linux/kernel/rcutree_plugin.h

2095 lines
62 KiB
C

/*
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
* Internal non-public definitions that provide either classic
* or preemptible semantics.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright Red Hat, 2009
* Copyright IBM Corporation, 2009
*
* Author: Ingo Molnar <mingo@elte.hu>
* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/
#include <linux/delay.h>
#include <linux/oom.h>
#include <linux/smpboot.h>
#define RCU_KTHREAD_PRIO 1
#ifdef CONFIG_RCU_BOOST
#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
#else
#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
#endif
/*
* Check the RCU kernel configuration parameters and print informative
* messages about anything out of the ordinary. If you like #ifdef, you
* will love this function.
*/
static void __init rcu_bootup_announce_oddness(void)
{
#ifdef CONFIG_RCU_TRACE
printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
printk(KERN_INFO
"\tRCU dyntick-idle grace-period acceleration is enabled.\n");
#endif
#ifdef CONFIG_PROVE_RCU
printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
#endif
#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
#endif
#if NUM_RCU_LVL_4 != 0
printk(KERN_INFO "\tFour-level hierarchy is enabled.\n");
#endif
if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
if (nr_cpu_ids != NR_CPUS)
printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
}
#ifdef CONFIG_TREE_PREEMPT_RCU
struct rcu_state rcu_preempt_state =
RCU_STATE_INITIALIZER(rcu_preempt, call_rcu);
DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
static struct rcu_state *rcu_state = &rcu_preempt_state;
static int rcu_preempted_readers_exp(struct rcu_node *rnp);
/*
* Tell them what RCU they are running.
*/
static void __init rcu_bootup_announce(void)
{
printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
/*
* Return the number of RCU-preempt batches processed thus far
* for debug and statistics.
*/
long rcu_batches_completed_preempt(void)
{
return rcu_preempt_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
/*
* Return the number of RCU batches processed thus far for debug & stats.
*/
long rcu_batches_completed(void)
{
return rcu_batches_completed_preempt();
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);
/*
* Force a quiescent state for preemptible RCU.
*/
void rcu_force_quiescent_state(void)
{
force_quiescent_state(&rcu_preempt_state);
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
* Record a preemptible-RCU quiescent state for the specified CPU. Note
* that this just means that the task currently running on the CPU is
* not in a quiescent state. There might be any number of tasks blocked
* while in an RCU read-side critical section.
*
* Unlike the other rcu_*_qs() functions, callers to this function
* must disable irqs in order to protect the assignment to
* ->rcu_read_unlock_special.
*/
static void rcu_preempt_qs(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
if (rdp->passed_quiesce == 0)
trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
rdp->passed_quiesce = 1;
current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
}
/*
* We have entered the scheduler, and the current task might soon be
* context-switched away from. If this task is in an RCU read-side
* critical section, we will no longer be able to rely on the CPU to
* record that fact, so we enqueue the task on the blkd_tasks list.
* The task will dequeue itself when it exits the outermost enclosing
* RCU read-side critical section. Therefore, the current grace period
* cannot be permitted to complete until the blkd_tasks list entries
* predating the current grace period drain, in other words, until
* rnp->gp_tasks becomes NULL.
*
* Caller must disable preemption.
*/
static void rcu_preempt_note_context_switch(int cpu)
{
struct task_struct *t = current;
unsigned long flags;
struct rcu_data *rdp;
struct rcu_node *rnp;
if (t->rcu_read_lock_nesting > 0 &&
(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
/* Possibly blocking in an RCU read-side critical section. */
rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave(&rnp->lock, flags);
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
t->rcu_blocked_node = rnp;
/*
* If this CPU has already checked in, then this task
* will hold up the next grace period rather than the
* current grace period. Queue the task accordingly.
* If the task is queued for the current grace period
* (i.e., this CPU has not yet passed through a quiescent
* state for the current grace period), then as long
* as that task remains queued, the current grace period
* cannot end. Note that there is some uncertainty as
* to exactly when the current grace period started.
* We take a conservative approach, which can result
* in unnecessarily waiting on tasks that started very
* slightly after the current grace period began. C'est
* la vie!!!
*
* But first, note that the current CPU must still be
* on line!
*/
WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
rnp->gp_tasks = &t->rcu_node_entry;
#ifdef CONFIG_RCU_BOOST
if (rnp->boost_tasks != NULL)
rnp->boost_tasks = rnp->gp_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
} else {
list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
if (rnp->qsmask & rdp->grpmask)
rnp->gp_tasks = &t->rcu_node_entry;
}
trace_rcu_preempt_task(rdp->rsp->name,
t->pid,
(rnp->qsmask & rdp->grpmask)
? rnp->gpnum
: rnp->gpnum + 1);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
} else if (t->rcu_read_lock_nesting < 0 &&
t->rcu_read_unlock_special) {
/*
* Complete exit from RCU read-side critical section on
* behalf of preempted instance of __rcu_read_unlock().
*/
rcu_read_unlock_special(t);
}
/*
* Either we were not in an RCU read-side critical section to
* begin with, or we have now recorded that critical section
* globally. Either way, we can now note a quiescent state
* for this CPU. Again, if we were in an RCU read-side critical
* section, and if that critical section was blocking the current
* grace period, then the fact that the task has been enqueued
* means that we continue to block the current grace period.
*/
local_irq_save(flags);
rcu_preempt_qs(cpu);
local_irq_restore(flags);
}
/*
* Check for preempted RCU readers blocking the current grace period
* for the specified rcu_node structure. If the caller needs a reliable
* answer, it must hold the rcu_node's ->lock.
*/
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
{
return rnp->gp_tasks != NULL;
}
/*
* Record a quiescent state for all tasks that were previously queued
* on the specified rcu_node structure and that were blocking the current
* RCU grace period. The caller must hold the specified rnp->lock with
* irqs disabled, and this lock is released upon return, but irqs remain
* disabled.
*/
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
__releases(rnp->lock)
{
unsigned long mask;
struct rcu_node *rnp_p;
if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return; /* Still need more quiescent states! */
}
rnp_p = rnp->parent;
if (rnp_p == NULL) {
/*
* Either there is only one rcu_node in the tree,
* or tasks were kicked up to root rcu_node due to
* CPUs going offline.
*/
rcu_report_qs_rsp(&rcu_preempt_state, flags);
return;
}
/* Report up the rest of the hierarchy. */
mask = rnp->grpmask;
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
}
/*
* Advance a ->blkd_tasks-list pointer to the next entry, instead
* returning NULL if at the end of the list.
