linux/kernel/rcu/tree_plugin.h
Peter Zijlstra 7663ad9a5d rcu: Always inline rcu_dynticks_task*_{enter,exit}()
RCU managed to grow a few noinstr violations:

  vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x0: call to rcu_dynticks_task_trace_enter() leaves .noinstr.text section
  vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0xe: call to rcu_dynticks_task_trace_exit() leaves .noinstr.text section

Fix them by adding __always_inline to the relevant trivial functions.

Also replace the noinstr with __always_inline for the existing
rcu_dynticks_task_*() functions since noinstr would force noinline
them, even when empty, which seems silly.

Fixes: 7d0c9c50c5 ("rcu-tasks: Avoid IPIing userspace/idle tasks if kernel is so built")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-10-07 09:59:41 -07:00

1514 lines
48 KiB
C

/* SPDX-License-Identifier: GPL-2.0+ */
/*
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
* Internal non-public definitions that provide either classic
* or preemptible semantics.
*
* Copyright Red Hat, 2009
* Copyright IBM Corporation, 2009
*
* Author: Ingo Molnar <mingo@elte.hu>
* Paul E. McKenney <paulmck@linux.ibm.com>
*/
#include "../locking/rtmutex_common.h"
static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
{
/*
* In order to read the offloaded state of an rdp is a safe
* and stable way and prevent from its value to be changed
* under us, we must either hold the barrier mutex, the cpu
* hotplug lock (read or write) or the nocb lock. Local
* non-preemptible reads are also safe. NOCB kthreads and
* timers have their own means of synchronization against the
* offloaded state updaters.
*/
RCU_LOCKDEP_WARN(
!(lockdep_is_held(&rcu_state.barrier_mutex) ||
(IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
rcu_lockdep_is_held_nocb(rdp) ||
(rdp == this_cpu_ptr(&rcu_data) &&
!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) ||
rcu_current_is_nocb_kthread(rdp)),
"Unsafe read of RCU_NOCB offloaded state"
);
return rcu_segcblist_is_offloaded(&rdp->cblist);
}
/*
* 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 event 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_STRICT_GRACE_PERIOD))
pr_info("\tRCU strict (and thus non-scalable) grace periods enabled.\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=%u.\n", NR_CPUS, nr_cpu_ids);
#ifdef CONFIG_RCU_BOOST
pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
kthread_prio, CONFIG_RCU_BOOST_DELAY);
#endif
if (blimit != DEFAULT_RCU_BLIMIT)
pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
if (qhimark != DEFAULT_RCU_QHIMARK)
pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
if (qlowmark != DEFAULT_RCU_QLOMARK)
pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
if (qovld != DEFAULT_RCU_QOVLD)
pr_info("\tBoot-time adjustment of callback overload level to %ld.\n", qovld);
if (jiffies_till_first_fqs != ULONG_MAX)
pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
if (jiffies_till_next_fqs != ULONG_MAX)
pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
if (jiffies_till_sched_qs != ULONG_MAX)
pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);
if (rcu_kick_kthreads)
pr_info("\tKick kthreads if too-long grace period.\n");
if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
if (gp_preinit_delay)
pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
if (gp_init_delay)
pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
if (gp_cleanup_delay)
pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
if (!use_softirq)
pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
pr_info("\tRCU debug extended QS entry/exit.\n");
rcupdate_announce_bootup_oddness();
}
#ifdef CONFIG_PREEMPT_RCU
static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
static void rcu_read_unlock_special(struct task_struct *t);
/*
* 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;
raw_lockdep_assert_held_rcu_node(rnp);
WARN_ON_ONCE(rdp->mynode != rnp);
WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
/* RCU better not be waiting on newly onlined CPUs! */
WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
rdp->grpmask);
/*
* 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)) {
WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry);
WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
}
if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
WRITE_ONCE(rnp->exp_tasks, &t->rcu_node_entry);
WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
!(rnp->qsmask & rdp->grpmask));
WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
!(rnp->expmask & rdp->grpmask));
raw_spin_unlock_rcu_node(rnp); /* interrupts 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 && rdp->exp_deferred_qs)
rcu_report_exp_rdp(rdp);
else
WARN_ON_ONCE(rdp->exp_deferred_qs);
}
/*
* Record a preemptible-RCU quiescent state for the specified CPU.
