blob: 9467a8b7e756173bc9a94cc5b9828066a9f50e16 [file] [log] [blame]
/*
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
* Internal non-public definitions that provide either classic
* or preemptible semantics.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, you can access it online at
* http://www.gnu.org/licenses/gpl-2.0.html.
*
* Copyright Red Hat, 2009
* Copyright IBM Corporation, 2009
*
* Author: Ingo Molnar <mingo@elte.hu>
* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/
#include <linux/delay.h>
#include <linux/gfp.h>
#include <linux/oom.h>
#include <linux/smpboot.h>
#include "../time/tick-internal.h"
#ifdef CONFIG_RCU_BOOST
#include "../locking/rtmutex_common.h"
/*
* Control variables for per-CPU and per-rcu_node kthreads. These
* handle all flavors of RCU.
*/
static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
DEFINE_PER_CPU(char, rcu_cpu_has_work);
#else /* #ifdef CONFIG_RCU_BOOST */
/*
* Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
* all uses are in dead code. Provide a definition to keep the compiler
* happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
* This probably needs to be excluded from -rt builds.
*/
#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifdef CONFIG_RCU_NOCB_CPU
static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
/*
* Check the RCU kernel configuration parameters and print informative
* messages about anything out of the ordinary.
*/
static void __init rcu_bootup_announce_oddness(void)
{
if (IS_ENABLED(CONFIG_RCU_TRACE))
pr_info("\tRCU debugfs-based tracing is enabled.\n");
if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
(!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
RCU_FANOUT);
if (rcu_fanout_exact)
pr_info("\tHierarchical RCU autobalancing is disabled.\n");
if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
if (IS_ENABLED(CONFIG_PROVE_RCU))
pr_info("\tRCU lockdep checking is enabled.\n");
if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE))
pr_info("\tRCU torture testing starts during boot.\n");
if (RCU_NUM_LVLS >= 4)
pr_info("\tFour(or more)-level hierarchy is enabled.\n");
if (RCU_FANOUT_LEAF != 16)
pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
RCU_FANOUT_LEAF);
if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
if (nr_cpu_ids != NR_CPUS)
pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
if (IS_ENABLED(CONFIG_RCU_BOOST))
pr_info("\tRCU kthread priority: %d.\n", kthread_prio);
}
#ifdef CONFIG_PREEMPT_RCU
RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
static struct rcu_state *const rcu_state_p = &rcu_preempt_state;
static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
bool wake);
/*
* Tell them what RCU they are running.
*/
static void __init rcu_bootup_announce(void)
{
pr_info("Preemptible hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
/* Flags for rcu_preempt_ctxt_queue() decision table. */
#define RCU_GP_TASKS 0x8
#define RCU_EXP_TASKS 0x4
#define RCU_GP_BLKD 0x2
#define RCU_EXP_BLKD 0x1
/*
* Queues a task preempted within an RCU-preempt read-side critical
* section into the appropriate location within the ->blkd_tasks list,
* depending on the states of any ongoing normal and expedited grace
* periods. The ->gp_tasks pointer indicates which element the normal
* grace period is waiting on (NULL if none), and the ->exp_tasks pointer
* indicates which element the expedited grace period is waiting on (again,
* NULL if none). If a grace period is waiting on a given element in the
* ->blkd_tasks list, it also waits on all subsequent elements. Thus,
* adding a task to the tail of the list blocks any grace period that is
* already waiting on one of the elements. In contrast, adding a task
* to the head of the list won't block any grace period that is already
* waiting on one of the elements.
*
* This queuing is imprecise, and can sometimes make an ongoing grace
* period wait for a task that is not strictly speaking blocking it.
* Given the choice, we needlessly block a normal grace period rather than
* blocking an expedited grace period.
*
* Note that an endless sequence of expedited grace periods still cannot
* indefinitely postpone a normal grace period. Eventually, all of the
* fixed number of preempted tasks blocking the normal grace period that are
* not also blocking the expedited grace period will resume and complete
* their RCU read-side critical sections. At that point, the ->gp_tasks
* pointer will equal the ->exp_tasks pointer, at which point the end of
* the corresponding expedited grace period will also be the end of the
* normal grace period.
*/
static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
__releases(rnp->lock) /* But leaves rrupts disabled. */
{
int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
(rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
(rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
(rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
struct task_struct *t = current;
/*
* Decide where to queue the newly blocked task. In theory,
* this could be an if-statement. In practice, when I tried
* that, it was quite messy.
*/
switch (blkd_state) {
case 0:
case RCU_EXP_TASKS:
case RCU_EXP_TASKS + RCU_GP_BLKD:
case RCU_GP_TASKS:
case RCU_GP_TASKS + RCU_EXP_TASKS:
/*
* Blocking neither GP, or first task blocking the normal
* GP but not blocking the already-waiting expedited GP.
* Queue at the head of the list to avoid unnecessarily
* blocking the already-waiting GPs.
*/
list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
break;
case RCU_EXP_BLKD:
case RCU_GP_BLKD:
case RCU_GP_BLKD + RCU_EXP_BLKD:
case RCU_GP_TASKS + RCU_EXP_BLKD:
case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
/*
* First task arriving that blocks either GP, or first task
* arriving that blocks the expedited GP (with the normal
* GP already waiting), or a task arriving that blocks
* both GPs with both GPs already waiting. Queue at the
* tail of the list to avoid any GP waiting on any of the
* already queued tasks that are not blocking it.
*/
list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
break;
case RCU_EXP_TASKS + RCU_EXP_BLKD:
case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
/*
* Second or subsequent task blocking the expedited GP.
* The task either does not block the normal GP, or is the
* first task blocking the normal GP. Queue just after
* the first task blocking the expedited GP.
*/
list_add(&t->rcu_node_entry, rnp->exp_tasks);
break;
case RCU_GP_TASKS + RCU_GP_BLKD:
case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
/*
* Second or subsequent task blocking the normal GP.
* The task does not block the expedited GP. Queue just
* after the first task blocking the normal GP.
*/
list_add(&t->rcu_node_entry, rnp->gp_tasks);
break;
default:
/* Yet another exercise in excessive paranoia. */
WARN_ON_ONCE(1);
break;
}
/*
* We have now queued the task. If it was the first one to
* block either grace period, update the ->gp_tasks and/or
* ->exp_tasks pointers, respectively, to reference the newly
* blocked tasks.
*/
if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
rnp->gp_tasks = &t->rcu_node_entry;
if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
rnp->exp_tasks = &t->rcu_node_entry;
raw_spin_unlock(&rnp->lock); /* rrupts remain disabled. */
/*
* Report the quiescent state for the expedited GP. This expedited
* GP should not be able to end until we report, so there should be
* no need to check for a subsequent expedited GP. (Though we are
* still in a quiescent state in any case.)
*/
if (blkd_state & RCU_EXP_BLKD &&
t->rcu_read_unlock_special.b.exp_need_qs) {
t->rcu_read_unlock_special.b.exp_need_qs = false;
rcu_report_exp_rdp(rdp->rsp, rdp, true);
} else {
WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
}
}
/*
* Record a preemptible-RCU quiescent state for the specified CPU. Note
* that this 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.
*
* As with the other rcu_*_qs() functions, callers to this function
* must disable preemption.
*/
static void rcu_preempt_qs(void)
{
if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
trace_rcu_grace_period(TPS("rcu_preempt"),
__this_cpu_read(rcu_data_p->gpnum),
TPS("cpuqs"));
__this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);
barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
current->rcu_read_unlock_special.b.need_qs = false;
}
}
/*
* We have entered the scheduler, and the current task might soon be
* context-switched away from. If this task is in an RCU read-side
* critical section, we will no longer be able to rely on the CPU to
* record that fact, so we enqueue the task on the blkd_tasks list.
* The task will dequeue itself when it exits the outermost enclosing
* RCU read-side critical section. Therefore, the current grace period
* cannot be permitted to complete until the blkd_tasks list entries
* predating the current grace period drain, in other words, until
* rnp->gp_tasks becomes NULL.
*
* Caller must disable interrupts.
*/
static void rcu_preempt_note_context_switch(void)
{
struct task_struct *t = current;
struct rcu_data *rdp;
struct rcu_node *rnp;
if (t->rcu_read_lock_nesting > 0 &&
!t->rcu_read_unlock_special.b.blocked) {
/* Possibly blocking in an RCU read-side critical section. */
rdp = this_cpu_ptr(rcu_state_p->rda);
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp);
t->rcu_read_unlock_special.b.blocked = true;
t->rcu_blocked_node = rnp;
/*
* Verify the CPU's sanity, trace the preemption, and
* then queue the task as required based on the states
* of any ongoing and expedited grace periods.
*/
WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
trace_rcu_preempt_task(rdp->rsp->name,
t->pid,
(rnp->qsmask & rdp->grpmask)
? rnp->gpnum
: rnp->gpnum + 1);
rcu_preempt_ctxt_queue(rnp, rdp);
} else if (t->rcu_read_lock_nesting < 0 &&
t->rcu_read_unlock_special.s) {
/*
* Complete exit from RCU read-side critical section on
* behalf of preempted instance of __rcu_read_unlock().
*/
rcu_read_unlock_special(t);
}
/*
* Either we were not in an RCU read-side critical section to
* begin with, or we have now recorded that critical section
* globally. Either way, we can now note a quiescent state
* for this CPU. Again, if we were in an RCU read-side critical
* section, and if that critical section was blocking the current
* grace period, then the fact that the task has been enqueued
* means that we continue to block the current grace period.
*/
rcu_preempt_qs();
}
/*
* Check for preempted RCU readers blocking the current grace period
* for the specified rcu_node structure. If the caller needs a reliable
* answer, it must hold the rcu_node's ->lock.
*/
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
{
return rnp->gp_tasks != NULL;
}
/*
* Advance a ->blkd_tasks-list pointer to the next entry, instead
* returning NULL if at the end of the list.
*/
static struct list_head *rcu_next_node_entry(struct task_struct *t,
struct rcu_node *rnp)
{
struct list_head *np;
np = t->rcu_node_entry.next;
if (np == &rnp->blkd_tasks)
np = NULL;
return np;
}
/*
* Return true if the specified rcu_node structure has tasks that were
* preempted within an RCU read-side critical section.
*/
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
{
return !list_empty(&rnp->blkd_tasks);
}
/*
* Handle special cases during rcu_read_unlock(), such as needing to
* notify RCU core processing or task having blocked during the RCU
* read-side critical section.
*/
void rcu_read_unlock_special(struct task_struct *t)
{
bool empty_exp;
bool empty_norm;
bool empty_exp_now;
unsigned long flags;
struct list_head *np;
bool drop_boost_mutex = false;
struct rcu_data *rdp;
struct rcu_node *rnp;
union rcu_special special;
/* NMI handlers cannot block and cannot safely manipulate state. */
if (in_nmi())
return;
local_irq_save(flags);
/*
* If RCU core is waiting for this CPU to exit its critical section,
* report the fact that it has exited. Because irqs are disabled,
* t->rcu_read_unlock_special cannot change.
*/
special = t->rcu_read_unlock_special;
if (special.b.need_qs) {
rcu_preempt_qs();
t->rcu_read_unlock_special.b.need_qs = false;
if (!t->rcu_read_unlock_special.s) {
local_irq_restore(flags);
return;
}
}
/*
* Respond to a request for an expedited grace period, but only if
* we were not preempted, meaning that we were running on the same
* CPU throughout. If we were preempted, the exp_need_qs flag
* would have been cleared at the time of the first preemption,
* and the quiescent state would be reported when we were dequeued.
*/
if (special.b.exp_need_qs) {
WARN_ON_ONCE(special.b.blocked);
t->rcu_read_unlock_special.b.exp_need_qs = false;
rdp = this_cpu_ptr(rcu_state_p->rda);
rcu_report_exp_rdp(rcu_state_p, rdp, true);
if (!t->rcu_read_unlock_special.s) {
local_irq_restore(flags);
return;
}
}
/* Hardware IRQ handlers cannot block, complain if they get here. */
if (in_irq() || in_serving_softirq()) {
lockdep_rcu_suspicious(__FILE__, __LINE__,
"rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
t->rcu_read_unlock_special.s,
t->rcu_read_unlock_special.b.blocked,
t->rcu_read_unlock_special.b.exp_need_qs,
t->rcu_read_unlock_special.b.need_qs);
local_irq_restore(flags);
return;
}
/* Clean up if blocked during RCU read-side critical section. */
if (special.b.blocked) {
t->rcu_read_unlock_special.b.blocked = false;
/*
* Remove this task from the list it blocked on. The task
* now remains queued on the rcu_node corresponding to the
* CPU it first blocked on, so there is no longer any need
* to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
*/
rnp = t->rcu_blocked_node;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
WARN_ON_ONCE(rnp != t->rcu_blocked_node);
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
empty_exp = sync_rcu_preempt_exp_done(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
np = rcu_next_node_entry(t, rnp);
list_del_init(&t->rcu_node_entry);
t->rcu_blocked_node = NULL;
trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
rnp->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;
if (IS_ENABLED(CONFIG_RCU_BOOST)) {
if (&t->rcu_node_entry == rnp->boost_tasks)
rnp->boost_tasks = np;
/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
}
/*
* If this was the last task on the current list, and if
* we aren't waiting on any CPUs, report the quiescent state.
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
* so we must take a snapshot of the expedited state.
*/
empty_exp_now = sync_rcu_preempt_exp_done(rnp);
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
rnp->gpnum,
0, rnp->qsmask,
rnp->level,
rnp->grplo,
rnp->grphi,
!!rnp->gp_tasks);
rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);
} else {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
/* Unboost if we were boosted. */
if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
rt_mutex_unlock(&rnp->boost_mtx);
/*
* If this was the last task on the expedited lists,
* then we need to report up the rcu_node hierarchy.
*/
if (!empty_exp && empty_exp_now)
rcu_report_exp_rnp(rcu_state_p, rnp, true);
} else {
local_irq_restore(flags);
}
}
/*
* Dump detailed information for all tasks blocking the current RCU
* grace period on the specified rcu_node structure.
*/
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
unsigned long flags;
struct task_struct *t;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (!rcu_preempt_blocked_readers_cgp(rnp)) {
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
t = list_entry(rnp->gp_tasks->prev,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
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);
}
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
rnp->level, rnp->grplo, rnp->grphi);
}
static void rcu_print_task_stall_end(void)
{
pr_cont("\n");
}
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each.
*/
static int rcu_print_task_stall(struct rcu_node *rnp)
{
struct task_struct *t;
int ndetected = 0;
if (!rcu_preempt_blocked_readers_cgp(rnp))
return 0;
rcu_print_task_stall_begin(rnp);
t = list_entry(rnp->gp_tasks->prev,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
pr_cont(" P%d", t->pid);
ndetected++;
}
rcu_print_task_stall_end();
return ndetected;
}
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each that is blocking the current
* expedited grace period.
*/
static int rcu_print_task_exp_stall(struct rcu_node *rnp)
{
struct task_struct *t;
int ndetected = 0;
if (!rnp->exp_tasks)
return 0;
t = list_entry(rnp->exp_tasks->prev,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
pr_cont(" P%d", t->pid);
ndetected++;
}
return ndetected;
}
/*
* Check that the list of blocked tasks for the newly completed grace
* period is in fact empty. It is a serious bug to complete a grace
* period that still has RCU readers blocked! This function must be
* invoked -before- updating this rnp's ->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 (rcu_preempt_has_tasks(rnp))
rnp->gp_tasks = rnp->blkd_tasks.next;
WARN_ON_ONCE(rnp->qsmask);
}
/*
* Check for a quiescent state from the current CPU. When a task blocks,
* the task is recorded in the corresponding CPU's rcu_node structure,
* which is checked elsewhere.
*
* Caller must disable hard irqs.
*/
static void rcu_preempt_check_callbacks(void)
{
struct task_struct *t = current;
if (t->rcu_read_lock_nesting == 0) {
rcu_preempt_qs();
return;
}
if (t->rcu_read_lock_nesting > 0 &&
__this_cpu_read(rcu_data_p->core_needs_qs) &&
__this_cpu_read(rcu_data_p->cpu_no_qs.b.norm))
t->rcu_read_unlock_special.b.need_qs = true;
}
#ifdef CONFIG_RCU_BOOST
static void rcu_preempt_do_callbacks(void)
{
rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p));
}
#endif /* #ifdef CONFIG_RCU_BOOST */
/*
* Queue a preemptible-RCU callback for invocation after a grace period.
*/
void call_rcu(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, rcu_state_p, -1, 0);
}
EXPORT_SYMBOL_GPL(call_rcu);
/**
* synchronize_rcu - wait until a grace period has elapsed.
*
* Control will return to the caller some time after a full grace
* period has elapsed, in other words after all currently executing RCU
* read-side critical sections have completed. Note, however, that
* upon return from synchronize_rcu(), the caller might well be executing
* concurrently with new RCU read-side critical sections that began while
* synchronize_rcu() was waiting. RCU read-side critical sections are
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
*
* See the description of synchronize_sched() for more detailed information
* on memory ordering guarantees.
*/
void synchronize_rcu(void)
{
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu() in RCU read-side critical section");
if (!rcu_scheduler_active)
return;
if (rcu_gp_is_expedited())
synchronize_rcu_expedited();
else
wait_rcu_gp(call_rcu);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
/*
* Remote handler for smp_call_function_single(). If there is an
* RCU read-side critical section in effect, request that the
* next rcu_read_unlock() record the quiescent state up the
* ->expmask fields in the rcu_node tree. Otherwise, immediately
* report the quiescent state.
*/
static void sync_rcu_exp_handler(void *info)
{
struct rcu_data *rdp;
struct rcu_state *rsp = info;
struct task_struct *t = current;
/*
* Within an RCU read-side critical section, request that the next
* rcu_read_unlock() report. Unless this RCU read-side critical
* section has already blocked, in which case it is already set
* up for the expedited grace period to wait on it.
*/
if (t->rcu_read_lock_nesting > 0 &&
!t->rcu_read_unlock_special.b.blocked) {
t->rcu_read_unlock_special.b.exp_need_qs = true;
return;
}
/*
* We are either exiting an RCU read-side critical section (negative
* values of t->rcu_read_lock_nesting) or are not in one at all
* (zero value of t->rcu_read_lock_nesting). Or we are in an RCU
* read-side critical section that blocked before this expedited
* grace period started. Either way, we can immediately report
* the quiescent state.
*/
rdp = this_cpu_ptr(rsp->rda);
rcu_report_exp_rdp(rsp, rdp, true);
}
/**
* 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.
*/
void synchronize_rcu_expedited(void)
{
struct rcu_node *rnp;
struct rcu_node *rnp_unlock;
struct rcu_state *rsp = rcu_state_p;
unsigned long s;
/* If expedited grace periods are prohibited, fall back to normal. */
if (rcu_gp_is_normal()) {
wait_rcu_gp(call_rcu);
return;
}
s = rcu_exp_gp_seq_snap(rsp);
rnp_unlock = exp_funnel_lock(rsp, s);
if (rnp_unlock == NULL)
return; /* Someone else did our work for us. */
rcu_exp_gp_seq_start(rsp);
/* Initialize the rcu_node tree in preparation for the wait. */
sync_rcu_exp_select_cpus(rsp, sync_rcu_exp_handler);
/* Wait for snapshotted ->blkd_tasks lists to drain. */
rnp = rcu_get_root(rsp);
synchronize_sched_expedited_wait(rsp);
/* Clean up and exit. */
rcu_exp_gp_seq_end(rsp);
mutex_unlock(&rnp_unlock->exp_funnel_mutex);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
/**
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
*
* Note that this primitive does not necessarily wait for an RCU grace period
* to complete. For example, if there are no RCU callbacks queued anywhere
* in the system, then rcu_barrier() is within its rights to return
* immediately, without waiting for anything, much less an RCU grace period.
*/
void rcu_barrier(void)
{
_rcu_barrier(rcu_state_p);
}
EXPORT_SYMBOL_GPL(rcu_barrier);
/*
* Initialize preemptible RCU's state structures.
*/
static void __init __rcu_init_preempt(void)
{
rcu_init_one(rcu_state_p);
}
/*
* Check for a task exiting while in a preemptible-RCU read-side
* critical section, clean up if so. No need to issue warnings,
* as debug_check_no_locks_held() already does this if lockdep
* is enabled.
*/
void exit_rcu(void)
{
struct task_struct *t = current;
if (likely(list_empty(&current->rcu_node_entry)))
return;
t->rcu_read_lock_nesting = 1;
barrier();
t->rcu_read_unlock_special.b.blocked = true;
__rcu_read_unlock();
}
#else /* #ifdef CONFIG_PREEMPT_RCU */
static struct rcu_state *const rcu_state_p = &rcu_sched_state;
static struct rcu_data __percpu *const rcu_data_p = &rcu_sched_data;
/*
* Tell them what RCU they are running.
*/
static void __init rcu_bootup_announce(void)
{
pr_info("Hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
/*
* Because preemptible RCU does not exist, we never have to check for
* CPUs being in quiescent states.
*/
static void rcu_preempt_note_context_switch(void)
{
}
/*
* Because preemptible RCU does not exist, there are never any preempted
* RCU readers.
*/
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
{
return 0;
}
/*
* Because there is no preemptible RCU, there can be no readers blocked.
*/
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
{
return false;
}
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
static int rcu_print_task_stall(struct rcu_node *rnp)
{
return 0;
}
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections that are
* blocking the current expedited grace period.
*/
static int rcu_print_task_exp_stall(struct rcu_node *rnp)
{
return 0;
}
/*
* Because there is no preemptible RCU, there can be no readers blocked,
* so there is no need to check for blocked tasks. So check only for
* bogus qsmask values.
*/
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
WARN_ON_ONCE(rnp->qsmask);
}
/*
* Because preemptible RCU does not exist, it never has any callbacks
* to check.
*/
static void rcu_preempt_check_callbacks(void)
{
}
/*
* 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);
/*
* Because preemptible RCU does not exist, rcu_barrier() is just
* another name for rcu_barrier_sched().
*/
void rcu_barrier(void)
{
rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);
/*
* Because preemptible RCU does not exist, it need not be initialized.
*/
static void __init __rcu_init_preempt(void)
{
}
/*
* Because preemptible RCU does not exist, tasks cannot possibly exit
* while in preemptible RCU read-side critical sections.
*/
void exit_rcu(void)
{
}
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
#ifdef CONFIG_RCU_BOOST
#include "../locking/rtmutex_common.h"
#ifdef CONFIG_RCU_TRACE
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
if (!rcu_preempt_has_tasks(rnp))
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 task_struct *t;
struct list_head *tb;
if (READ_ONCE(rnp->exp_tasks) == NULL &&
READ_ONCE(rnp->boost_tasks) == NULL)
return 0; /* Nothing left to boost. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
/*
* Recheck under the lock: all tasks in need of boosting
* might exit their RCU read-side critical sections on their own.
*/
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
raw_spin_unlock_irqrestore(&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(&rnp->boost_mtx, t);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
/* Lock only for side effect: boosts task t's priority. */
rt_mutex_lock(&rnp->boost_mtx);
rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
return READ_ONCE(rnp->exp_tasks) != NULL ||
READ_ONCE(rnp->boost_tasks) != NULL;
}
/*
* Priority-boosting kthread, one per leaf rcu_node.
*/
static int rcu_boost_kthread(void *arg)
{
struct rcu_node *rnp = (struct rcu_node *)arg;
int spincnt = 0;
int more2boost;
trace_rcu_utilization(TPS("Start boost kthread@init"));
for (;;) {
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
more2boost = rcu_boost(rnp);
if (more2boost)
spincnt++;
else
spincnt = 0;
if (spincnt > 10) {
rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
schedule_timeout_interruptible(2);
trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
spincnt = 0;
}
}
/* NOTREACHED */
trace_rcu_utilization(TPS("End boost kthread@notreached"));
return 0;
}
/*
* Check to see if it is time to start boosting RCU readers that are
* blocking the current grace period, and, if so, tell the per-rcu_node
* kthread to start boosting them. If there is an expedited grace
* period in progress, it is always time to boost.
*
* The caller must hold rnp->lock, which this function releases.
* The ->boost_kthread_task is immortal, so we don't need to worry
* about it going away.
*/
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
__releases(rnp->lock)
{
struct task_struct *t;
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 __this_cpu_read(rcu_cpu_kthread_task) == current;
}
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
/*
* Do priority-boost accounting for the start of a new grace period.
*/
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
}
/*
* Create an RCU-boost kthread for the specified node if one does not
* already exist. We only create this kthread for preemptible RCU.
* Returns zero if all is well, a negated errno otherwise.
*/
static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
struct rcu_node *rnp)
{
int rnp_index = rnp - &rsp->node[0];
unsigned long flags;
struct sched_param sp;
struct task_struct *t;
if (rcu_state_p != rsp)
return 0;
if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
return 0;
rsp->boost = 1;
if (rnp->boost_kthread_task != NULL)
return 0;
t = kthread_create(rcu_boost_kthread, (void *)rnp,
"rcub/%d", rnp_index);
if (IS_ERR(t))
return PTR_ERR(t);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->boost_kthread_task = t;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
return 0;
}
static void rcu_kthread_do_work(void)
{
rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
rcu_preempt_do_callbacks();
}
static void rcu_cpu_kthread_setup(unsigned int cpu)
{
struct sched_param sp;
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
}
static void rcu_cpu_kthread_park(unsigned int cpu)
{
per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
}
static int rcu_cpu_kthread_should_run(unsigned int cpu)
{
return __this_cpu_read(rcu_cpu_has_work);
}
/*
* Per-CPU kernel thread that invokes RCU callbacks. This replaces the
* RCU softirq used in flavors and configurations of RCU that do not
* support RCU priority boosting.
