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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-14 22:36:40 +07:00
sched: Replace rq::wake_list
The recent commit: 90b5363acd
("sched: Clean up scheduler_ipi()")
got smp_call_function_single_async() subtly wrong. Even though it will
return -EBUSY when trying to re-use a csd, that condition is not
atomic and still requires external serialization.
The change in ttwu_queue_remote() got this wrong.
While on first reading ttwu_queue_remote() has an atomic test-and-set
that appears to serialize the use, the matching 'release' is not in
the right place to actually guarantee this serialization.
The actual race is vs the sched_ttwu_pending() call in the idle loop;
that can run the wakeup-list without consuming the CSD.
Instead of trying to chain the lists, merge them.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200526161908.129371594@infradead.org
This commit is contained in:
parent
126c2092e5
commit
a148866489
@ -654,6 +654,7 @@ struct task_struct {
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#ifdef CONFIG_SMP
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struct llist_node wake_entry;
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unsigned int wake_entry_type;
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int on_cpu;
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#ifdef CONFIG_THREAD_INFO_IN_TASK
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/* Current CPU: */
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@ -25,6 +25,7 @@ enum {
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CSD_TYPE_ASYNC = 0x00,
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CSD_TYPE_SYNC = 0x10,
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CSD_TYPE_IRQ_WORK = 0x20,
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CSD_TYPE_TTWU = 0x30,
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CSD_FLAG_TYPE_MASK = 0xF0,
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};
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@ -1538,7 +1538,7 @@ static int migration_cpu_stop(void *data)
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* __migrate_task() such that we will not miss enforcing cpus_ptr
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* during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test.
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*/
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sched_ttwu_pending();
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flush_smp_call_function_from_idle();
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raw_spin_lock(&p->pi_lock);
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rq_lock(rq, &rf);
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@ -2272,14 +2272,13 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
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}
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#ifdef CONFIG_SMP
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void sched_ttwu_pending(void)
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void sched_ttwu_pending(void *arg)
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{
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struct llist_node *llist = arg;
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struct rq *rq = this_rq();
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struct llist_node *llist;
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struct task_struct *p, *t;
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struct rq_flags rf;
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llist = llist_del_all(&rq->wake_list);
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if (!llist)
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return;
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@ -2299,11 +2298,6 @@ void sched_ttwu_pending(void)
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rq_unlock_irqrestore(rq, &rf);
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}
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static void wake_csd_func(void *info)
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{
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sched_ttwu_pending();
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}
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void send_call_function_single_ipi(int cpu)
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{
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struct rq *rq = cpu_rq(cpu);
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@ -2327,12 +2321,7 @@ static void __ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags
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p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
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WRITE_ONCE(rq->ttwu_pending, 1);
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if (llist_add(&p->wake_entry, &rq->wake_list)) {
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if (!set_nr_if_polling(rq->idle))
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smp_call_function_single_async(cpu, &rq->wake_csd);
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else
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trace_sched_wake_idle_without_ipi(cpu);
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}
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__smp_call_single_queue(cpu, &p->wake_entry);
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}
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void wake_up_if_idle(int cpu)
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@ -2772,6 +2761,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
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p->capture_control = NULL;
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#endif
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init_numa_balancing(clone_flags, p);
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#ifdef CONFIG_SMP
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p->wake_entry_type = CSD_TYPE_TTWU;
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#endif
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}
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DEFINE_STATIC_KEY_FALSE(sched_numa_balancing);
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@ -6564,7 +6556,6 @@ int sched_cpu_dying(unsigned int cpu)
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struct rq_flags rf;
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/* Handle pending wakeups and then migrate everything off */
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sched_ttwu_pending();
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sched_tick_stop(cpu);
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rq_lock_irqsave(rq, &rf);
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@ -6763,8 +6754,6 @@ void __init sched_init(void)
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rq->avg_idle = 2*sysctl_sched_migration_cost;
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rq->max_idle_balance_cost = sysctl_sched_migration_cost;
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rq_csd_init(rq, &rq->wake_csd, wake_csd_func);
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INIT_LIST_HEAD(&rq->cfs_tasks);
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rq_attach_root(rq, &def_root_domain);
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@ -294,7 +294,6 @@ static void do_idle(void)
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* critical section.