* Note that this does not necessarily mean that the task currently running
* on the CPU is in a quiescent state: Instead, it means that the current
* grace period need not wait on any RCU read-side critical section that
* starts later on this CPU. It also means that if the current task is
* in an RCU read-side critical section, it has already added itself to
* some leaf rcu_node structure's ->blkd_tasks list. In addition to the
* current task, there might be any number of other tasks blocked while
* in an RCU read-side critical section.
*
* Callers to this function must disable preemption.
*/
static void rcu_qs(void)
{
RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {
trace_rcu_grace_period(TPS("rcu_preempt"),
__this_cpu_read(rcu_data.gp_seq),
TPS("cpuqs"));
__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
WRITE_ONCE(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.
*/
void rcu_note_context_switch(bool preempt)
{
struct task_struct *t = current;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp;
trace_rcu_utilization(TPS("Start context switch"));
lockdep_assert_irqs_disabled();
WARN_ONCE(!preempt && rcu_preempt_depth() > 0, "Voluntary context switch within RCU read-side critical section!");
if (rcu_preempt_depth() > 0 &&
!t->rcu_read_unlock_special.b.blocked) {
/* Possibly blocking in an RCU read-side critical section. */
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(rcu_state.name,
t->pid,
(rnp->qsmask & rdp->grpmask)
? rnp->gp_seq
: rcu_seq_snap(&rnp->gp_seq));
rcu_preempt_ctxt_queue(rnp, rdp);
} else {
rcu_preempt_deferred_qs(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_qs();
if (rdp->exp_deferred_qs)
rcu_report_exp_rdp(rdp);
rcu_tasks_qs(current, preempt);
trace_rcu_utilization(TPS("End context switch"));
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
/*
* 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 READ_ONCE(rnp->gp_tasks) != NULL;
}
/* limit value for ->rcu_read_lock_nesting. */
#define RCU_NEST_PMAX (INT_MAX / 2)
static void rcu_preempt_read_enter(void)
{
WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1);
}
static int rcu_preempt_read_exit(void)
{
int ret = READ_ONCE(current->rcu_read_lock_nesting) - 1;
WRITE_ONCE(current->rcu_read_lock_nesting, ret);
return ret;
}
static void rcu_preempt_depth_set(int val)
{
WRITE_ONCE(current->rcu_read_lock_nesting, val);
}
/*
* Preemptible RCU implementation for rcu_read_lock().
* Just increment ->rcu_read_lock_nesting, shared state will be updated
* if we block.
*/
void __rcu_read_lock(void)
{
rcu_preempt_read_enter();
if (IS_ENABLED(CONFIG_PROVE_LOCKING))
WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && rcu_state.gp_kthread)
WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true);
barrier(); /* critical section after entry code. */
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);
/*
* Preemptible RCU implementation for rcu_read_unlock().
* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
* invoke rcu_read_unlock_special() to clean up after a context switch
* in an RCU read-side critical section and other special cases.
*/
void __rcu_read_unlock(void)
{
struct task_struct *t = current;
barrier(); // critical section before exit code.
if (rcu_preempt_read_exit() == 0) {
barrier(); // critical-section exit before .s check.
if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
rcu_read_unlock_special(t);
}
if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
int rrln = rcu_preempt_depth();
WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX);
}
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
/*
* 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);
}
/*
* Report deferred quiescent states. The deferral time can
* be quite short, for example, in the case of the call from
* rcu_read_unlock_special().
*/
static void
rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
{
bool empty_exp;
bool empty_norm;
bool empty_exp_now;
struct list_head *np;
bool drop_boost_mutex = false;
struct rcu_data *rdp;
struct rcu_node *rnp;
union rcu_special special;
/*
* 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;
rdp = this_cpu_ptr(&rcu_data);
if (!special.s && !rdp->exp_deferred_qs) {
local_irq_restore(flags);
return;
}
t->rcu_read_unlock_special.s = 0;
if (special.b.need_qs) {
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
rcu_report_qs_rdp(rdp);
udelay(rcu_unlock_delay);
} else {
rcu_qs();
}
}
/*
* Respond to a request by an expedited grace period for a
* quiescent state from this CPU. Note that requests from
* tasks are handled when removing the task from the
* blocked-tasks list below.
*/
if (rdp->exp_deferred_qs)
rcu_report_exp_rdp(rdp);
/* Clean up if blocked during RCU read-side critical section. */
if (special.b.blocked) {
/*
* 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);
WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
(!empty_norm || rnp->qsmask));
empty_exp = sync_rcu_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->gp_seq, t->pid);
if (&t->rcu_node_entry == rnp->gp_tasks)
WRITE_ONCE(rnp->gp_tasks, np);
if (&t->rcu_node_entry == rnp->exp_tasks)
WRITE_ONCE(rnp->exp_tasks, np);
if (IS_ENABLED(CONFIG_RCU_BOOST)) {
/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t;
if (&t->rcu_node_entry == rnp->boost_tasks)
WRITE_ONCE(rnp->boost_tasks, np);
}
/*
* 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_exp_done(rnp);
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
rnp->gp_seq,
0, rnp->qsmask,
rnp->level,
rnp->grplo,
rnp->grphi,
!!rnp->gp_tasks);
rcu_report_unblock_qs_rnp(rnp, flags);
} else {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
/* Unboost if we were boosted. */
if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
rt_mutex_futex_unlock(&rnp->boost_mtx.rtmutex);
/*
* 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(rnp, true);
} else {
local_irq_restore(flags);
}
}
/*
* Is a deferred quiescent-state pending, and are we also not in
* an RCU read-side critical section? It is the caller's responsibility
* to ensure it is otherwise safe to report any deferred quiescent
* states. The reason for this is that it is safe to report a
* quiescent state during context switch even though preemption
* is disabled. This function cannot be expected to understand these
* nuances, so the caller must handle them.
*/
static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
{
return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
READ_ONCE(t->rcu_read_unlock_special.s)) &&
rcu_preempt_depth() == 0;
}
/*
* Report a deferred quiescent state if needed and safe to do so.
* As with rcu_preempt_need_deferred_qs(), "safe" involves only
* not being in an RCU read-side critical section. The caller must
* evaluate safety in terms of interrupt, softirq, and preemption
* disabling.
*/
static void rcu_preempt_deferred_qs(struct task_struct *t)
{
unsigned long flags;
if (!rcu_preempt_need_deferred_qs(t))
return;
local_irq_save(flags);
rcu_preempt_deferred_qs_irqrestore(t, flags);
}
/*
* Minimal handler to give the scheduler a chance to re-evaluate.
*/
static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
{
struct rcu_data *rdp;
rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
rdp->defer_qs_iw_pending = false;
}
/*
* Handle special cases during rcu_read_unlock(), such as needing to
* notify RCU core processing or task having blocked during the RCU
* read-side critical section.
*/
static void rcu_read_unlock_special(struct task_struct *t)
{
unsigned long flags;
bool irqs_were_disabled;
bool preempt_bh_were_disabled =
!!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
/* NMI handlers cannot block and cannot safely manipulate state. */
if (in_nmi())
return;
local_irq_save(flags);
irqs_were_disabled = irqs_disabled_flags(flags);
if (preempt_bh_were_disabled || irqs_were_disabled) {
bool expboost; // Expedited GP in flight or possible boosting.
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
expboost = (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) ||
(rdp->grpmask & READ_ONCE(rnp->expmask)) ||
IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ||
(IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled &&
t->rcu_blocked_node);
// Need to defer quiescent state until everything is enabled.
if (use_softirq && (in_irq() || (expboost && !irqs_were_disabled))) {
// Using softirq, safe to awaken, and either the
// wakeup is free or there is either an expedited
// GP in flight or a potential need to deboost.
raise_softirq_irqoff(RCU_SOFTIRQ);
} else {
// Enabling BH or preempt does reschedule, so...
// Also if no expediting and no possible deboosting,
// slow is OK. Plus nohz_full CPUs eventually get
// tick enabled.
set_tsk_need_resched(current);
set_preempt_need_resched();
if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
// Get scheduler to re-evaluate and call hooks.
// If !IRQ_WORK, FQS scan will eventually IPI.
init_irq_work(&rdp->defer_qs_iw, rcu_preempt_deferred_qs_handler);
rdp->defer_qs_iw_pending = true;
irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
}
}
local_irq_restore(flags);
return;
}
rcu_preempt_deferred_qs_irqrestore(t, flags);
}
/*
* 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 ->gp_seq.