*/
static void rcu_cpu_kthread(unsigned int cpu)
{
unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
int spincnt;
for (spincnt = 0; spincnt < 10; spincnt++) {
trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
local_bh_disable();
*statusp = RCU_KTHREAD_RUNNING;
this_cpu_inc(rcu_cpu_kthread_loops);
local_irq_disable();
work = *workp;
*workp = 0;
local_irq_enable();
if (work)
rcu_kthread_do_work();
local_bh_enable();
if (*workp == 0) {
trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
*statusp = RCU_KTHREAD_WAITING;
return;
}
}
*statusp = RCU_KTHREAD_YIELDING;
trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
schedule_timeout_interruptible(2);
trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
*statusp = RCU_KTHREAD_WAITING;
}
/*
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
* served by the rcu_node in question. The CPU hotplug lock is still
* held, so the value of rnp->qsmaskinit will be stable.
*
* We don't include outgoingcpu in the affinity set, use -1 if there is
* no outgoing CPU. If there are no CPUs left in the affinity set,
* this function allows the kthread to execute on any CPU.
*/
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
struct task_struct *t = rnp->boost_kthread_task;
unsigned long mask = rcu_rnp_online_cpus(rnp);
cpumask_var_t cm;
int cpu;
if (!t)
return;
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
return;
for (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);
set_cpus_allowed_ptr(t, cm);
free_cpumask_var(cm);
}
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
.store = &rcu_cpu_kthread_task,
.thread_should_run = rcu_cpu_kthread_should_run,
.thread_fn = rcu_cpu_kthread,
.thread_comm = "rcuc/%u",
.setup = rcu_cpu_kthread_setup,
.park = rcu_cpu_kthread_park,
};
/*
* Spawn boost kthreads -- called as soon as the scheduler is running.
*/
static void __init rcu_spawn_boost_kthreads(void)
{
struct rcu_node *rnp;
int cpu;
for_each_possible_cpu(cpu)
per_cpu(rcu_cpu_has_work, cpu) = 0;
BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
rcu_for_each_leaf_node(rcu_state_p, rnp)
(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
}
static void rcu_prepare_kthreads(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
struct rcu_node *rnp = rdp->mynode;
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
if (rcu_scheduler_fully_active)
(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
}
#else /* #ifdef CONFIG_RCU_BOOST */
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
__releases(rnp->lock)
{
raw_spin_unlock_irqrestore(&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 void __init rcu_spawn_boost_kthreads(void)
{
}
static void rcu_prepare_kthreads(int cpu)
{
}
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#if !defined(CONFIG_RCU_FAST_NO_HZ)
/*
* Check to see if any future RCU-related work will need to be done
* by the current CPU, even if none need be done immediately, returning
* 1 if so. This function is part of the RCU implementation; it is -not-
* an exported member of the RCU API.
*
* Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
* any flavor of RCU.
*/
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
{
*nextevt = KTIME_MAX;
return IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)
? 0 : rcu_cpu_has_callbacks(NULL);
}
/*
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
* after it.
*/
static void rcu_cleanup_after_idle(void)
{
}
/*
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
* is nothing.
*/
static void rcu_prepare_for_idle(void)
{
}
/*
* Don't bother keeping a running count of the number of RCU callbacks
* posted because CONFIG_RCU_FAST_NO_HZ=n.
*/
static void rcu_idle_count_callbacks_posted(void)
{
}
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
/*
* This code is invoked when a CPU goes idle, at which point we want
* to have the CPU do everything required for RCU so that it can enter
* the energy-efficient dyntick-idle mode. This is handled by a
* state machine implemented by rcu_prepare_for_idle() below.
*
* The following three proprocessor symbols control this state machine:
*
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
* to sleep in dyntick-idle mode with RCU callbacks pending. This
* is sized to be roughly one RCU grace period. Those energy-efficiency
* benchmarkers who might otherwise be tempted to set this to a large
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
* system. And if you are -that- concerned about energy efficiency,
* just power the system down and be done with it!
* RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
* permitted to sleep in dyntick-idle mode with only lazy RCU
* callbacks pending. Setting this too high can OOM your system.
*
* The values below work well in practice. If future workloads require
* adjustment, they can be converted into kernel config parameters, though
* making the state machine smarter might be a better option.
*/
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
module_param(rcu_idle_gp_delay, int, 0644);
static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
module_param(rcu_idle_lazy_gp_delay, int, 0644);
/*
* Try to advance callbacks for all flavors of RCU on the current CPU, but
* only if it has been awhile since the last time we did so. Afterwards,
* if there are any callbacks ready for immediate invocation, return true.
*/
static bool __maybe_unused rcu_try_advance_all_cbs(void)
{
bool cbs_ready = false;
struct rcu_data *rdp;
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
struct rcu_node *rnp;
struct rcu_state *rsp;
/* Exit early if we advanced recently. */
if (jiffies == rdtp->last_advance_all)
return false;
rdtp->last_advance_all = jiffies;
for_each_rcu_flavor(rsp) {
rdp = this_cpu_ptr(rsp->rda);
rnp = rdp->mynode;
/*
* Don't bother checking unless a grace period has
* completed since we last checked and there are
* callbacks not yet ready to invoke.
*/
if ((rdp->completed != rnp->completed ||
unlikely(READ_ONCE(rdp->gpwrap))) &&
rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
note_gp_changes(rsp, rdp);
if (cpu_has_callbacks_ready_to_invoke(rdp))
cbs_ready = true;
}
return cbs_ready;
}
/*
* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
* to invoke. If the CPU has callbacks, try to advance them. Tell the
* caller to set the timeout based on whether or not there are non-lazy
* callbacks.
*
* The caller must have disabled interrupts.
*/
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
unsigned long dj;
if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)) {
*nextevt = KTIME_MAX;
return 0;
}
/* Snapshot to detect later posting of non-lazy callback. */
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
/* If no callbacks, RCU doesn't need the CPU. */
if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
*nextevt = KTIME_MAX;
return 0;
}
/* Attempt to advance callbacks. */
if (rcu_try_advance_all_cbs()) {
/* Some ready to invoke, so initiate later invocation. */
invoke_rcu_core();
return 1;
}
rdtp->last_accelerate = jiffies;
/* Request timer delay depending on laziness, and round. */
if (!rdtp->all_lazy) {
dj = round_up(rcu_idle_gp_delay + jiffies,
rcu_idle_gp_delay) - jiffies;
} else {
dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
}
*nextevt = basemono + dj * TICK_NSEC;
return 0;
}
/*
* Prepare a CPU for idle from an RCU perspective. The first major task
* is to sense whether nohz mode has been enabled or disabled via sysfs.
* The second major task is to check to see if a non-lazy callback has
* arrived at a CPU that previously had only lazy callbacks. The third
* major task is to accelerate (that is, assign grace-period numbers to)
* any recently arrived callbacks.
*
* The caller must have disabled interrupts.
*/
static void rcu_prepare_for_idle(void)
{
bool needwake;
struct rcu_data *rdp;
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
struct rcu_node *rnp;
struct rcu_state *rsp;
int tne;
if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) ||
rcu_is_nocb_cpu(smp_processor_id()))
return;
/* Handle nohz enablement switches conservatively. */
tne = READ_ONCE(tick_nohz_active);
if (tne != rdtp->tick_nohz_enabled_snap) {
if (rcu_cpu_has_callbacks(NULL))
invoke_rcu_core(); /* force nohz to see update. */
rdtp->tick_nohz_enabled_snap = tne;
return;
}
if (!tne)
return;
/*
* If a non-lazy callback arrived at a CPU having only lazy
* callbacks, invoke RCU core for the side-effect of recalculating
* idle duration on re-entry to idle.
*/
if (rdtp->all_lazy &&
rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
rdtp->all_lazy = false;
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
invoke_rcu_core();
return;
}
/*
* If we have not yet accelerated this jiffy, accelerate all
* callbacks on this CPU.
*/
if (rdtp->last_accelerate == jiffies)
return;
rdtp->last_accelerate = jiffies;
for_each_rcu_flavor(rsp) {
rdp = this_cpu_ptr(rsp->rda);
if (!*rdp->nxttail[RCU_DONE_TAIL])
continue;
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
if (needwake)
rcu_gp_kthread_wake(rsp);
}
}
/*
* Clean up for exit from idle. Attempt to advance callbacks based on
* any grace periods that elapsed while the CPU was idle, and if any
* callbacks are now ready to invoke, initiate invocation.