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*/
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flush_smp_call_function_from_idle();
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sched_ttwu_pending();
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schedule_idle();
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if (unlikely(klp_patch_pending(current)))
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@ -1023,11 +1023,6 @@ struct rq {
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unsigned int ttwu_local;
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#endif
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#ifdef CONFIG_SMP
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call_single_data_t wake_csd;
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struct llist_head wake_list;
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#endif
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#ifdef CONFIG_CPU_IDLE
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/* Must be inspected within a rcu lock section */
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struct cpuidle_state *idle_state;
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@ -1371,8 +1366,6 @@ queue_balance_callback(struct rq *rq,
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rq->balance_callback = head;
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}
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extern void sched_ttwu_pending(void);
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#define rcu_dereference_check_sched_domain(p) \
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rcu_dereference_check((p), \
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lockdep_is_held(&sched_domains_mutex))
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@ -1512,7 +1505,6 @@ extern void flush_smp_call_function_from_idle(void);
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#else /* !CONFIG_SMP: */
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static inline void flush_smp_call_function_from_idle(void) { }
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static inline void sched_ttwu_pending(void) { }
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#endif
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#include "stats.h"
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47
kernel/smp.c
47
kernel/smp.c
@ -196,6 +196,7 @@ void generic_smp_call_function_single_interrupt(void)
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flush_smp_call_function_queue(true);
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}
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extern void sched_ttwu_pending(void *);
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extern void irq_work_single(void *);
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/**
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@ -244,6 +245,10 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
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csd->func);
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break;
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case CSD_TYPE_TTWU:
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pr_warn("IPI task-wakeup sent to offline CPU\n");
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break;
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default:
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pr_warn("IPI callback, unknown type %d, sent to offline CPU\n",
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CSD_TYPE(csd));
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@ -275,22 +280,43 @@ static void flush_smp_call_function_queue(bool warn_cpu_offline)
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}
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}
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if (!entry)
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return;
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/*
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* Second; run all !SYNC callbacks.
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*/
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prev = NULL;
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llist_for_each_entry_safe(csd, csd_next, entry, llist) {
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int type = CSD_TYPE(csd);
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if (type == CSD_TYPE_ASYNC) {
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smp_call_func_t func = csd->func;
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void *info = csd->info;
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if (type != CSD_TYPE_TTWU) {
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if (prev) {
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prev->next = &csd_next->llist;
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} else {
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entry = &csd_next->llist;
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}
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csd_unlock(csd);
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func(info);
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} else if (type == CSD_TYPE_IRQ_WORK) {
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irq_work_single(csd);
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if (type == CSD_TYPE_ASYNC) {
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smp_call_func_t func = csd->func;
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void *info = csd->info;
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csd_unlock(csd);
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func(info);
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} else if (type == CSD_TYPE_IRQ_WORK) {
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irq_work_single(csd);
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}
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} else {
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prev = &csd->llist;
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}
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}
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/*
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* Third; only CSD_TYPE_TTWU is left, issue those.
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*/
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if (entry)
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sched_ttwu_pending(entry);
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}
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void flush_smp_call_function_from_idle(void)
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@ -659,6 +685,13 @@ void __init smp_init(void)
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BUILD_BUG_ON(offsetof(struct irq_work, flags) !=
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offsetof(struct __call_single_data, flags));
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/*
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* Assert the CSD_TYPE_TTWU layout is similar enough
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* for task_struct to be on the @call_single_queue.
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*/
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BUILD_BUG_ON(offsetof(struct task_struct, wake_entry_type) - offsetof(struct task_struct, wake_entry) !=
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offsetof(struct __call_single_data, flags) - offsetof(struct __call_single_data, llist));
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idle_threads_init();
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cpuhp_threads_init();
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