*
* 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)
{
struct task_struct *t;
RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
raw_lockdep_assert_held_rcu_node(rnp);
if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
dump_blkd_tasks(rnp, 10);
if (rcu_preempt_has_tasks(rnp) &&
(rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
t = container_of(rnp->gp_tasks, struct task_struct,
rcu_node_entry);
trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
rnp->gp_seq, t->pid);
}
WARN_ON_ONCE(rnp->qsmask);
}
/*
* Check for a quiescent state from the current CPU, including voluntary
* context switches for Tasks RCU. When a task blocks, the task is
* recorded in the corresponding CPU's rcu_node structure, which is checked
* elsewhere, hence this function need only check for quiescent states
* related to the current CPU, not to those related to tasks.
*/
static void rcu_flavor_sched_clock_irq(int user)
{
struct task_struct *t = current;
lockdep_assert_irqs_disabled();
if (user || rcu_is_cpu_rrupt_from_idle()) {
rcu_note_voluntary_context_switch(current);
}
if (rcu_preempt_depth() > 0 ||
(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
/* No QS, force context switch if deferred. */
if (rcu_preempt_need_deferred_qs(t)) {
set_tsk_need_resched(t);
set_preempt_need_resched();
}
} else if (rcu_preempt_need_deferred_qs(t)) {
rcu_preempt_deferred_qs(t); /* Report deferred QS. */
return;
} else if (!WARN_ON_ONCE(rcu_preempt_depth())) {
rcu_qs(); /* Report immediate QS. */
return;
}
/* If GP is oldish, ask for help from rcu_read_unlock_special(). */
if (rcu_preempt_depth() > 0 &&
__this_cpu_read(rcu_data.core_needs_qs) &&
__this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
!t->rcu_read_unlock_special.b.need_qs &&
time_after(jiffies, rcu_state.gp_start + HZ))
t->rcu_read_unlock_special.b.need_qs = true;
}
/*
* 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.
* Besides, if this function does anything other than just immediately
* return, there was a bug of some sort. Spewing warnings from this
* function is like as not to simply obscure important prior warnings.
*/
void exit_rcu(void)
{
struct task_struct *t = current;
if (unlikely(!list_empty(&current->rcu_node_entry))) {
rcu_preempt_depth_set(1);
barrier();
WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
} else if (unlikely(rcu_preempt_depth())) {
rcu_preempt_depth_set(1);
} else {
return;
}
__rcu_read_unlock();
rcu_preempt_deferred_qs(current);
}
/*
* Dump the blocked-tasks state, but limit the list dump to the
* specified number of elements.
*/
static void
dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
{
int cpu;
int i;
struct list_head *lhp;
bool onl;
struct rcu_data *rdp;
struct rcu_node *rnp1;
raw_lockdep_assert_held_rcu_node(rnp);
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
__func__, rnp->grplo, rnp->grphi, rnp->level,
(long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs);
for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
__func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks),
READ_ONCE(rnp->exp_tasks));
pr_info("%s: ->blkd_tasks", __func__);
i = 0;
list_for_each(lhp, &rnp->blkd_tasks) {
pr_cont(" %p", lhp);
if (++i >= ncheck)
break;
}
pr_cont("\n");
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
rdp = per_cpu_ptr(&rcu_data, cpu);
onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
cpu, ".o"[onl],
(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
}
}
#else /* #ifdef CONFIG_PREEMPT_RCU */
/*
* If strict grace periods are enabled, and if the calling
* __rcu_read_unlock() marks the beginning of a quiescent state, immediately
* report that quiescent state and, if requested, spin for a bit.
*/
void rcu_read_unlock_strict(void)
{
struct rcu_data *rdp;
if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
return;
rdp = this_cpu_ptr(&rcu_data);
rcu_report_qs_rdp(rdp);
udelay(rcu_unlock_delay);
}
EXPORT_SYMBOL_GPL(rcu_read_unlock_strict);
/*
* Tell them what RCU they are running.
*/
static void __init rcu_bootup_announce(void)
{
pr_info("Hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
/*
* Note a quiescent state for PREEMPTION=n. Because we do not need to know
* how many quiescent states passed, just if there was at least one since
* the start of the grace period, this just sets a flag. The caller must
* have disabled preemption.
*/
static void rcu_qs(void)
{
RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
return;
trace_rcu_grace_period(TPS("rcu_sched"),
__this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
return;
__this_cpu_write(rcu_data.cpu_no_qs.b.exp, false);
rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
}
/*
* Register an urgently needed quiescent state. If there is an
* emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
* dyntick-idle quiescent state visible to other CPUs, which will in
* some cases serve for expedited as well as normal grace periods.
* Either way, register a lightweight quiescent state.
*/
void rcu_all_qs(void)
{
unsigned long flags;
if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
return;
preempt_disable();
/* Load rcu_urgent_qs before other flags. */
if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
preempt_enable();
return;
}
this_cpu_write(rcu_data.rcu_urgent_qs, false);
if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
local_irq_save(flags);
rcu_momentary_dyntick_idle();
local_irq_restore(flags);
}
rcu_qs();
preempt_enable();
}
EXPORT_SYMBOL_GPL(rcu_all_qs);
/*
* Note a PREEMPTION=n context switch. The caller must have disabled interrupts.
*/
void rcu_note_context_switch(bool preempt)
{
trace_rcu_utilization(TPS("Start context switch"));
rcu_qs();
/* Load rcu_urgent_qs before other flags. */
if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
goto out;
this_cpu_write(rcu_data.rcu_urgent_qs, false);
if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
rcu_momentary_dyntick_idle();
rcu_tasks_qs(current, preempt);
out:
trace_rcu_utilization(TPS("End context switch"));
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
/*
* 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 there is no preemptible RCU, there can be no deferred quiescent
* states.
*/
static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
{
return false;
}
static void rcu_preempt_deferred_qs(struct task_struct *t) { }
/*
* 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);
}
/*
* Check to see if this CPU is in a non-context-switch quiescent state,
* namely user mode and idle loop.
*/
static void rcu_flavor_sched_clock_irq(int user)
{
if (user || rcu_is_cpu_rrupt_from_idle()) {
/*
* Get here if this CPU took its interrupt from user
* mode or from the idle loop, and if this is not a
* nested interrupt. In this case, the CPU is in
* a quiescent state, so note it.
*
* No memory barrier is required here because rcu_qs()
* references only CPU-local variables that other CPUs
* neither access nor modify, at least not while the
* corresponding CPU is online.
*/
rcu_qs();
}
}
/*
* Because preemptible RCU does not exist, tasks cannot possibly exit
* while in preemptible RCU read-side critical sections.
*/
void exit_rcu(void)
{
}
/*
* Dump the guaranteed-empty blocked-tasks state. Trust but verify.
*/
static void
dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
{
WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
}
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
/*
* If boosting, set rcuc kthreads to realtime priority.
*/
static void rcu_cpu_kthread_setup(unsigned int cpu)
{
#ifdef CONFIG_RCU_BOOST
struct sched_param sp;
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
#endif /* #ifdef CONFIG_RCU_BOOST */
}
#ifdef CONFIG_RCU_BOOST
/*
* 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_rcu_node(rnp, 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;
else
tb = rnp->boost_tasks;
/*
* 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.rtmutex, t);
raw_spin_unlock_irqrestore_rcu_node(rnp, 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. */
rnp->n_boosts++;
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 (;;) {
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
rcu_wait(READ_ONCE(rnp->boost_tasks) ||
READ_ONCE(rnp->exp_tasks));
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
more2boost = rcu_boost(rnp);
if (more2boost)
spincnt++;
else
spincnt = 0;
if (spincnt > 10) {
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING);
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
schedule_timeout_idle(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)
{
raw_lockdep_assert_held_rcu_node(rnp);
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
if (rnp->exp_tasks != NULL ||
(rnp->gp_tasks != NULL &&
rnp->boost_tasks == NULL &&
rnp->qsmask == 0 &&
(!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld))) {
if (rnp->exp_tasks == NULL)
WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rcu_wake_cond(rnp->boost_kthread_task,
READ_ONCE(rnp->boost_kthread_status));
} else {
raw_spin_unlock_irqrestore_rcu_node(rnp, 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_data.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 void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
{
unsigned long flags;
int rnp_index = rnp - rcu_get_root();
struct sched_param sp;
struct task_struct *t;
if (rnp->boost_kthread_task || !rcu_scheduler_fully_active)
return;
rcu_state.boost = 1;
t = kthread_create(rcu_boost_kthread, (void *)rnp,
"rcub/%d", rnp_index);
if (WARN_ON_ONCE(IS_ERR(t)))
return;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->boost_kthread_task = t;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
}
/*
* 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_each_leaf_node_possible_cpu(rnp, cpu)
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
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);
}
/*
* Spawn boost kthreads -- called as soon as the scheduler is running.
*/
static void __init rcu_spawn_boost_kthreads(void)
{
struct rcu_node *rnp;
rcu_for_each_leaf_node(rnp)
if (rcu_rnp_online_cpus(rnp))
rcu_spawn_one_boost_kthread(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_rcu_node(rnp, flags);
}
static bool rcu_is_callbacks_kthread(void)
{
return false;
}
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}
static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
{
}
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
}
static void __init rcu_spawn_boost_kthreads(void)
{
}
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#if !defined(CONFIG_RCU_FAST_NO_HZ)
/*
* Check to see if any future non-offloaded 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 or not this
* CPU has RCU callbacks queued.
*/
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
{
*nextevt = KTIME_MAX;
return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
!rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));
}
/*
* 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)
{
}
#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.
*
* The following preprocessor symbol controls this:
*
* 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!
*
* The value below works 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. */
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
module_param(rcu_idle_gp_delay, int, 0644);
/*
* Try to advance callbacks 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 = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp;
/* Exit early if we advanced recently. */
if (jiffies == rdp->last_advance_all)
return false;
rdp->last_advance_all = jiffies;
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 ((rcu_seq_completed_gp(rdp->gp_seq,
rcu_seq_current(&rnp->gp_seq)) ||
unlikely(READ_ONCE(rdp->gpwrap))) &&
rcu_segcblist_pend_cbs(&rdp->cblist))
note_gp_changes(rdp);
if (rcu_segcblist_ready_cbs(&rdp->cblist))
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 about what to set the timeout.
*
* The caller must have disabled interrupts.
*/
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
unsigned long dj;
lockdep_assert_irqs_disabled();
/* If no non-offloaded callbacks, RCU doesn't need the CPU. */
if (rcu_segcblist_empty(&rdp->cblist) ||
rcu_rdp_is_offloaded(rdp)) {
*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;
}
rdp->last_accelerate = jiffies;
/* Request timer and round. */
dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - 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 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 = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp;
int tne;
lockdep_assert_irqs_disabled();
if (rcu_rdp_is_offloaded(rdp))
return;
/* Handle nohz enablement switches conservatively. */
tne = READ_ONCE(tick_nohz_active);
if (tne != rdp->tick_nohz_enabled_snap) {
if (!rcu_segcblist_empty(&rdp->cblist))
invoke_rcu_core(); /* force nohz to see update. */
rdp->tick_nohz_enabled_snap = tne;
return;
}
if (!tne)
return;
/*
* If we have not yet accelerated this jiffy, accelerate all
* callbacks on this CPU.
*/
if (rdp->last_accelerate == jiffies)
return;
rdp->last_accelerate = jiffies;
if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
needwake = rcu_accelerate_cbs(rnp, rdp);
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
if (needwake)
rcu_gp_kthread_wake();
}
}
/*
* 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)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
lockdep_assert_irqs_disabled();
if (rcu_rdp_is_offloaded(rdp))
return;
if (rcu_try_advance_all_cbs())
invoke_rcu_core();
}
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
/*
* Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
* grace-period kthread will do force_quiescent_state() processing?
* The idea is to avoid waking up RCU core processing on such a
* CPU unless the grace period has extended for too long.
*
* This code relies on the fact that all NO_HZ_FULL CPUs are also
* CONFIG_RCU_NOCB_CPU CPUs.
*/
static bool rcu_nohz_full_cpu(void)
{
#ifdef CONFIG_NO_HZ_FULL
if (tick_nohz_full_cpu(smp_processor_id()) &&
(!rcu_gp_in_progress() ||
time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
return true;
#endif /* #ifdef CONFIG_NO_HZ_FULL */
return false;
}
/*
* Bind the RCU grace-period kthreads to the housekeeping CPU.
*/
static void rcu_bind_gp_kthread(void)
{
if (!tick_nohz_full_enabled())
return;
housekeeping_affine(current, HK_FLAG_RCU);
}
/* Record the current task on dyntick-idle entry. */
static __always_inline void rcu_dynticks_task_enter(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}
/* Record no current task on dyntick-idle exit. */
static __always_inline void rcu_dynticks_task_exit(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}
/* Turn on heavyweight RCU tasks trace readers on idle/user entry. */
static __always_inline void rcu_dynticks_task_trace_enter(void)
{
#ifdef CONFIG_TASKS_TRACE_RCU
if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
current->trc_reader_special.b.need_mb = true;
#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
}
/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
static __always_inline void rcu_dynticks_task_trace_exit(void)
{
#ifdef CONFIG_TASKS_TRACE_RCU
if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
current->trc_reader_special.b.need_mb = false;
#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
}