*/
static void rcu_cleanup_after_idle(void)
{
if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) ||
rcu_is_nocb_cpu(smp_processor_id()))
return;
if (rcu_try_advance_all_cbs())
invoke_rcu_core();
}
/*
* Keep a running count of the number of non-lazy callbacks posted
* on this CPU. This running counter (which is never decremented) allows
* rcu_prepare_for_idle() to detect when something out of the idle loop
* posts a callback, even if an equal number of callbacks are invoked.
* Of course, callbacks should only be posted from within a trace event
* designed to be called from idle or from within RCU_NONIDLE().
*/
static void rcu_idle_count_callbacks_posted(void)
{
__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
}
/*
* Data for flushing lazy RCU callbacks at OOM time.
*/
static atomic_t oom_callback_count;
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
/*
* RCU OOM callback -- decrement the outstanding count and deliver the
* wake-up if we are the last one.
*/
static void rcu_oom_callback(struct rcu_head *rhp)
{
if (atomic_dec_and_test(&oom_callback_count))
wake_up(&oom_callback_wq);
}
/*
* Post an rcu_oom_notify callback on the current CPU if it has at
* least one lazy callback. This will unnecessarily post callbacks
* to CPUs that already have a non-lazy callback at the end of their
* callback list, but this is an infrequent operation, so accept some
* extra overhead to keep things simple.
*/
static void rcu_oom_notify_cpu(void *unused)
{
struct rcu_state *rsp;
struct rcu_data *rdp;
for_each_rcu_flavor(rsp) {
rdp = raw_cpu_ptr(rsp->rda);
if (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);
smp_mb(); /* Ensure callback reuse happens after callback invocation. */
/*
* Prevent premature wakeup: ensure that all increments happen
* before there is a chance of the counter reaching zero.
*/
atomic_set(&oom_callback_count, 1);
for_each_online_cpu(cpu) {
smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
cond_resched_rcu_qs();
}
/* Unconditionally decrement: no need to wake ourselves up. */
atomic_dec(&oom_callback_count);
return NOTIFY_OK;
}
static struct notifier_block rcu_oom_nb = {
.notifier_call = rcu_oom_notify
};
static int __init rcu_register_oom_notifier(void)
{
register_oom_notifier(&rcu_oom_nb);
return 0;
}
early_initcall(rcu_register_oom_notifier);
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
#ifdef CONFIG_RCU_FAST_NO_HZ
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
ulong2long(nlpd),
rdtp->all_lazy ? 'L' : '.',
rdtp->tick_nohz_enabled_snap ? '.' : 'D');
}
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
*cp = '\0';
}
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
pr_cont("\n");
}
/*
* Print out diagnostic information for the specified stalled CPU.
*
* If the specified CPU is aware of the current RCU grace period
* (flavor specified by rsp), then print the number of scheduling
* clock interrupts the CPU has taken during the time that it has
* been aware. Otherwise, print the number of RCU grace periods
* that this CPU is ignorant of, for example, "1" if the CPU was
* aware of the previous grace period.
*
* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
*/
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
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);
pr_err("\t%d-%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
cpu,
"O."[!!cpu_online(cpu)],
"o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
"N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
ticks_value, ticks_title,
atomic_read(&rdtp->dynticks) & 0xfff,
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
fast_no_hz);
}
/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
pr_err("\t");
}
/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
rdp->ticks_this_gp = 0;
rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
}
/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
struct rcu_state *rsp;
for_each_rcu_flavor(rsp)
raw_cpu_inc(rsp->rda->ticks_this_gp);
}
#ifdef CONFIG_RCU_NOCB_CPU
/*
* Offload callback processing from the boot-time-specified set of CPUs
* specified by rcu_nocb_mask. For each CPU in the set, there is a
* kthread created that pulls the callbacks from the corresponding CPU,
* waits for a grace period to elapse, and invokes the callbacks.
* The no-CBs CPUs do a wake_up() on their kthread when they insert
* a callback into any empty list, unless the rcu_nocb_poll boot parameter
* has been specified, in which case each kthread actively polls its
* CPU. (Which isn't so great for energy efficiency, but which does
* reduce RCU's overhead on that CPU.)
*
* This is intended to be used in conjunction with Frederic Weisbecker's
* adaptive-idle work, which would seriously reduce OS jitter on CPUs
* running CPU-bound user-mode computations.
*
* Offloading of callback processing could also in theory be used as
* an energy-efficiency measure because CPUs with no RCU callbacks
* queued are more aggressive about entering dyntick-idle mode.
*/
/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
static int __init rcu_nocb_setup(char *str)
{
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
have_rcu_nocb_mask = true;
cpulist_parse(str, rcu_nocb_mask);
return 1;
}
__setup("rcu_nocbs=", rcu_nocb_setup);
static int __init parse_rcu_nocb_poll(char *arg)
{
rcu_nocb_poll = 1;
return 0;
}
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
/*
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
* grace period.
*/
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
}
/*
* Set the root rcu_node structure's ->need_future_gp field
* based on the sum of those of all rcu_node structures. This does
* double-count the root rcu_node structure's requests, but this
* is necessary to handle the possibility of a rcu_nocb_kthread()
* having awakened during the time that the rcu_node structures
* were being updated for the end of the previous grace period.
*/
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
}
static void rcu_init_one_nocb(struct rcu_node *rnp)
{
init_waitqueue_head(&rnp->nocb_gp_wq[0]);
init_waitqueue_head(&rnp->nocb_gp_wq[1]);
}
#ifndef CONFIG_RCU_NOCB_CPU_ALL
/* Is the specified CPU a no-CBs CPU? */
bool rcu_is_nocb_cpu(int cpu)
{
if (have_rcu_nocb_mask)
return cpumask_test_cpu(cpu, rcu_nocb_mask);
return false;
}
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
/*
* Kick the leader kthread for this NOCB group.
*/
static void wake_nocb_leader(struct rcu_data *rdp, bool force)
{
struct rcu_data *rdp_leader = rdp->nocb_leader;
if (!READ_ONCE(rdp_leader->nocb_kthread))
return;
if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) {
/* Prior smp_mb__after_atomic() orders against prior enqueue. */
WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
wake_up(&rdp_leader->nocb_wq);
}
}
/*
* Does the specified CPU need an RCU callback for the specified flavor
* of rcu_barrier()?
*/
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
unsigned long ret;
#ifdef CONFIG_PROVE_RCU
struct rcu_head *rhp;
#endif /* #ifdef CONFIG_PROVE_RCU */
/*
* Check count of all no-CBs callbacks awaiting invocation.
* There needs to be a barrier before this function is called,
* but associated with a prior determination that no more
* callbacks would be posted. In the worst case, the first
* barrier in _rcu_barrier() suffices (but the caller cannot
* necessarily rely on this, not a substitute for the caller
* getting the concurrency design right!). There must also be
* a barrier between the following load an posting of a callback
* (if a callback is in fact needed). This is associated with an
* atomic_inc() in the caller.
*/
ret = atomic_long_read(&rdp->nocb_q_count);
#ifdef CONFIG_PROVE_RCU
rhp = READ_ONCE(rdp->nocb_head);
if (!rhp)
rhp = READ_ONCE(rdp->nocb_gp_head);
if (!rhp)
rhp = READ_ONCE(rdp->nocb_follower_head);
/* Having no rcuo kthread but CBs after scheduler starts is bad! */
if (!READ_ONCE(rdp->nocb_kthread) && rhp &&
rcu_scheduler_fully_active) {
/* RCU callback enqueued before CPU first came online??? */
pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
cpu, rhp->func);
WARN_ON_ONCE(1);
}
#endif /* #ifdef CONFIG_PROVE_RCU */
return !!ret;
}
/*
* Enqueue the specified string of rcu_head structures onto the specified
* CPU's no-CBs lists. The CPU is specified by rdp, the head of the
* string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
* counts are supplied by rhcount and rhcount_lazy.
*
* If warranted, also wake up the kthread servicing this CPUs queues.
*/
static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
struct rcu_head *rhp,
struct rcu_head **rhtp,
int rhcount, int rhcount_lazy,
unsigned long flags)
{
int len;
struct rcu_head **old_rhpp;
struct task_struct *t;
/* Enqueue the callback on the nocb list and update counts. */
atomic_long_add(rhcount, &rdp->nocb_q_count);
/* rcu_barrier() relies on ->nocb_q_count add before xchg. */
old_rhpp = xchg(&rdp->nocb_tail, rhtp);
WRITE_ONCE(*old_rhpp, rhp);
atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
/* If we are not being polled and there is a kthread, awaken it ... */
t = READ_ONCE(rdp->nocb_kthread);
if (rcu_nocb_poll || !t) {
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
TPS("WakeNotPoll"));
return;
}
len = atomic_long_read(&rdp->nocb_q_count);
if (old_rhpp == &rdp->nocb_head) {
if (!irqs_disabled_flags(flags)) {
/* ... if queue was empty ... */
wake_nocb_leader(rdp, false);
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
TPS("WakeEmpty"));
} else {
rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
TPS("WakeEmptyIsDeferred"));
}
rdp->qlen_last_fqs_check = 0;
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
/* ... or if many callbacks queued. */
if (!irqs_disabled_flags(flags)) {
wake_nocb_leader(rdp, true);
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
TPS("WakeOvf"));
} else {
rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE;
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
TPS("WakeOvfIsDeferred"));
}
rdp->qlen_last_fqs_check = LONG_MAX / 2;
} else {
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
}
return;
}
/*
* This is a helper for __call_rcu(), which invokes this when the normal
* callback queue is inoperable. If this is not a no-CBs CPU, this
* function returns failure back to __call_rcu(), which can complain
* appropriately.
*
* Otherwise, this function queues the callback where the corresponding
* "rcuo" kthread can find it.
*/
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
bool lazy, unsigned long flags)
{
if (!rcu_is_nocb_cpu(rdp->cpu))
return false;
__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
if (__is_kfree_rcu_offset((unsigned long)rhp->func))
trace_rcu_kfree_callback(rdp->rsp->name, rhp,
(unsigned long)rhp->func,
-atomic_long_read(&rdp->nocb_q_count_lazy),
-atomic_long_read(&rdp->nocb_q_count));
else
trace_rcu_callback(rdp->rsp->name, rhp,
-atomic_long_read(&rdp->nocb_q_count_lazy),
-atomic_long_read(&rdp->nocb_q_count));
/*
* If called from an extended quiescent state with interrupts
* disabled, invoke the RCU core in order to allow the idle-entry
* deferred-wakeup check to function.
*/
if (irqs_disabled_flags(flags) &&
!rcu_is_watching() &&
cpu_online(smp_processor_id()))
invoke_rcu_core();
return true;
}
/*
* Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
* not a no-CBs CPU.
*/
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
struct rcu_data *rdp,
unsigned long flags)
{
long ql = rsp->qlen;
long qll = rsp->qlen_lazy;
/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
if (!rcu_is_nocb_cpu(smp_processor_id()))
return false;
rsp->qlen = 0;
rsp->qlen_lazy = 0;
/* First, enqueue the donelist, if any. This preserves CB ordering. */
if (rsp->orphan_donelist != NULL) {
__call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
rsp->orphan_donetail, ql, qll, flags);
ql = qll = 0;
rsp->orphan_donelist = NULL;
rsp->orphan_donetail = &rsp->orphan_donelist;
}
if (rsp->orphan_nxtlist != NULL) {
__call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
rsp->orphan_nxttail, ql, qll, flags);
ql = qll = 0;
rsp->orphan_nxtlist = NULL;
rsp->orphan_nxttail = &rsp->orphan_nxtlist;
}
return true;
}
/*
* If necessary, kick off a new grace period, and either way wait
* for a subsequent grace period to complete.
*/
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
{
unsigned long c;
bool d;
unsigned long flags;
bool needwake;
struct rcu_node *rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
needwake = rcu_start_future_gp(rnp, rdp, &c);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (needwake)
rcu_gp_kthread_wake(rdp->rsp);
/*
* Wait for the grace period. Do so interruptibly to avoid messing
* up the load average.
*/
trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
for (;;) {
wait_event_interruptible(
rnp->nocb_gp_wq[c & 0x1],
(d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c)));
if (likely(d))
break;
WARN_ON(signal_pending(current));
trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
}
trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
smp_mb(); /* Ensure that CB invocation happens after GP end. */
}
/*
* Leaders come here to wait for additional callbacks to show up.
* This function does not return until callbacks appear.
*/
static void nocb_leader_wait(struct rcu_data *my_rdp)
{
bool firsttime = true;
bool gotcbs;
struct rcu_data *rdp;
struct rcu_head **tail;
wait_again:
/* Wait for callbacks to appear. */
if (!rcu_nocb_poll) {
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
wait_event_interruptible(my_rdp->nocb_wq,
!READ_ONCE(my_rdp->nocb_leader_sleep));
/* Memory barrier handled by smp_mb() calls below and repoll. */
} else if (firsttime) {
firsttime = false; /* Don't drown trace log with "Poll"! */
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll");
}
/*
* Each pass through the following loop checks a follower for CBs.
* We are our own first follower. Any CBs found are moved to
* nocb_gp_head, where they await a grace period.
*/
gotcbs = false;
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
if (!rdp->nocb_gp_head)
continue; /* No CBs here, try next follower. */
/* Move callbacks to wait-for-GP list, which is empty. */
WRITE_ONCE(rdp->nocb_head, NULL);
rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
gotcbs = true;
}
/*
* If there were no callbacks, sleep a bit, rescan after a
* memory barrier, and go retry.
*/
if (unlikely(!gotcbs)) {
if (!rcu_nocb_poll)
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
"WokeEmpty");
WARN_ON(signal_pending(current));
schedule_timeout_interruptible(1);
/* Rescan in case we were a victim of memory ordering. */
my_rdp->nocb_leader_sleep = true;
smp_mb(); /* Ensure _sleep true before scan. */
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
if (READ_ONCE(rdp->nocb_head)) {
/* Found CB, so short-circuit next wait. */
my_rdp->nocb_leader_sleep = false;
break;
}
goto wait_again;
}
/* Wait for one grace period. */
rcu_nocb_wait_gp(my_rdp);
/*
* We left ->nocb_leader_sleep unset to reduce cache thrashing.
* We set it now, but recheck for new callbacks while
* traversing our follower list.
*/
my_rdp->nocb_leader_sleep = true;
smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
/* Each pass through the following loop wakes a follower, if needed. */
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
if (READ_ONCE(rdp->nocb_head))
my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
if (!rdp->nocb_gp_head)
continue; /* No CBs, so no need to wake follower. */
/* Append callbacks to follower's "done" list. */
tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
*tail = rdp->nocb_gp_head;
smp_mb__after_atomic(); /* Store *tail before wakeup. */
if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
/*
* List was empty, wake up the follower.
* Memory barriers supplied by atomic_long_add().
*/
wake_up(&rdp->nocb_wq);
}
}
/* If we (the leader) don't have CBs, go wait some more. */
if (!my_rdp->nocb_follower_head)
goto wait_again;
}
/*
* Followers come here to wait for additional callbacks to show up.
* This function does not return until callbacks appear.
*/
static void nocb_follower_wait(struct rcu_data *rdp)
{
bool firsttime = true;
for (;;) {
if (!rcu_nocb_poll) {
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
"FollowerSleep");
wait_event_interruptible(rdp->nocb_wq,
READ_ONCE(rdp->nocb_follower_head));
} else if (firsttime) {
/* Don't drown trace log with "Poll"! */
firsttime = false;
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll");
}
if (smp_load_acquire(&rdp->nocb_follower_head)) {
/* ^^^ Ensure CB invocation follows _head test. */
return;
}
if (!rcu_nocb_poll)
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
"WokeEmpty");
WARN_ON(signal_pending(current));
schedule_timeout_interruptible(1);
}
}
/*
* Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
* callbacks queued by the corresponding no-CBs CPU, however, there is
* an optional leader-follower relationship so that the grace-period
* kthreads don't have to do quite so many wakeups.
*/
static int rcu_nocb_kthread(void *arg)
{
int c, cl;
struct rcu_head *list;
struct rcu_head *next;
struct rcu_head **tail;
struct rcu_data *rdp = arg;
/* Each pass through this loop invokes one batch of callbacks */
for (;;) {
/* Wait for callbacks. */
if (rdp->nocb_leader == rdp)
nocb_leader_wait(rdp);
else
nocb_follower_wait(rdp);
/* Pull the ready-to-invoke callbacks onto local list. */
list = READ_ONCE(rdp->nocb_follower_head);
BUG_ON(!list);
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
WRITE_ONCE(rdp->nocb_follower_head, NULL);
tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
/* Each pass through the following loop invokes a callback. */
trace_rcu_batch_start(rdp->rsp->name,
atomic_long_read(&rdp->nocb_q_count_lazy),
atomic_long_read(&rdp->nocb_q_count), -1);
c = cl = 0;
while (list) {
next = list->next;
/* Wait for enqueuing to complete, if needed. */
while (next == NULL && &list->next != tail) {
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
TPS("WaitQueue"));
schedule_timeout_interruptible(1);
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
TPS("WokeQueue"));
next = list->next;
}
debug_rcu_head_unqueue(list);
local_bh_disable();
if (__rcu_reclaim(rdp->rsp->name, list))
cl++;
c++;
local_bh_enable();
list = next;
}
trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
smp_mb__before_atomic(); /* _add after CB invocation. */
atomic_long_add(-c, &rdp->nocb_q_count);
atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
rdp->n_nocbs_invoked += c;
}
return 0;
}
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
{
return READ_ONCE(rdp->nocb_defer_wakeup);
}
/* Do a deferred wakeup of rcu_nocb_kthread(). */
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
int ndw;
if (!rcu_nocb_need_deferred_wakeup(rdp))
return;
ndw = READ_ONCE(rdp->nocb_defer_wakeup);
WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_NOT);
wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE);
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
}
void __init rcu_init_nohz(void)
{
int cpu;
bool need_rcu_nocb_mask = true;
struct rcu_state *rsp;
#ifdef CONFIG_RCU_NOCB_CPU_NONE
need_rcu_nocb_mask = false;
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
need_rcu_nocb_mask = true;
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
if (!have_rcu_nocb_mask && need_rcu_nocb_mask) {
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
return;
}
have_rcu_nocb_mask = true;
}
if (!have_rcu_nocb_mask)
return;
#ifdef CONFIG_RCU_NOCB_CPU_ZERO
pr_info("\tOffload RCU callbacks from CPU 0\n");
cpumask_set_cpu(0, rcu_nocb_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
#ifdef CONFIG_RCU_NOCB_CPU_ALL
pr_info("\tOffload RCU callbacks from all CPUs\n");
cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running)
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
cpumask_and(rcu_nocb_mask, cpu_possible_mask,
rcu_nocb_mask);
}
pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
cpumask_pr_args(rcu_nocb_mask));
if (rcu_nocb_poll)
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
for_each_rcu_flavor(rsp) {
for_each_cpu(cpu, rcu_nocb_mask)
init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
rcu_organize_nocb_kthreads(rsp);
}
}
/* Initialize per-rcu_data variables for no-CBs CPUs. */
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
rdp->nocb_tail = &rdp->nocb_head;
init_waitqueue_head(&rdp->nocb_wq);
rdp->nocb_follower_tail = &rdp->nocb_follower_head;
}
/*
* If the specified CPU is a no-CBs CPU that does not already have its
* rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
* brought online out of order, this can require re-organizing the
* leader-follower relationships.
*/
static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
{
struct rcu_data *rdp;
struct rcu_data *rdp_last;
struct rcu_data *rdp_old_leader;
struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
struct task_struct *t;
/*
* If this isn't a no-CBs CPU or if it already has an rcuo kthread,
* then nothing to do.
*/
if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
return;
/* If we didn't spawn the leader first, reorganize! */
rdp_old_leader = rdp_spawn->nocb_leader;
if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
rdp_last = NULL;
rdp = rdp_old_leader;
do {
rdp->nocb_leader = rdp_spawn;
if (rdp_last && rdp != rdp_spawn)
rdp_last->nocb_next_follower = rdp;
if (rdp == rdp_spawn) {
rdp = rdp->nocb_next_follower;
} else {
rdp_last = rdp;
rdp = rdp->nocb_next_follower;
rdp_last->nocb_next_follower = NULL;
}
} while (rdp);
rdp_spawn->nocb_next_follower = rdp_old_leader;
}
/* Spawn the kthread for this CPU and RCU flavor. */
t = kthread_run(rcu_nocb_kthread, rdp_spawn,
"rcuo%c/%d", rsp->abbr, cpu);
BUG_ON(IS_ERR(t));
WRITE_ONCE(rdp_spawn->nocb_kthread, t);
}
/*
* If the specified CPU is a no-CBs CPU that does not already have its
* rcuo kthreads, spawn them.
*/
static void rcu_spawn_all_nocb_kthreads(int cpu)
{
struct rcu_state *rsp;
if (rcu_scheduler_fully_active)
for_each_rcu_flavor(rsp)
rcu_spawn_one_nocb_kthread(rsp, cpu);
}
/*
* Once the scheduler is running, spawn rcuo kthreads for all online
* no-CBs CPUs. This assumes that the early_initcall()s happen before
* non-boot CPUs come online -- if this changes, we will need to add
* some mutual exclusion.
*/
static void __init rcu_spawn_nocb_kthreads(void)
{
int cpu;
for_each_online_cpu(cpu)
rcu_spawn_all_nocb_kthreads(cpu);
}
/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
static int rcu_nocb_leader_stride = -1;
module_param(rcu_nocb_leader_stride, int, 0444);
/*
* Initialize leader-follower relationships for all no-CBs CPU.
*/
static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
{
int cpu;
int ls = rcu_nocb_leader_stride;
int nl = 0; /* Next leader. */
struct rcu_data *rdp;
struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
struct rcu_data *rdp_prev = NULL;
if (!have_rcu_nocb_mask)
return;
if (ls == -1) {
ls = int_sqrt(nr_cpu_ids);
rcu_nocb_leader_stride = ls;
}
/*
* Each pass through this loop sets up one rcu_data structure and
* spawns one rcu_nocb_kthread().
*/
for_each_cpu(cpu, rcu_nocb_mask) {
rdp = per_cpu_ptr(rsp->rda, cpu);
if (rdp->cpu >= nl) {
/* New leader, set up for followers & next leader. */
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
rdp->nocb_leader = rdp;
rdp_leader = rdp;
} else {
/* Another follower, link to previous leader. */
rdp->nocb_leader = rdp_leader;
rdp_prev->nocb_next_follower = rdp;
}
rdp_prev = rdp;
}
}
/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
static bool init_nocb_callback_list(struct rcu_data *rdp)
{
if (!rcu_is_nocb_cpu(rdp->cpu))
return false;
/* If there are early-boot callbacks, move them to nocb lists. */
if (rdp->nxtlist) {
rdp->nocb_head = rdp->nxtlist;
rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL];
atomic_long_set(&rdp->nocb_q_count, rdp->qlen);
atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy);
rdp->nxtlist = NULL;
rdp->qlen = 0;
rdp->qlen_lazy = 0;
}
rdp->nxttail[RCU_NEXT_TAIL] = NULL;
return true;
}
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
{
WARN_ON_ONCE(1); /* Should be dead code. */
return false;
}
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
}
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
}
static void rcu_init_one_nocb(struct rcu_node *rnp)
{
}
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
bool lazy, unsigned long flags)
{
return false;
}
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
struct rcu_data *rdp,
unsigned long flags)
{
return false;
}
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
}
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
{
return false;
}
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
}
static void rcu_spawn_all_nocb_kthreads(int cpu)
{
}
static void __init rcu_spawn_nocb_kthreads(void)
{
}
static bool init_nocb_callback_list(struct rcu_data *rdp)
{
return false;
}
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
/*
* An adaptive-ticks CPU can potentially execute in kernel mode for an
* arbitrarily long period of time with the scheduling-clock tick turned
* off. RCU will be paying attention to this CPU because it is in the
* kernel, but the CPU cannot be guaranteed to be executing the RCU state
* machine because the scheduling-clock tick has been disabled. Therefore,
* if an adaptive-ticks CPU is failing to respond to the current grace
* period and has not be idle from an RCU perspective, kick it.
*/
static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
{
#ifdef CONFIG_NO_HZ_FULL
if (tick_nohz_full_cpu(cpu))
smp_send_reschedule(cpu);
#endif /* #ifdef CONFIG_NO_HZ_FULL */
}
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
static int full_sysidle_state; /* Current system-idle state. */
#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
/*
* Invoked to note exit from irq or task transition to idle. Note that
* usermode execution does -not- count as idle here! After all, we want
* to detect full-system idle states, not RCU quiescent states and grace
* periods. The caller must have disabled interrupts.
*/
static void rcu_sysidle_enter(int irq)
{
unsigned long j;
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
/* If there are no nohz_full= CPUs, no need to track this. */
if (!tick_nohz_full_enabled())
return;
/* Adjust nesting, check for fully idle. */
if (irq) {
rdtp->dynticks_idle_nesting--;
WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
if (rdtp->dynticks_idle_nesting != 0)
return; /* Still not fully idle. */
} else {
if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
DYNTICK_TASK_NEST_VALUE) {
rdtp->dynticks_idle_nesting = 0;
} else {
rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
return; /* Still not fully idle. */
}
}
/* Record start of fully idle period. */
j = jiffies;
WRITE_ONCE(rdtp->dynticks_idle_jiffies, j);
smp_mb__before_atomic();
atomic_inc(&rdtp->dynticks_idle);
smp_mb__after_atomic();
WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
}
/*
* Unconditionally force exit from full system-idle state. This is
* invoked when a normal CPU exits idle, but must be called separately
* for the timekeeping CPU (tick_do_timer_cpu). The reason for this
* is that the timekeeping CPU is permitted to take scheduling-clock
* interrupts while the system is in system-idle state, and of course
* rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
* interrupt from any other type of interrupt.
