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![Thomas Gleixner](/assets/img/avatar_default.png)
The smpboot threads rely on the park/unpark mechanism which binds per cpu threads on a particular core. Though the functionality is racy: CPU0 CPU1 CPU2 unpark(T) wake_up_process(T) clear(SHOULD_PARK) T runs leave parkme() due to !SHOULD_PARK bind_to(CPU2) BUG_ON(wrong CPU) We cannot let the tasks move themself to the target CPU as one of those tasks is actually the migration thread itself, which requires that it starts running on the target cpu right away. The solution to this problem is to prevent wakeups in park mode which are not from unpark(). That way we can guarantee that the association of the task to the target cpu is working correctly. Add a new task state (TASK_PARKED) which prevents other wakeups and use this state explicitly for the unpark wakeup. Peter noticed: Also, since the task state is visible to userspace and all the parked tasks are still in the PID space, its a good hint in ps and friends that these tasks aren't really there for the moment. The migration thread has another related issue. CPU0 CPU1 Bring up CPU2 create_thread(T) park(T) wait_for_completion() parkme() complete() sched_set_stop_task() schedule(TASK_PARKED) The sched_set_stop_task() call is issued while the task is on the runqueue of CPU1 and that confuses the hell out of the stop_task class on that cpu. So we need the same synchronizaion before sched_set_stop_task(). Reported-by: Dave Jones <davej@redhat.com> Reported-and-tested-by: Dave Hansen <dave@sr71.net> Reported-and-tested-by: Borislav Petkov <bp@alien8.de> Acked-by: Peter Ziljstra <peterz@infradead.org> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Cc: dhillf@gmail.com Cc: Ingo Molnar <mingo@kernel.org> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1304091635430.21884@ionos Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
313 lines
6.9 KiB
C
313 lines
6.9 KiB
C
/*
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* Common SMP CPU bringup/teardown functions
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*/
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#include <linux/cpu.h>
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#include <linux/err.h>
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#include <linux/smp.h>
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#include <linux/init.h>
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#include <linux/list.h>
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#include <linux/slab.h>
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#include <linux/sched.h>
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#include <linux/export.h>
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#include <linux/percpu.h>
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#include <linux/kthread.h>
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#include <linux/smpboot.h>
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#include "smpboot.h"
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#ifdef CONFIG_SMP
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#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
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/*
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* For the hotplug case we keep the task structs around and reuse
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* them.
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*/
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static DEFINE_PER_CPU(struct task_struct *, idle_threads);
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struct task_struct * __cpuinit idle_thread_get(unsigned int cpu)
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{
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struct task_struct *tsk = per_cpu(idle_threads, cpu);
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if (!tsk)
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return ERR_PTR(-ENOMEM);
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init_idle(tsk, cpu);
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return tsk;
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}
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void __init idle_thread_set_boot_cpu(void)
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{
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per_cpu(idle_threads, smp_processor_id()) = current;
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}
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/**
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* idle_init - