()
+ * takes care of this case.
+ */
+static int rcu_node_kthread(void *arg)
+{
+ int cpu;
+ unsigned long flags;
+ unsigned long mask;
+ struct rcu_node *rnp = (struct rcu_node *)arg;
+ struct sched_param sp;
+ struct task_struct *t;
+
+ for (;;) {
+ rnp->node_kthread_status = RCU_KTHREAD_WAITING;
+ rcu_wait(atomic_read(&rnp->wakemask) != 0);
+ rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ mask = atomic_xchg(&rnp->wakemask, 0);
+ rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
+ if ((mask & 0x1) == 0)
+ continue;
+ preempt_disable();
+ t = per_cpu(rcu_cpu_kthread_task, cpu);
+ if (!cpu_online(cpu) || t == NULL) {
+ preempt_enable();
+ continue;
+ }
+ per_cpu(rcu_cpu_has_work, cpu) = 1;
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ preempt_enable();
+ }
+ }
+ /* NOTREACHED */
+ rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
+ return 0;
+}
+
+/*
+ * 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_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+ cpumask_var_t cm;
+ int cpu;
+ unsigned long mask = rnp->qsmaskinit;
+
+ if (rnp->node_kthread_task == NULL)
+ return;
+ if (!alloc_cpumask_var(&cm, GFP_KERNEL))
+ return;
+ cpumask_clear(cm);
+ 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(rnp->node_kthread_task, cm);
+ rcu_boost_kthread_setaffinity(rnp, cm);
+ free_cpumask_var(cm);
+}
+
+/*
+ * Spawn a per-rcu_node kthread, setting priority and affinity.
+ * Called during boot before online/offline can happen, or, if
+ * during runtime, with the main CPU-hotplug locks held. So only
+ * one of these can be executing at a time.
+ */
+static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
+ struct rcu_node *rnp)
+{
+ unsigned long flags;
+ int rnp_index = rnp - &rsp->node[0];
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (!rcu_scheduler_fully_active ||
+ rnp->qsmaskinit == 0)
+ return 0;
+ if (rnp->node_kthread_task == NULL) {
+ t = kthread_create(rcu_node_kthread, (void *)rnp,
+ "rcun%d", rnp_index);
+ if (IS_ERR(t))
+ return PTR_ERR(t);
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ rnp->node_kthread_task = t;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ sp.sched_priority = 99;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
+ }
+ return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
+}
+
+/*
+ * Spawn all kthreads -- called as soon as the scheduler is running.
+ */
+static int __init rcu_spawn_kthreads(void)
+{
+ int cpu;
+ struct rcu_node *rnp;
+
+ rcu_scheduler_fully_active = 1;
+ for_each_possible_cpu(cpu) {
+ per_cpu(rcu_cpu_has_work, cpu) = 0;
+ if (cpu_online(cpu))
+ (void)rcu_spawn_one_cpu_kthread(cpu);
+ }
+ rnp = rcu_get_root(rcu_state);
+ (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
+ if (NUM_RCU_NODES > 1) {
+ rcu_for_each_leaf_node(rcu_state, rnp)
+ (void)rcu_spawn_one_node_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_cpu_kthread(cpu);
+ if (rnp->node_kthread_task == NULL)
+ (void)rcu_spawn_one_node_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 void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
+{
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+static void rcu_stop_cpu_kthread(int cpu)
+{
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+}
+
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
+{
+}
+
+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 */
+
#ifndef CONFIG_SMP
void synchronize_sched_expedited(void)
*
* Because it is not legal to invoke rcu_process_callbacks() with irqs
* disabled, we do one pass of force_quiescent_state(), then do a
- * invoke_rcu_kthread() to cause rcu_process_callbacks() to be invoked later.
- * The per-cpu rcu_dyntick_drain variable controls the sequencing.
+ * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
+ * later. The per-cpu rcu_dyntick_drain variable controls the sequencing.
*/
int rcu_needs_cpu(int cpu)
{
/* If RCU callbacks are still pending, RCU still needs this CPU. */
if (c)
- invoke_rcu_kthread();
+ invoke_rcu_core();
return c;
}
Code Review / linux-2.6.git / blobdiff