*/
static struct list_head *rcu_next_node_entry(struct task_struct *t,
struct rcu_node *rnp)
{
struct list_head *np;
np = t->rcu_node_entry.next;
if (np == &rnp->blkd_tasks)
np = NULL;
return np;
}
/*
* Handle special cases during rcu_read_unlock(), such as needing to
* notify RCU core processing or task having blocked during the RCU
* read-side critical section.
*/
void rcu_read_unlock_special(struct task_struct *t)
{
int empty;
int empty_exp;
int empty_exp_now;
unsigned long flags;
struct list_head *np;
#ifdef CONFIG_RCU_BOOST
struct rt_mutex *rbmp = NULL;
#endif /* #ifdef CONFIG_RCU_BOOST */
struct rcu_node *rnp;
int special;
/* NMI handlers cannot block and cannot safely manipulate state. */
if (in_nmi())
return;
local_irq_save(flags);
/*
* If RCU core is waiting for this CPU to exit critical section,
* let it know that we have done so.
*/
special = t->rcu_read_unlock_special;
if (special & RCU_READ_UNLOCK_NEED_QS) {
rcu_preempt_qs(smp_processor_id());
}
/* Hardware IRQ handlers cannot block. */
if (in_irq() || in_serving_softirq()) {
local_irq_restore(flags);
return;
}
/* Clean up if blocked during RCU read-side critical section. */
if (special & RCU_READ_UNLOCK_BLOCKED) {
t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
/*
* Remove this task from the list it blocked on. The
* task can migrate while we acquire the lock, but at
* most one time. So at most two passes through loop.
*/
for (;;) {
rnp = t->rcu_blocked_node;
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
if (rnp == t->rcu_blocked_node)
break;
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
empty = !rcu_preempt_blocked_readers_cgp(rnp);
empty_exp = !rcu_preempted_readers_exp(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
np = rcu_next_node_entry(t, rnp);
list_del_init(&t->rcu_node_entry);
t->rcu_blocked_node = NULL;
trace_rcu_unlock_preempted_task("rcu_preempt",
rnp->gpnum, t->pid);
if (&t->rcu_node_entry == rnp->gp_tasks)
rnp->gp_tasks = np;
if (&t->rcu_node_entry == rnp->exp_tasks)
rnp->exp_tasks = np;
#ifdef CONFIG_RCU_BOOST
if (&t->rcu_node_entry == rnp->boost_tasks)
rnp->boost_tasks = np;
/* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
if (t->rcu_boost_mutex) {
rbmp = t->rcu_boost_mutex;
t->rcu_boost_mutex = NULL;
}
#endif /* #ifdef CONFIG_RCU_BOOST */
/*
* If this was the last task on the current list, and if
* we aren't waiting on any CPUs, report the quiescent state.
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
* so we must take a snapshot of the expedited state.
*/
empty_exp_now = !rcu_preempted_readers_exp(rnp);
if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
trace_rcu_quiescent_state_report("preempt_rcu",
rnp->gpnum,
0, rnp->qsmask,
rnp->level,
rnp->grplo,
rnp->grphi,
!!rnp->gp_tasks);
rcu_report_unblock_qs_rnp(rnp, flags);
} else {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
#ifdef CONFIG_RCU_BOOST
/* Unboost if we were boosted. */
if (rbmp)
rt_mutex_unlock(rbmp);
#endif /* #ifdef CONFIG_RCU_BOOST */
/*
* If this was the last task on the expedited lists,
* then we need to report up the rcu_node hierarchy.
*/
if (!empty_exp && empty_exp_now)
rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
} else {
local_irq_restore(flags);
}
}
#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
/*
* Dump detailed information for all tasks blocking the current RCU
* grace period on the specified rcu_node structure.
*/
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
unsigned long flags;
struct task_struct *t;
raw_spin_lock_irqsave(&rnp->lock, flags);
if (!rcu_preempt_blocked_readers_cgp(rnp)) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
t = list_entry(rnp->gp_tasks,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
sched_show_task(t);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
/*
* Dump detailed information for all tasks blocking the current RCU
* grace period.
*/
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
struct rcu_node *rnp = rcu_get_root(rsp);
rcu_print_detail_task_stall_rnp(rnp);
rcu_for_each_leaf_node(rsp, rnp)
rcu_print_detail_task_stall_rnp(rnp);
}
#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
#ifdef CONFIG_RCU_CPU_STALL_INFO
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
rnp->level, rnp->grplo, rnp->grphi);
}
static void rcu_print_task_stall_end(void)
{
printk(KERN_CONT "\n");
}
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
}
static void rcu_print_task_stall_end(void)
{
}
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each.
*/
static int rcu_print_task_stall(struct rcu_node *rnp)
{
struct task_struct *t;
int ndetected = 0;
if (!rcu_preempt_blocked_readers_cgp(rnp))
return 0;
rcu_print_task_stall_begin(rnp);
t = list_entry(rnp->gp_tasks,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
printk(KERN_CONT " P%d", t->pid);
ndetected++;
}
rcu_print_task_stall_end();
return ndetected;
}
/*
* Check that the list of blocked tasks for the newly completed grace
* period is in fact empty. It is a serious bug to complete a grace
* period that still has RCU readers blocked! This function must be
* invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
* must be held by the caller.
*
* Also, if there are blocked tasks on the list, they automatically
* block the newly created grace period, so set up ->gp_tasks accordingly.
*/
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
if (!list_empty(&rnp->blkd_tasks))
rnp->gp_tasks = rnp->blkd_tasks.next;
WARN_ON_ONCE(rnp->qsmask);
}
#ifdef CONFIG_HOTPLUG_CPU
/*
* Handle tasklist migration for case in which all CPUs covered by the
* specified rcu_node have gone offline. Move them up to the root
* rcu_node. The reason for not just moving them to the immediate
* parent is to remove the need for rcu_read_unlock_special() to
* make more than two attempts to acquire the target rcu_node's lock.
* Returns true if there were tasks blocking the current RCU grace
* period.
*
* Returns 1 if there was previously a task blocking the current grace
* period on the specified rcu_node structure.
*
* The caller must hold rnp->lock with irqs disabled.
