/*
* 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
*/
#include <linux/delay.h>
+#include <linux/stop_machine.h>
+
+/*
+ * 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 "\tVerbose stalled-CPUs detection is disabled.\n");
+#endif
+#if NUM_RCU_LVL_4 != 0
+ printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n");
+#endif
+}
#ifdef CONFIG_TREE_PREEMPT_RCU
struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
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
- "Experimental 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.
+ *
+ * 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);
+
rdp->passed_quiesc_completed = rdp->gpnum - 1;
barrier();
rdp->passed_quiesc = 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 appropriate entry
- * of the blocked_tasks[] array. 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 blocked_tasks[] entry indexed by the low-order bit of
- * rnp->gpnum empties.
+ * 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.
*/
{
struct task_struct *t = current;
unsigned long flags;
- int phase;
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. */
- rdp = rcu_preempt_state.rda[cpu];
+ 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;
* (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.
+ * 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));
- phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1;
- list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);
+ 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;
+ }
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);
}
/*
* grace period, then the fact that the task has been enqueued
* means that we continue to block the current grace period.
*/
- rcu_preempt_qs(cpu);
local_irq_save(flags);
- t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
+ rcu_preempt_qs(cpu);
local_irq_restore(flags);
}
/*
- * 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.
*/
void __rcu_read_lock(void)
{
- ACCESS_ONCE(current->rcu_read_lock_nesting)++;
+ current->rcu_read_lock_nesting++;
barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);
* 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)
{
- int phase = rnp->gpnum & 0x1;
-
- return !list_empty(&rnp->blocked_tasks[phase]) ||
- !list_empty(&rnp->blocked_tasks[phase + 2]);
+ 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! */
}
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.
*/
-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;
unsigned long flags;
+ struct list_head *np;
struct rcu_node *rnp;
int special;
*/
special = t->rcu_read_unlock_special;
if (special & RCU_READ_UNLOCK_NEED_QS) {
- t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
rcu_preempt_qs(smp_processor_id());
}
/* 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);
+ 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;
/*
else
rcu_report_unblock_qs_rnp(rnp, 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,
* then we need to report up the rcu_node hierarchy.
}
/*
- * 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 */
- if (--ACCESS_ONCE(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);
-#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+#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;
+
+ if (!rcu_preempt_blocked_readers_cgp(rnp))
+ return;
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ 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 */
/*
* Scan the current list of tasks blocked within RCU read-side critical
*/
static void rcu_print_task_stall(struct rcu_node *rnp)
{
- unsigned long flags;
- struct list_head *lp;
- int phase;
struct task_struct *t;
- if (rcu_preempted_readers(rnp)) {
- raw_spin_lock_irqsave(&rnp->lock, flags);
- phase = rnp->gpnum & 0x1;
- lp = &rnp->blocked_tasks[phase];
- list_for_each_entry(t, lp, rcu_node_entry)
- printk(" P%d", t->pid);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- }
+ if (!rcu_preempt_blocked_readers_cgp(rnp))
+ 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)
+ printk(" P%d", t->pid);
}
-#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+/*
+ * Suppress preemptible RCU's CPU stall warnings by pushing the
+ * time of the next stall-warning message comfortably far into the
+ * future.
+ */
+static void rcu_preempt_stall_reset(void)
+{
+ rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+}
/*
* Check that the list of blocked tasks for the newly completed 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_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);
}
struct rcu_node *rnp,
struct rcu_data *rdp)
{
- int i;
struct list_head *lp;
struct list_head *lp_root;
int retval = 0;
struct rcu_node *rnp_root = rcu_get_root(rsp);
- struct task_struct *tp;
+ 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. */
}
- WARN_ON_ONCE(rnp != rdp->mynode &&
- (!list_empty(&rnp->blocked_tasks[0]) ||
- !list_empty(&rnp->blocked_tasks[1]) ||
- !list_empty(&rnp->blocked_tasks[2]) ||
- !list_empty(&rnp->blocked_tasks[3])));
+
+ /* If we are on an internal node, complain bitterly. */
+ WARN_ON_ONCE(rnp != rdp->mynode);
/*
- * Move tasks up to root rcu_node. Rely on the fact that the
- * root rcu_node can be at most one ahead of the rest of the
- * rcu_nodes in terms of gp_num value. This fact allows us to
- * move the blocked_tasks[] array directly, element by element.