*/
void rcu_sysidle_force_exit(void)
{
int oldstate = READ_ONCE(full_sysidle_state);
int newoldstate;
/*
* Each pass through the following loop attempts to exit full
* system-idle state. If contention proves to be a problem,
* a trylock-based contention tree could be used here.
*/
while (oldstate > RCU_SYSIDLE_SHORT) {
newoldstate = cmpxchg(&full_sysidle_state,
oldstate, RCU_SYSIDLE_NOT);
if (oldstate == newoldstate &&
oldstate == RCU_SYSIDLE_FULL_NOTED) {
rcu_kick_nohz_cpu(tick_do_timer_cpu);
return; /* We cleared it, done! */
}
oldstate = newoldstate;
}
smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
}
/*
* Invoked to note entry to irq or task transition from idle. Note that
* usermode execution does -not- count as idle here! The caller must
* have disabled interrupts.
*/
static void rcu_sysidle_exit(int irq)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
/* If there are no nohz_full= CPUs, no need to track this. */
if (!tick_nohz_full_enabled())
return;
/* Adjust nesting, check for already non-idle. */
if (irq) {
rdtp->dynticks_idle_nesting++;
WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
if (rdtp->dynticks_idle_nesting != 1)
return; /* Already non-idle. */
} else {
/*
* Allow for irq misnesting. Yes, it really is possible
* to enter an irq handler then never leave it, and maybe
* also vice versa. Handle both possibilities.
*/
if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
return; /* Already non-idle. */
} else {
rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
}
}
/* Record end of idle period. */
smp_mb__before_atomic();
atomic_inc(&rdtp->dynticks_idle);
smp_mb__after_atomic();
WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
/*
* If we are the timekeeping CPU, we are permitted to be non-idle
* during a system-idle state. This must be the case, because
* the timekeeping CPU has to take scheduling-clock interrupts
* during the time that the system is transitioning to full
* system-idle state. This means that the timekeeping CPU must
* invoke rcu_sysidle_force_exit() directly if it does anything
* more than take a scheduling-clock interrupt.
*/
if (smp_processor_id() == tick_do_timer_cpu)
return;
/* Update system-idle state: We are clearly no longer fully idle! */
rcu_sysidle_force_exit();
}
/*
* Check to see if the current CPU is idle. Note that usermode execution
* does not count as idle. The caller must have disabled interrupts,
* and must be running on tick_do_timer_cpu.
*/
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
unsigned long *maxj)
{
int cur;
unsigned long j;
struct rcu_dynticks *rdtp = rdp->dynticks;
/* If there are no nohz_full= CPUs, don't check system-wide idleness. */
if (!tick_nohz_full_enabled())
return;
/*
* If some other CPU has already reported non-idle, if this is
* not the flavor of RCU that tracks sysidle state, or if this
* is an offline or the timekeeping CPU, nothing to do.
*/
if (!*isidle || rdp->rsp != rcu_state_p ||
cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
return;
/* Verify affinity of current kthread. */
WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
/* Pick up current idle and NMI-nesting counter and check. */
cur = atomic_read(&rdtp->dynticks_idle);
if (cur & 0x1) {
*isidle = false; /* We are not idle! */
return;
}
smp_mb(); /* Read counters before timestamps. */
/* Pick up timestamps. */
j = READ_ONCE(rdtp->dynticks_idle_jiffies);
/* If this CPU entered idle more recently, update maxj timestamp. */
if (ULONG_CMP_LT(*maxj, j))
*maxj = j;
}
/*
* Is this the flavor of RCU that is handling full-system idle?
*/
static bool is_sysidle_rcu_state(struct rcu_state *rsp)
{
return rsp == rcu_state_p;
}
/*
* Return a delay in jiffies based on the number of CPUs, rcu_node
* leaf fanout, and jiffies tick rate. The idea is to allow larger
* systems more time to transition to full-idle state in order to
* avoid the cache thrashing that otherwise occur on the state variable.
* Really small systems (less than a couple of tens of CPUs) should
* instead use a single global atomically incremented counter, and later
* versions of this will automatically reconfigure themselves accordingly.
*/
static unsigned long rcu_sysidle_delay(void)
{
if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
return 0;
return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
}
/*
* Advance the full-system-idle state. This is invoked when all of
* the non-timekeeping CPUs are idle.
*/
static void rcu_sysidle(unsigned long j)
{
/* Check the current state. */
switch (READ_ONCE(full_sysidle_state)) {
case RCU_SYSIDLE_NOT:
/* First time all are idle, so note a short idle period. */
WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_SHORT);
break;
case RCU_SYSIDLE_SHORT:
/*
* Idle for a bit, time to advance to next state?
* cmpxchg failure means race with non-idle, let them win.
*/
if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
(void)cmpxchg(&full_sysidle_state,
RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
break;
case RCU_SYSIDLE_LONG:
/*
* Do an additional check pass before advancing to full.
* cmpxchg failure means race with non-idle, let them win.
*/
if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
(void)cmpxchg(&full_sysidle_state,
RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
break;
default:
break;
}
}
/*
* Found a non-idle non-timekeeping CPU, so kick the system-idle state
* back to the beginning.
*/
static void rcu_sysidle_cancel(void)
{
smp_mb();
if (full_sysidle_state > RCU_SYSIDLE_SHORT)
WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_NOT);
}
/*
* Update the sysidle state based on the results of a force-quiescent-state
* scan of the CPUs' dyntick-idle state.
*/
static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
unsigned long maxj, bool gpkt)
{
if (rsp != rcu_state_p)
return; /* Wrong flavor, ignore. */
if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
return; /* Running state machine from timekeeping CPU. */
if (isidle)
rcu_sysidle(maxj); /* More idle! */
else
rcu_sysidle_cancel(); /* Idle is over. */
}
/*
* Wrapper for rcu_sysidle_report() when called from the grace-period
* kthread's context.
*/
static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
unsigned long maxj)
{
/* If there are no nohz_full= CPUs, no need to track this. */
if (!tick_nohz_full_enabled())
return;
rcu_sysidle_report(rsp, isidle, maxj, true);
}
/* Callback and function for forcing an RCU grace period. */
struct rcu_sysidle_head {
struct rcu_head rh;
int inuse;
};
static void rcu_sysidle_cb(struct rcu_head *rhp)
{
struct rcu_sysidle_head *rshp;
/*
* The following memory barrier is needed to replace the
* memory barriers that would normally be in the memory
* allocator.
*/
smp_mb(); /* grace period precedes setting inuse. */
rshp = container_of(rhp, struct rcu_sysidle_head, rh);
WRITE_ONCE(rshp->inuse, 0);
}
/*
* Check to see if the system is fully idle, other than the timekeeping CPU.
* The caller must have disabled interrupts. This is not intended to be
* called unless tick_nohz_full_enabled().
*/
bool rcu_sys_is_idle(void)
{
static struct rcu_sysidle_head rsh;
int rss = READ_ONCE(full_sysidle_state);
if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
return false;
/* Handle small-system case by doing a full scan of CPUs. */
if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
int oldrss = rss - 1;
/*
* One pass to advance to each state up to _FULL.
* Give up if any pass fails to advance the state.
*/
while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
int cpu;
bool isidle = true;
unsigned long maxj = jiffies - ULONG_MAX / 4;
struct rcu_data *rdp;
/* Scan all the CPUs looking for nonidle CPUs. */
for_each_possible_cpu(cpu) {
rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
if (!isidle)
break;
}
rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
oldrss = rss;
rss = READ_ONCE(full_sysidle_state);
}
}
/* If this is the first observation of an idle period, record it. */
if (rss == RCU_SYSIDLE_FULL) {
rss = cmpxchg(&full_sysidle_state,
RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
return rss == RCU_SYSIDLE_FULL;
}
smp_mb(); /* ensure rss load happens before later caller actions. */
/* If already fully idle, tell the caller (in case of races). */
if (rss == RCU_SYSIDLE_FULL_NOTED)
return true;
/*
* If we aren't there yet, and a grace period is not in flight,
* initiate a grace period. Either way, tell the caller that
* we are not there yet. We use an xchg() rather than an assignment
* to make up for the memory barriers that would otherwise be
* provided by the memory allocator.
*/
if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
!rcu_gp_in_progress(rcu_state_p) &&
!rsh.inuse && xchg(&rsh.inuse, 1) == 0)
call_rcu(&rsh.rh, rcu_sysidle_cb);
return false;
}
/*
* Initialize dynticks sysidle state for CPUs coming online.
*/
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
{
rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
}
#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
static void rcu_sysidle_enter(int irq)
{
}
static void rcu_sysidle_exit(int irq)
{
}<