*/
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
struct rcu_node *rnp,
struct rcu_data *rdp)
{
struct list_head *lp;
struct list_head *lp_root;
int retval = 0;
struct rcu_node *rnp_root = rcu_get_root(rsp);
struct task_struct *t;
if (rnp == rnp_root) {
WARN_ONCE(1, "Last CPU thought to be offlined?");
return 0; /* Shouldn't happen: at least one CPU online. */
}
/* If we are on an internal node, complain bitterly. */
WARN_ON_ONCE(rnp != rdp->mynode);
/*
* Move tasks up to root rcu_node. Don't try to get fancy for
* this corner-case operation -- just put this node's tasks
* at the head of the root node's list, and update the root node's
* ->gp_tasks and ->exp_tasks pointers to those of this node's,
* if non-NULL. This might result in waiting for more tasks than
* absolutely necessary, but this is a good performance/complexity
* tradeoff.
*/
if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
retval |= RCU_OFL_TASKS_NORM_GP;
if (rcu_preempted_readers_exp(rnp))
retval |= RCU_OFL_TASKS_EXP_GP;
lp = &rnp->blkd_tasks;
lp_root = &rnp_root->blkd_tasks;
while (!list_empty(lp)) {
t = list_entry(lp->next, typeof(*t), rcu_node_entry);
raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
list_del(&t->rcu_node_entry);
t->rcu_blocked_node = rnp_root;
list_add(&t->rcu_node_entry, lp_root);
if (&t->rcu_node_entry == rnp->gp_tasks)
rnp_root->gp_tasks = rnp->gp_tasks;
if (&t->rcu_node_entry == rnp->exp_tasks)
rnp_root->exp_tasks = rnp->exp_tasks;
#ifdef CONFIG_RCU_BOOST
if (&t->rcu_node_entry == rnp->boost_tasks)
rnp_root->boost_tasks = rnp->boost_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
}
rnp->gp_tasks = NULL;
rnp->exp_tasks = NULL;
#ifdef CONFIG_RCU_BOOST
rnp->boost_tasks = NULL;
/*
* In case root is being boosted and leaf was not. Make sure
* that we boost the tasks blocking the current grace period
* in this case.
*/
raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
if (rnp_root->boost_tasks != NULL &&
rnp_root->boost_tasks != rnp_root->gp_tasks &&
rnp_root->boost_tasks != rnp_root->exp_tasks)
rnp_root->boost_tasks = rnp_root->gp_tasks;
raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
#endif /* #ifdef CONFIG_RCU_BOOST */
return retval;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Check for a quiescent state from the current CPU. When a task blocks,
* the task is recorded in the corresponding CPU's rcu_node structure,
* which is checked elsewhere.
*
* Caller must disable hard irqs.
*/
static void rcu_preempt_check_callbacks(int cpu)
{
struct task_struct *t = current;
if (t->rcu_read_lock_nesting == 0) {
rcu_preempt_qs(cpu);
return;
}
if (t->rcu_read_lock_nesting > 0 &&
per_cpu(rcu_preempt_data, cpu).qs_pending)
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
}
#ifdef CONFIG_RCU_BOOST
static void rcu_preempt_do_callbacks(void)
{
rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
}
#endif /* #ifdef CONFIG_RCU_BOOST */
/*
* Queue a preemptible-RCU callback for invocation after a grace period.
*/
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_preempt_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu);
/*
* Queue an RCU callback for lazy invocation after a grace period.
* This will likely be later named something like "call_rcu_lazy()",
* but this change will require some way of tagging the lazy RCU
* callbacks in the list of pending callbacks. Until then, this
* function may only be called from __kfree_rcu().
*/
void kfree_call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_preempt_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);
/**
* synchronize_rcu - wait until a grace period has elapsed.
*
* Control will return to the caller some time after a full grace
* period has elapsed, in other words after all currently executing RCU
* read-side critical sections have completed. Note, however, that
* upon return from synchronize_rcu(), the caller might well be executing
* concurrently with new RCU read-side critical sections that began while
* synchronize_rcu() was waiting. RCU read-side critical sections are
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
*/
void synchronize_rcu(void)
{
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
!lock_is_held(&rcu_lock_map) &&
!lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu() in RCU read-side critical section");
if (!rcu_scheduler_active)
return;
wait_rcu_gp(call_rcu);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
static unsigned long sync_rcu_preempt_exp_count;
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
/*
* Return non-zero if there are any tasks in RCU read-side critical
* sections blocking the current preemptible-RCU expedited grace period.
* If there is no preemptible-RCU expedited grace period currently in
* progress, returns zero unconditionally.
*/
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
{
return rnp->exp_tasks != NULL;
}
/*
* return non-zero if there is no RCU expedited grace period in progress
* for the specified rcu_node structure, in other words, if all CPUs and
* tasks covered by the specified rcu_node structure have done their bit
* for the current expedited grace period. Works only for preemptible
* RCU -- other RCU implementation use other means.
*
* Caller must hold sync_rcu_preempt_exp_mutex.
*/
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
{
return !rcu_preempted_readers_exp(rnp) &&
ACCESS_ONCE(rnp->expmask) == 0;
}
/*
* Report the exit from RCU read-side critical section for the last task
* that queued itself during or before the current expedited preemptible-RCU
* grace period. This event is reported either to the rcu_node structure on
* which the task was queued or to one of that rcu_node structure's ancestors,
* recursively up the tree. (Calm down, calm down, we do the recursion
* iteratively!)
*
* Most callers will set the "wake" flag, but the task initiating the
* expedited grace period need not wake itself.
*
* Caller must hold sync_rcu_preempt_exp_mutex.
*/
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
bool wake)
{
unsigned long flags;
unsigned long mask;
raw_spin_lock_irqsave(&rnp->lock, flags);
for (;;) {
if (!sync_rcu_preempt_exp_done(rnp)) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
break;
}
if (rnp->parent == NULL) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (wake)
wake_up(&sync_rcu_preempt_exp_wq);
break;
}
mask = rnp->grpmask;
raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
rnp = rnp->parent;
raw_spin_lock(&rnp->lock); /* irqs already disabled */
rnp->expmask &= ~mask;
}
}
/*
* Snapshot the tasks blocking the newly started preemptible-RCU expedited
* grace period for the specified rcu_node structure. If there are no such
* tasks, report it up the rcu_node hierarchy.
*
* Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
*/
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
unsigned long flags;
int must_wait = 0;
raw_spin_lock_irqsave(&rnp->lock, flags);
if (list_empty(&rnp->blkd_tasks)) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
} else {
rnp->exp_tasks = rnp->blkd_tasks.next;
rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
must_wait = 1;
}
if (!must_wait)
rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
}
/**
* synchronize_rcu_expedited - Brute-force RCU grace period
*
* Wait for an RCU-preempt grace period, but expedite it. The basic
* idea is to invoke synchronize_sched_expedited() to push all the tasks to
* the ->blkd_tasks lists and wait for this list to drain. This consumes
* significant time on all CPUs and is unfriendly to real-time workloads,
* so is thus not recommended for any sort of common-case code.