+ * 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_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;
- for (i = 0; i < 4; i++) {
- lp = &rnp->blocked_tasks[i];
- lp_root = &rnp_root->blocked_tasks[i];
- while (!list_empty(lp)) {
- tp = list_entry(lp->next, typeof(*tp), rcu_node_entry);
- raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
- list_del(&tp->rcu_node_entry);
- tp->rcu_blocked_node = rnp_root;
- list_add(&tp->rcu_node_entry, lp_root);
- raw_spin_unlock(&rnp_root->lock); /* irqs remain disabled */
- }
+ 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 */
}
+
+#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)
{
struct task_struct *t = current;
if (t->rcu_read_lock_nesting == 0) {
- t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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))
{
*
* 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. RCU read-side critical
- * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
- * and may be nested.
+ * 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.
*/
void synchronize_rcu(void)
{
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);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
*/
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
{
- return !list_empty(&rnp->blocked_tasks[2]) ||
- !list_empty(&rnp->blocked_tasks[3]);
+ return rnp->exp_tasks != NULL;
}
/*
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)
{
- int must_wait;
+ unsigned long flags;
+ int must_wait = 0;
- raw_spin_lock(&rnp->lock); /* irqs already disabled */
- list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]);
- list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]);
- must_wait = rcu_preempted_readers_exp(rnp);
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
+ 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);
}
/*
* 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 ->blocked_tasks[] lists, move all entries from the first set of
- * ->blocked_tasks[] lists to the second set, and finally wait for this
- * second set to drain.
+ * the ->blkd_tasks lists and wait for this list to drain.
*/
void synchronize_rcu_expedited(void)
{
if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
goto unlock_mb_ret; /* Others did our work for us. */
- /* force all RCU readers onto blocked_tasks[]. */
+ /* force all RCU readers onto ->blkd_tasks lists. */
synchronize_sched_expedited();
raw_spin_lock_irqsave(&rsp->onofflock, flags);
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
- /* Snapshot current state of ->blocked_tasks[] lists. */
+ /* 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)
raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
- /* Wait for snapshotted ->blocked_tasks[] lists to drain. */
+ /* 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));
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 to ->orphan_cbs_list.
+ * Move preemptible RCU's callbacks from dying CPU to other online CPU.
*/
-static void rcu_preempt_send_cbs_to_orphanage(void)
+static void rcu_preempt_send_cbs_to_online(void)
{
- rcu_send_cbs_to_orphanage(&rcu_preempt_state);
+ rcu_send_cbs_to_online(&rcu_preempt_state);
}
/*
- * Initialize preemptable RCU's state structures.
+ * Initialize preemptible RCU's state structures.
*/
static void __init __rcu_init_preempt(void)
{
- RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);
+ rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
}
/*
- * 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.
*/
static void __init rcu_bootup_announce(void)
{
printk(KERN_INFO "Hierarchical RCU implementation.\n");
+ rcu_bootup_announce_oddness();
}
/*
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 */
-#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+/*
+ * 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)
{
}
-#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+/*
+ * Because preemptible RCU does not exist, there is no need to suppress
+ * its CPU stall warnings.
+ */
+static void rcu_preempt_stall_reset(void)
+{
+}
/*
- * 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)
{
}
-/*
- * In classic RCU, call_rcu() is just call_rcu_sched().
- */
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
-{
- call_rcu_sched(head, func);
-}
-EXPORT_SYMBOL_GPL(call_rcu);
-
/*
* 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_orphanage(void)
+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;
+
+ for (;;) {
+ rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
+ rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
+ rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
+ more2boost = rcu_boost(rnp);
+ if (more2boost)
+ spincnt++;
+ else
+ spincnt = 0;
+ if (spincnt > 10) {
+ rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp);
+ spincnt = 0;
+ }
+ }
+ /* 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) {
+ local_irq_restore(flags);
+ return;
+ }
+ 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
+ * earlier RCU softirq.