* In fact, if you are using synchronize_rcu_expedited() in a loop,
* please restructure your code to batch your updates, and then Use a
* single synchronize_rcu() instead.
*
* Note that it is illegal to call this function while holding any lock
* that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
* to call this function from a CPU-hotplug notifier. Failing to observe
* these restriction will result in deadlock.
*/
void synchronize_rcu_expedited(void)
{
unsigned long flags;
struct rcu_node *rnp;
struct rcu_state *rsp = &rcu_preempt_state;
unsigned long snap;
int trycount = 0;
smp_mb(); /* Caller's modifications seen first by other CPUs. */
snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
smp_mb(); /* Above access cannot bleed into critical section. */
/*
* Block CPU-hotplug operations. This means that any CPU-hotplug
* operation that finds an rcu_node structure with tasks in the
* process of being boosted will know that all tasks blocking
* this expedited grace period will already be in the process of
* being boosted. This simplifies the process of moving tasks
* from leaf to root rcu_node structures.
*/
get_online_cpus();
/*
* Acquire lock, falling back to synchronize_rcu() if too many
* lock-acquisition failures. Of course, if someone does the
* expedited grace period for us, just leave.
*/
while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
if (ULONG_CMP_LT(snap,
ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
put_online_cpus();
goto mb_ret; /* Others did our work for us. */
}
if (trycount++ < 10) {
udelay(trycount * num_online_cpus());
} else {
put_online_cpus();
synchronize_rcu();
return;
}
}
if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
put_online_cpus();
goto unlock_mb_ret; /* Others did our work for us. */
}
/* force all RCU readers onto ->blkd_tasks lists. */
synchronize_sched_expedited();
/* Initialize ->expmask for all non-leaf rcu_node structures. */
rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->expmask = rnp->qsmaskinit;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
/* Snapshot current state of ->blkd_tasks lists. */
rcu_for_each_leaf_node(rsp, rnp)
sync_rcu_preempt_exp_init(rsp, rnp);
if (NUM_RCU_NODES > 1)
sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
put_online_cpus();
/* Wait for snapshotted ->blkd_tasks lists to drain. */
rnp = rcu_get_root(rsp);
wait_event(sync_rcu_preempt_exp_wq,
sync_rcu_preempt_exp_done(rnp));
/* Clean up and exit. */
smp_mb(); /* ensure expedited GP seen before counter increment. */
ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
unlock_mb_ret:
mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
smp_mb(); /* ensure subsequent action seen after grace period. */
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
/**
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
*/
void rcu_barrier(void)
{
_rcu_barrier(&rcu_preempt_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier);
/*
* Initialize preemptible RCU's state structures.
*/
static void __init __rcu_init_preempt(void)
{
rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
}
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
static struct rcu_state *rcu_state = &rcu_sched_state;
/*
* Tell them what RCU they are running.
*/
static void __init rcu_bootup_announce(void)
{
printk(KERN_INFO "Hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
/*
* Return the number of RCU batches processed thus far for debug & stats.
*/
long rcu_batches_completed(void)
{
return rcu_batches_completed_sched();
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);
/*
* Force a quiescent state for RCU, which, because there is no preemptible
* RCU, becomes the same as rcu-sched.
*/
void rcu_force_quiescent_state(void)
{
rcu_sched_force_quiescent_state();
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
* Because preemptible RCU does not exist, we never have to check for
* CPUs being in quiescent states.
*/
static void rcu_preempt_note_context_switch(int cpu)
{
}
/*
* Because preemptible RCU does not exist, there are never any preempted
* RCU readers.
*/
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
{
return 0;
}
#ifdef CONFIG_HOTPLUG_CPU
/* Because preemptible RCU does not exist, no quieting of tasks. */
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
{
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
static int rcu_print_task_stall(struct rcu_node *rnp)
{
return 0;
}
/*
* Because there is no preemptible RCU, there can be no readers blocked,
* so there is no need to check for blocked tasks. So check only for
* bogus qsmask values.
*/
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
WARN_ON_ONCE(rnp->qsmask);
}
#ifdef CONFIG_HOTPLUG_CPU
/*
* Because preemptible RCU does not exist, it never needs to migrate
* tasks that were blocked within RCU read-side critical sections, and
* such non-existent tasks cannot possibly have been blocking the current
* grace period.
*/
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
struct rcu_node *rnp,
struct rcu_data *rdp)
{
return 0;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Because preemptible RCU does not exist, it never has any callbacks
* to check.
*/
static void rcu_preempt_check_callbacks(int cpu)
{
}
/*
* Queue an RCU callback for lazy invocation after a grace period.
* This will likely be later named something like "call_rcu_lazy()",
* but this change will require some way of tagging the lazy RCU
* callbacks in the list of pending callbacks. Until then, this
* function may only be called from __kfree_rcu().
*
* Because there is no preemptible RCU, we use RCU-sched instead.
*/
void kfree_call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_sched_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);
/*
* Wait for an rcu-preempt grace period, but make it happen quickly.
* But because preemptible RCU does not exist, map to rcu-sched.
*/
void synchronize_rcu_expedited(void)
{
synchronize_sched_expedited();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
#ifdef CONFIG_HOTPLUG_CPU
/*
* Because preemptible RCU does not exist, there is never any need to
* report on tasks preempted in RCU read-side critical sections during
* expedited RCU grace periods.
*/
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
bool wake)
{
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Because preemptible RCU does not exist, rcu_barrier() is just
* another name for rcu_barrier_sched().
*/
void rcu_barrier(void)
{
rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);
/*
* Because preemptible RCU does not exist, it need not be initialized.
*/
static void __init __rcu_init_preempt(void)
{
}
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
#ifdef CONFIG_RCU_BOOST
#include "rtmutex_common.h"
#ifdef CONFIG_RCU_TRACE
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
if (list_empty(&rnp->blkd_tasks))
rnp->n_balk_blkd_tasks++;
else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
rnp->n_balk_exp_gp_tasks++;
else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
rnp->n_balk_boost_tasks++;
else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
rnp->n_balk_notblocked++;
else if (rnp->gp_tasks != NULL &&
ULONG_CMP_LT(jiffies, rnp->boost_time))
rnp->n_balk_notyet++;
else
rnp->n_balk_nos++;
}
#else /* #ifdef CONFIG_RCU_TRACE */
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
}
#endif /* #else #ifdef CONFIG_RCU_TRACE */
static void rcu_wake_cond(struct task_struct *t, int status)
{
/*
* If the thread is yielding, only wake it when this
* is invoked from idle
*/
if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
wake_up_process(t);
}
/*
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
* or ->boost_tasks, advancing the pointer to the next task in the
* ->blkd_tasks list.
*
* Note that irqs must be enabled: boosting the task can block.
* Returns 1 if there are more tasks needing to be boosted.
*/
static int rcu_boost(struct rcu_node *rnp)
{
unsigned long flags;
struct rt_mutex mtx;
struct task_struct *t;
struct list_head *tb;
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
return 0; /* Nothing left to boost. */
raw_spin_lock_irqsave(&rnp->lock, flags);
/*
* Recheck under the lock: all tasks in need of boosting
* might exit their RCU read-side critical sections on their own.
*/
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return 0;
}
/*
* Preferentially boost tasks blocking expedited grace periods.
* This cannot starve the normal grace periods because a second
* expedited grace period must boost all blocked tasks, including
* those blocking the pre-existing normal grace period.
*/
if (rnp->exp_tasks != NULL) {
tb = rnp->exp_tasks;
rnp->n_exp_boosts++;
} else {
tb = rnp->boost_tasks;
rnp->n_normal_boosts++;
}
rnp->n_tasks_boosted++;
/*
* We boost task t by manufacturing an rt_mutex that appears to
* be held by task t. We leave a pointer to that rt_mutex where
* task t can find it, and task t will release the mutex when it
* exits its outermost RCU read-side critical section. Then
* simply acquiring this artificial rt_mutex will boost task
* t's priority. (Thanks to tglx for suggesting this approach!)
*
* Note that task t must acquire rnp->lock to remove itself from
* the ->blkd_tasks list, which it will do from exit() if from
* nowhere else. We therefore are guaranteed that task t will
* stay around at least until we drop rnp->lock. Note that
* rnp->lock also resolves races between our priority boosting
* and task t's exiting its outermost RCU read-side critical
* section.
*/
t = container_of(tb, struct task_struct, rcu_node_entry);
rt_mutex_init_proxy_locked(&mtx, t);
t->rcu_boost_mutex = &mtx;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
ACCESS_ONCE(rnp->boost_tasks) != NULL;
}
/*
* Priority-boosting kthread. One per leaf rcu_node and one for the
* root rcu_node.
*/
static int rcu_boost_kthread(void *arg)
{
struct rcu_node *rnp = (struct rcu_node *)arg;
int spincnt = 0;
int more2boost;
trace_rcu_utilization("Start boost kthread@init");
for (;;) {
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
trace_rcu_utilization("End boost kthread@rcu_wait");
rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
trace_rcu_utilization("Start boost kthread@rcu_wait");
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
more2boost = rcu_boost(rnp);
if (more2boost)
spincnt++;
else
spincnt = 0;
if (spincnt > 10) {
rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
trace_rcu_utilization("End boost kthread@rcu_yield");
schedule_timeout_interruptible(2);
trace_rcu_utilization("Start boost kthread@rcu_yield");
spincnt = 0;
}
}
/* NOTREACHED */
trace_rcu_utilization("End boost kthread@notreached");
return 0;
}
/*
* Check to see if it is time to start boosting RCU readers that are
* blocking the current grace period, and, if so, tell the per-rcu_node
* kthread to start boosting them. If there is an expedited grace
* period in progress, it is always time to boost.
*
* The caller must hold rnp->lock, which this function releases.
* The ->boost_kthread_task is immortal, so we don't need to worry
* about it going away.
*/
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
{
struct task_struct *t;
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
rnp->n_balk_exp_gp_tasks++;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
if (rnp->exp_tasks != NULL ||
(rnp->gp_tasks != NULL &&
rnp->boost_tasks == NULL &&
rnp->qsmask == 0 &&
ULONG_CMP_GE(jiffies, rnp->boost_time))) {
if (rnp->exp_tasks == NULL)
rnp->boost_tasks = rnp->gp_tasks;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
t = rnp->boost_kthread_task;
if (t)
rcu_wake_cond(t, rnp->boost_kthread_status);
} else {
rcu_initiate_boost_trace(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
}
/*
* Wake up the per-CPU kthread to invoke RCU callbacks.
*/
static void invoke_rcu_callbacks_kthread(void)
{
unsigned long flags;
local_irq_save(flags);
__this_cpu_write(rcu_cpu_has_work, 1);
if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
current != __this_cpu_read(rcu_cpu_kthread_task)) {
rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
__this_cpu_read(rcu_cpu_kthread_status));
}
local_irq_restore(flags);
}
/*
* Is the current CPU running the RCU-callbacks kthread?
* Caller must have preemption disabled.
*/
static bool rcu_is_callbacks_kthread(void)
{
return __get_cpu_var(rcu_cpu_kthread_task) == current;
}
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
/*
* Do priority-boost accounting for the start of a new grace period.
*/
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
}
/*
* Create an RCU-boost kthread for the specified node if one does not
* already exist. We only create this kthread for preemptible RCU.
* Returns zero if all is well, a negated errno otherwise.
*/
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
struct rcu_node *rnp)
{
int rnp_index = rnp - &rsp->node[0];
unsigned long flags;
struct sched_param sp;
struct task_struct *t;
if (&rcu_preempt_state != rsp)
return 0;
if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
return 0;
rsp->boost = 1;
if (rnp->boost_kthread_task != NULL)
return 0;
t = kthread_create(rcu_boost_kthread, (void *)rnp,
"rcub/%d", rnp_index);
if (IS_ERR(t))
return PTR_ERR(t);
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->boost_kthread_task = t;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
sp.sched_priority = RCU_BOOST_PRIO;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
return 0;
}
static void rcu_kthread_do_work(void)
{
rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
rcu_preempt_do_callbacks();
}
static void rcu_cpu_kthread_setup(unsigned int cpu)
{
struct sched_param sp;
sp.sched_priority = RCU_KTHREAD_PRIO;
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
}
static void rcu_cpu_kthread_park(unsigned int cpu)
{
per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
}
static int rcu_cpu_kthread_should_run(unsigned int cpu)
{
return __get_cpu_var(rcu_cpu_has_work);
}
/*
* Per-CPU kernel thread that invokes RCU callbacks. This replaces the
* RCU softirq used in flavors and configurations of RCU that do not
* support RCU priority boosting.