+ */
+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);
+
+ for (;;) {
+ *statusp = RCU_KTHREAD_WAITING;
+ rcu_wait(*workp != 0 || kthread_should_stop());
+ 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;
+ rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
+ spincnt = 0;
+ }
+ }
+ *statusp = RCU_KTHREAD_STOPPED;
+ 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(rcu_cpu_kthread, (void *)(long)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)
+{
+ cond_resched();
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+#else /* #ifndef CONFIG_SMP */
+
+static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
+static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
+
+static int synchronize_sched_expedited_cpu_stop(void *data)
+{
+ /*
+ * There must be a full memory barrier on each affected CPU
+ * between the time that try_stop_cpus() is called and the
+ * time that it returns.
+ *
+ * In the current initial implementation of cpu_stop, the
+ * above condition is already met when the control reaches
+ * this point and the following smp_mb() is not strictly
+ * necessary. Do smp_mb() anyway for documentation and
+ * robustness against future implementation changes.
+ */
+ smp_mb(); /* See above comment block. */
+ return 0;
+}
+
+/*
+ * Wait for an rcu-sched grace period to elapse, but use "big hammer"
+ * approach to force grace period to end quickly. This consumes
+ * significant time on all CPUs, and is thus not recommended for
+ * any sort of common-case code.
+ *
+ * Note that it is illegal to call this function while holding any
+ * lock that is acquired by a CPU-hotplug notifier. Failing to
+ * observe this restriction will result in deadlock.
+ *
+ * This implementation can be thought of as an application of ticket
+ * locking to RCU, with sync_sched_expedited_started and
+ * sync_sched_expedited_done taking on the roles of the halves
+ * of the ticket-lock word. Each task atomically increments
+ * sync_sched_expedited_started upon entry, snapshotting the old value,
+ * then attempts to stop all the CPUs. If this succeeds, then each
+ * CPU will have executed a context switch, resulting in an RCU-sched
+ * grace period. We are then done, so we use atomic_cmpxchg() to
+ * update sync_sched_expedited_done to match our snapshot -- but
+ * only if someone else has not already advanced past our snapshot.
+ *
+ * On the other hand, if try_stop_cpus() fails, we check the value
+ * of sync_sched_expedited_done. If it has advanced past our
+ * initial snapshot, then someone else must have forced a grace period
+ * some time after we took our snapshot. In this case, our work is
+ * done for us, and we can simply return. Otherwise, we try again,
+ * but keep our initial snapshot for purposes of checking for someone
+ * doing our work for us.
+ *
+ * If we fail too many times in a row, we fall back to synchronize_sched().
+ */
+void synchronize_sched_expedited(void)
+{
+ int firstsnap, s, snap, trycount = 0;
+
+ /* Note that atomic_inc_return() implies full memory barrier. */
+ firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
+ get_online_cpus();
+
+ /*
+ * Each pass through the following loop attempts to force a
+ * context switch on each CPU.
+ */
+ while (try_stop_cpus(cpu_online_mask,
+ synchronize_sched_expedited_cpu_stop,
+ NULL) == -EAGAIN) {
+ put_online_cpus();
+
+ /* No joy, try again later. Or just synchronize_sched(). */
+ if (trycount++ < 10)
+ udelay(trycount * num_online_cpus());
+ else {
+ synchronize_sched();
+ return;
+ }
+
+ /* Check to see if someone else did our work for us. */
+ s = atomic_read(&sync_sched_expedited_done);
+ if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
+ smp_mb(); /* ensure test happens before caller kfree */
+ return;
+ }
+
+ /*
+ * Refetching sync_sched_expedited_started allows later
+ * callers to piggyback on our grace period. We subtract
+ * 1 to get the same token that the last incrementer got.
+ * We retry after they started, so our grace period works
+ * for them, and they started after our first try, so their
+ * grace period works for us.
+ */
+ get_online_cpus();
+ snap = atomic_read(&sync_sched_expedited_started) - 1;
+ smp_mb(); /* ensure read is before try_stop_cpus(). */
+ }
+
+ /*
+ * Everyone up to our most recent fetch is covered by our grace
+ * period. Update the counter, but only if our work is still
+ * relevant -- which it won't be if someone who started later
+ * than we did beat us to the punch.
+ */
+ do {
+ s = atomic_read(&sync_sched_expedited_done);
+ if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
+ smp_mb(); /* ensure test happens before caller kfree */
+ break;
+ }
+ } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
+
+ put_online_cpus();
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+#endif /* #else #ifndef CONFIG_SMP */
+
#if !defined(CONFIG_RCU_FAST_NO_HZ)
/*
return rcu_needs_cpu_quick_check(cpu);
}
+/*
+ * Check to see if we need to continue a callback-flush operations to
+ * allow the last CPU to enter dyntick-idle mode. But fast dyntick-idle
+ * entry is not configured, so we never do need to.
+ */
+static void rcu_needs_cpu_flush(void)
+{
+}
+
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
#define RCU_NEEDS_CPU_FLUSHES 5
+static DEFINE_PER_CPU(int, rcu_dyntick_drain);
+static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
/*
* Check to see if any future RCU-related work will need to be done
* only if all other CPUs are already in dynticks-idle mode. This will
* allow the CPU cores to be powered down immediately, as opposed to after
* waiting many milliseconds for grace periods to elapse.
+ *
+ * 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_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)
{
- int c = 1;
- int i;
+ int c = 0;
+ int snap;
int thatcpu;
+ /* Check for being in the holdoff period. */
+ if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies)
+ return rcu_needs_cpu_quick_check(cpu);
+
/* Don't bother unless we are the last non-dyntick-idle CPU. */
- for_each_cpu_not(thatcpu, nohz_cpu_mask)
- if (thatcpu != cpu)
+ for_each_online_cpu(thatcpu) {
+ if (thatcpu == cpu)
+ continue;
+ snap = atomic_add_return(0, &per_cpu(rcu_dynticks,
+ thatcpu).dynticks);
+ smp_mb(); /* Order sampling of snap with end of grace period. */
+ if ((snap & 0x1) != 0) {
+ per_cpu(rcu_dyntick_drain, cpu) = 0;
+ per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
return rcu_needs_cpu_quick_check(cpu);
-
- /* Try to push remaining RCU-sched and RCU-bh callbacks through. */
- for (i = 0; i < RCU_NEEDS_CPU_FLUSHES && c; i++) {
- c = 0;
- if (per_cpu(rcu_sched_data, cpu).nxtlist) {
- rcu_sched_qs(cpu);
- force_quiescent_state(&rcu_sched_state, 0);
- __rcu_process_callbacks(&rcu_sched_state,
- &per_cpu(rcu_sched_data, cpu));
- c = !!per_cpu(rcu_sched_data, cpu).nxtlist;
- }
- if (per_cpu(rcu_bh_data, cpu).nxtlist) {
- rcu_bh_qs(cpu);
- force_quiescent_state(&rcu_bh_state, 0);
- __rcu_process_callbacks(&rcu_bh_state,
- &per_cpu(rcu_bh_data, cpu));
- c = !!per_cpu(rcu_bh_data, cpu).nxtlist;
}
}
+ /* Check and update the rcu_dyntick_drain sequencing. */
+ if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {
+ /* First time through, initialize the counter. */
+ per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES;
+ } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
+ /* We have hit the limit, so time to give up. */
+ per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
+ return rcu_needs_cpu_quick_check(cpu);
+ }
+
+ /* Do one step pushing remaining RCU callbacks through. */
+ if (per_cpu(rcu_sched_data, cpu).nxtlist) {
+ rcu_sched_qs(cpu);
+ force_quiescent_state(&rcu_sched_state, 0);
+ c = c || per_cpu(rcu_sched_data, cpu).nxtlist;
+ }
+ if (per_cpu(rcu_bh_data, cpu).nxtlist) {
+ rcu_bh_qs(cpu);
+ force_quiescent_state(&rcu_bh_state, 0);
+ c = c || per_cpu(rcu_bh_data, cpu).nxtlist;
+ }
+
/* If RCU callbacks are still pending, RCU still needs this CPU. */
+ if (c)
+ invoke_rcu_core();
return c;
}
+/*
+ * Check to see if we need to continue a callback-flush operations to
+ * allow the last CPU to enter dyntick-idle mode.
+ */
+static void rcu_needs_cpu_flush(void)
+{
+ int cpu = smp_processor_id();
+ unsigned long flags;
+
+ if (per_cpu(rcu_dyntick_drain, cpu) <= 0)
+ return;
+ local_irq_save(flags);
+ (void)rcu_needs_cpu(cpu);
+ local_irq_restore(flags);
+}
+
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
Code Review / linux-2.6.git / blobdiff