*/
static void rcu_cpu_kthread(unsigned int cpu)
{
unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status);
char work, *workp = &__get_cpu_var(rcu_cpu_has_work);
int spincnt;
for (spincnt = 0; spincnt < 10; spincnt++) {
trace_rcu_utilization("Start CPU kthread@rcu_wait");
local_bh_disable();
*statusp = RCU_KTHREAD_RUNNING;
this_cpu_inc(rcu_cpu_kthread_loops);
local_irq_disable();
work = *workp;
*workp = 0;
local_irq_enable();
if (work)
rcu_kthread_do_work();
local_bh_enable();
if (*workp == 0) {
trace_rcu_utilization("End CPU kthread@rcu_wait");
*statusp = RCU_KTHREAD_WAITING;
return;
}
}
*statusp = RCU_KTHREAD_YIELDING;
trace_rcu_utilization("Start CPU kthread@rcu_yield");
schedule_timeout_interruptible(2);
trace_rcu_utilization("End CPU kthread@rcu_yield");
*statusp = RCU_KTHREAD_WAITING;
}
/*
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
* served by the rcu_node in question. The CPU hotplug lock is still
* held, so the value of rnp->qsmaskinit will be stable.
*
* We don't include outgoingcpu in the affinity set, use -1 if there is
* no outgoing CPU. If there are no CPUs left in the affinity set,
* this function allows the kthread to execute on any CPU.
*/
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
struct task_struct *t = rnp->boost_kthread_task;
unsigned long mask = rnp->qsmaskinit;
cpumask_var_t cm;
int cpu;
if (!t)
return;
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
return;
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
if ((mask & 0x1) && cpu != outgoingcpu)
cpumask_set_cpu(cpu, cm);
if (cpumask_weight(cm) == 0) {
cpumask_setall(cm);
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
cpumask_clear_cpu(cpu, cm);
WARN_ON_ONCE(cpumask_weight(cm) == 0);
}
set_cpus_allowed_ptr(t, cm);
free_cpumask_var(cm);
}
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
.store = &rcu_cpu_kthread_task,
.thread_should_run = rcu_cpu_kthread_should_run,
.thread_fn = rcu_cpu_kthread,
.thread_comm = "rcuc/%u",
.setup = rcu_cpu_kthread_setup,
.park = rcu_cpu_kthread_park,
};
/*
* Spawn all kthreads -- called as soon as the scheduler is running.
*/
static int __init rcu_spawn_kthreads(void)
{
struct rcu_node *rnp;
int cpu;
rcu_scheduler_fully_active = 1;
for_each_possible_cpu(cpu)
per_cpu(rcu_cpu_has_work, cpu) = 0;
BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
rnp = rcu_get_root(rcu_state);
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
if (NUM_RCU_NODES > 1) {
rcu_for_each_leaf_node(rcu_state, rnp)
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
}
return 0;
}
early_initcall(rcu_spawn_kthreads);
static void __cpuinit rcu_prepare_kthreads(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
struct rcu_node *rnp = rdp->mynode;
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
if (rcu_scheduler_fully_active)
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
}
#else /* #ifdef CONFIG_RCU_BOOST */
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
{
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
static void invoke_rcu_callbacks_kthread(void)
{
WARN_ON_ONCE(1);
}
static bool rcu_is_callbacks_kthread(void)
{
return false;
}
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
}
static int __init rcu_scheduler_really_started(void)
{
rcu_scheduler_fully_active = 1;
return 0;
}
early_initcall(rcu_scheduler_really_started);
static void __cpuinit rcu_prepare_kthreads(int cpu)
{
}
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#if !defined(CONFIG_RCU_FAST_NO_HZ)
/*
* Check to see if any future RCU-related work will need to be done
* by the current CPU, even if none need be done immediately, returning
* 1 if so. This function is part of the RCU implementation; it is -not-
* an exported member of the RCU API.
*
* Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
* any flavor of RCU.
*/
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
{
*delta_jiffies = ULONG_MAX;
return rcu_cpu_has_callbacks(cpu);
}
/*
* Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
*/
static void rcu_prepare_for_idle_init(int cpu)
{
}
/*
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
* after it.
*/
static void rcu_cleanup_after_idle(int cpu)
{
}
/*
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
* is nothing.
*/
static void rcu_prepare_for_idle(int cpu)
{
}
/*
* Don't bother keeping a running count of the number of RCU callbacks
* posted because CONFIG_RCU_FAST_NO_HZ=n.
*/
static void rcu_idle_count_callbacks_posted(void)
{
}
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
/*
* This code is invoked when a CPU goes idle, at which point we want
* to have the CPU do everything required for RCU so that it can enter
* the energy-efficient dyntick-idle mode. This is handled by a
* state machine implemented by rcu_prepare_for_idle() below.
*
* The following three proprocessor symbols control this state machine:
*
* RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt
* to satisfy RCU. Beyond this point, it is better to incur a periodic
* scheduling-clock interrupt than to loop through the state machine
* at full power.
* RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are
* optional if RCU does not need anything immediately from this
* CPU, even if this CPU still has RCU callbacks queued. The first
* times through the state machine are mandatory: we need to give
* the state machine a chance to communicate a quiescent state
* to the RCU core.
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
* to sleep in dyntick-idle mode with RCU callbacks pending. This
* is sized to be roughly one RCU grace period. Those energy-efficiency
* benchmarkers who might otherwise be tempted to set this to a large
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
* system. And if you are -that- concerned about energy efficiency,
* just power the system down and be done with it!
* RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
* permitted to sleep in dyntick-idle mode with only lazy RCU
* callbacks pending. Setting this too high can OOM your system.
*
* The values below work well in practice. If future workloads require
* adjustment, they can be converted into kernel config parameters, though
* making the state machine smarter might be a better option.
*/
#define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */
#define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
extern int tick_nohz_enabled;
/*
* Does the specified flavor of RCU have non-lazy callbacks pending on
* the specified CPU? Both RCU flavor and CPU are specified by the
* rcu_data structure.
*/
static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
{
return rdp->qlen != rdp->qlen_lazy;
}
#ifdef CONFIG_TREE_PREEMPT_RCU
/*
* Are there non-lazy RCU-preempt callbacks? (There cannot be if there
* is no RCU-preempt in the kernel.)
*/
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
return __rcu_cpu_has_nonlazy_callbacks(rdp);
}
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
return 0;
}
#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
/*
* Does any flavor of RCU have non-lazy callbacks on the specified CPU?
*/
static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
{
return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
__rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
}
/*
* Allow the CPU to enter dyntick-idle mode if either: (1) There are no
* callbacks on this CPU, (2) this CPU has not yet attempted to enter
* dyntick-idle mode, or (3) this CPU is in the process of attempting to
* enter dyntick-idle mode. Otherwise, if we have recently tried and failed
* to enter dyntick-idle mode, we refuse to try to enter it. After all,
* it is better to incur scheduling-clock interrupts than to spin
* continuously for the same time duration!
*
* The delta_jiffies argument is used to store the time when RCU is
* going to need the CPU again if it still has callbacks. The reason
* for this is that rcu_prepare_for_idle() might need to post a timer,
* but if so, it will do so after tick_nohz_stop_sched_tick() has set
* the wakeup time for this CPU. This means that RCU's timer can be
* delayed until the wakeup time, which defeats the purpose of posting
* a timer.
*/
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
{
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
/* Flag a new idle sojourn to the idle-entry state machine. */
rdtp->idle_first_pass = 1;
/* If no callbacks, RCU doesn't need the CPU. */
if (!rcu_cpu_has_callbacks(cpu)) {
*delta_jiffies = ULONG_MAX;
return 0;
}
if (rdtp->dyntick_holdoff == jiffies) {
/* RCU recently tried and failed, so don't try again. */
*delta_jiffies = 1;
return 1;
}
/* Set up for the possibility that RCU will post a timer. */
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
*delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies,
RCU_IDLE_GP_DELAY) - jiffies;
} else {
*delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY;
*delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;
}
return 0;
}
/*
* Handler for smp_call_function_single(). The only point of this
* handler is to wake the CPU up, so the handler does only tracing.
*/
void rcu_idle_demigrate(void *unused)
{
trace_rcu_prep_idle("Demigrate");
}
/*
* Timer handler used to force CPU to start pushing its remaining RCU
* callbacks in the case where it entered dyntick-idle mode with callbacks
* pending. The hander doesn't really need to do anything because the
* real work is done upon re-entry to idle, or by the next scheduling-clock
* interrupt should idle not be re-entered.
*
* One special case: the timer gets migrated without awakening the CPU
* on which the timer was scheduled on. In this case, we must wake up
* that CPU. We do so with smp_call_function_single().
*/
static void rcu_idle_gp_timer_func(unsigned long cpu_in)
{
int cpu = (int)cpu_in;
trace_rcu_prep_idle("Timer");
if (cpu != smp_processor_id())
smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0);
else
WARN_ON_ONCE(1); /* Getting here can hang the system... */
}
/*
* Initialize the timer used to pull CPUs out of dyntick-idle mode.
*/
static void rcu_prepare_for_idle_init(int cpu)
{
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
rdtp->dyntick_holdoff = jiffies - 1;
setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu);
rdtp->idle_gp_timer_expires = jiffies - 1;
rdtp->idle_first_pass = 1;
}
/*
* Clean up for exit from idle. Because we are exiting from idle, there
* is no longer any point to ->idle_gp_timer, so cancel it. This will
* do nothing if this timer is not active, so just cancel it unconditionally.
*/
static void rcu_cleanup_after_idle(int cpu)
{
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
del_timer(&rdtp->idle_gp_timer);
trace_rcu_prep_idle("Cleanup after idle");
rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled);
}
/*
* Check to see if any RCU-related work can be done by the current CPU,
* and if so, schedule a softirq to get it done. This function is part
* of the RCU implementation; it is -not- an exported member of the RCU API.
*
* The idea is for the current CPU to clear out all work required by the
* RCU core for the current grace period, so that this CPU can be permitted
* to enter dyntick-idle mode. In some cases, it will need to be awakened
* at the end of the grace period by whatever CPU ends the grace period.
* This allows CPUs to go dyntick-idle more quickly, and to reduce the
* number of wakeups by a modest integer factor.
*
* 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 ->dyntick_drain field controls the sequencing.
*
* The caller must have disabled interrupts.
*/
static void rcu_prepare_for_idle(int cpu)
{
struct timer_list *tp;
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
int tne;
/* Handle nohz enablement switches conservatively. */
tne = ACCESS_ONCE(tick_nohz_enabled);
if (tne != rdtp->tick_nohz_enabled_snap) {
if (rcu_cpu_has_callbacks(cpu))
invoke_rcu_core(); /* force nohz to see update. */
rdtp->tick_nohz_enabled_snap = tne;
return;
}
if (!tne)
return;
/* Adaptive-tick mode, where usermode execution is idle to RCU. */
if (!is_idle_task(current)) {
rdtp->dyntick_holdoff = jiffies - 1;
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
trace_rcu_prep_idle("User dyntick with callbacks");
rdtp->idle_gp_timer_expires =
round_up(jiffies + RCU_IDLE_GP_DELAY,
RCU_IDLE_GP_DELAY);
} else if (rcu_cpu_has_callbacks(cpu)) {
rdtp->idle_gp_timer_expires =
round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
trace_rcu_prep_idle("User dyntick with lazy callbacks");
} else {
return;
}
tp = &rdtp->idle_gp_timer;
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
return;
}
/*
* If this is an idle re-entry, for example, due to use of
* RCU_NONIDLE() or the new idle-loop tracing API within the idle
* loop, then don't take any state-machine actions, unless the
* momentary exit from idle queued additional non-lazy callbacks.
* Instead, repost the ->idle_gp_timer if this CPU has callbacks
* pending.
*/
if (!rdtp->idle_first_pass &&
(rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) {
if (rcu_cpu_has_callbacks(cpu)) {
tp = &rdtp->idle_gp_timer;
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
}
return;
}
rdtp->idle_first_pass = 0;
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1;
/*
* If there are no callbacks on this CPU, enter dyntick-idle mode.
* Also reset state to avoid prejudicing later attempts.
*/
if (!rcu_cpu_has_callbacks(cpu)) {
rdtp->dyntick_holdoff = jiffies - 1;
rdtp->dyntick_drain = 0;
trace_rcu_prep_idle("No callbacks");
return;
}
/*
* If in holdoff mode, just return. We will presumably have
* refrained from disabling the scheduling-clock tick.
*/
if (rdtp->dyntick_holdoff == jiffies) {
trace_rcu_prep_idle("In holdoff");
return;
}
/* Check and update the ->dyntick_drain sequencing. */
if (rdtp->dyntick_drain <= 0) {
/* First time through, initialize the counter. */
rdtp->dyntick_drain = RCU_IDLE_FLUSHES;
} else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&
!rcu_pending(cpu) &&
!local_softirq_pending()) {
/* Can we go dyntick-idle despite still having callbacks? */
rdtp->dyntick_drain = 0;
rdtp->dyntick_holdoff = jiffies;
if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
trace_rcu_prep_idle("Dyntick with callbacks");
rdtp->idle_gp_timer_expires =
round_up(jiffies + RCU_IDLE_GP_DELAY,
RCU_IDLE_GP_DELAY);
} else {
rdtp->idle_gp_timer_expires =
round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
trace_rcu_prep_idle("Dyntick with lazy callbacks");
}
tp = &rdtp->idle_gp_timer;
mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
return; /* Nothing more to do immediately. */
} else if (--(rdtp->dyntick_drain) <= 0) {
/* We have hit the limit, so time to give up. */
rdtp->dyntick_holdoff = jiffies;
trace_rcu_prep_idle("Begin holdoff");
invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */
return;
}
/*
* Do one step of pushing the remaining RCU callbacks through
* the RCU core state machine.
*/
#ifdef CONFIG_TREE_PREEMPT_RCU
if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
rcu_preempt_qs(cpu);
force_quiescent_state(&rcu_preempt_state);
}
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
if (per_cpu(rcu_sched_data, cpu).nxtlist) {
rcu_sched_qs(cpu);
force_quiescent_state(&rcu_sched_state);
}
if (per_cpu(rcu_bh_data, cpu).nxtlist) {
rcu_bh_qs(cpu);
force_quiescent_state(&rcu_bh_state);
}
/*
* If RCU callbacks are still pending, RCU still needs this CPU.
* So try forcing the callbacks through the grace period.
*/
if (rcu_cpu_has_callbacks(cpu)) {
trace_rcu_prep_idle("More callbacks");
invoke_rcu_core();
} else {
trace_rcu_prep_idle("Callbacks drained");
}
}
/*
* Keep a running count of the number of non-lazy callbacks posted
* on this CPU. This running counter (which is never decremented) allows
* rcu_prepare_for_idle() to detect when something out of the idle loop
* posts a callback, even if an equal number of callbacks are invoked.
* Of course, callbacks should only be posted from within a trace event
* designed to be called from idle or from within RCU_NONIDLE().
*/
static void rcu_idle_count_callbacks_posted(void)
{
__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
}
/*
* Data for flushing lazy RCU callbacks at OOM time.
*/
static atomic_t oom_callback_count;
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
/*
* RCU OOM callback -- decrement the outstanding count and deliver the
* wake-up if we are the last one.
*/
static void rcu_oom_callback(struct rcu_head *rhp)
{
if (atomic_dec_and_test(&oom_callback_count))
wake_up(&oom_callback_wq);
}
/*
* Post an rcu_oom_notify callback on the current CPU if it has at
* least one lazy callback. This will unnecessarily post callbacks
* to CPUs that already have a non-lazy callback at the end of their
* callback list, but this is an infrequent operation, so accept some
* extra overhead to keep things simple.
*/
static void rcu_oom_notify_cpu(void *unused)
{
struct rcu_state *rsp;
struct rcu_data *rdp;
for_each_rcu_flavor(rsp) {
rdp = __this_cpu_ptr(rsp->rda);
if (rdp->qlen_lazy != 0) {
atomic_inc(&oom_callback_count);
rsp->call(&rdp->oom_head, rcu_oom_callback);
}
}
}
/*
* If low on memory, ensure that each CPU has a non-lazy callback.
* This will wake up CPUs that have only lazy callbacks, in turn
* ensuring that they free up the corresponding memory in a timely manner.
* Because an uncertain amount of memory will be freed in some uncertain
* timeframe, we do not claim to have freed anything.
*/
static int rcu_oom_notify(struct notifier_block *self,
unsigned long notused, void *nfreed)
{
int cpu;
/* Wait for callbacks from earlier instance to complete. */
wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
/*
* Prevent premature wakeup: ensure that all increments happen
* before there is a chance of the counter reaching zero.
*/
atomic_set(&oom_callback_count, 1);
get_online_cpus();
for_each_online_cpu(cpu) {
smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
cond_resched();
}
put_online_cpus();
/* Unconditionally decrement: no need to wake ourselves up. */
atomic_dec(&oom_callback_count);
return NOTIFY_OK;
}
static struct notifier_block rcu_oom_nb = {
.notifier_call = rcu_oom_notify
};
static int __init rcu_register_oom_notifier(void)
{
register_oom_notifier(&rcu_oom_nb);
return 0;
}
early_initcall(rcu_register_oom_notifier);
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
#ifdef CONFIG_RCU_CPU_STALL_INFO
#ifdef CONFIG_RCU_FAST_NO_HZ
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
struct timer_list *tltp = &rdtp->idle_gp_timer;
char c;
c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.';
if (timer_pending(tltp))
sprintf(cp, "drain=%d %c timer=%lu",
rdtp->dyntick_drain, c, tltp->expires - jiffies);
else
sprintf(cp, "drain=%d %c timer not pending",
rdtp->dyntick_drain, c);
}
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
*cp = '\0';
}
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
printk(KERN_CONT "\n");
}
/*
* Print out diagnostic information for the specified stalled CPU.
*
* If the specified CPU is aware of the current RCU grace period
* (flavor specified by rsp), then print the number of scheduling
* clock interrupts the CPU has taken during the time that it has
* been aware. Otherwise, print the number of RCU grace periods
* that this CPU is ignorant of, for example, "1" if the CPU was
* aware of the previous grace period.
*
* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
*/
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
char fast_no_hz[72];
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_dynticks *rdtp = rdp->dynticks;
char *ticks_title;
unsigned long ticks_value;
if (rsp->gpnum == rdp->gpnum) {
ticks_title = "ticks this GP";
ticks_value = rdp->ticks_this_gp;
} else {
ticks_title = "GPs behind";
ticks_value = rsp->gpnum - rdp->gpnum;
}
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
cpu, ticks_value, ticks_title,
atomic_read(&rdtp->dynticks) & 0xfff,
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
fast_no_hz);
}
/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
printk(KERN_ERR "\t");
}
/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
rdp->ticks_this_gp = 0;
}
/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
struct rcu_state *rsp;
for_each_rcu_flavor(rsp)
__this_cpu_ptr(rsp->rda)->ticks_this_gp++;
}
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
static void print_cpu_stall_info_begin(void)
{
printk(KERN_CONT " {");
}
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
printk(KERN_CONT " %d", cpu);
}
static void print_cpu_stall_info_end(void)
{
printk(KERN_CONT "} ");
}
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
}
static void increment_cpu_stall_ticks(void)
{
}
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */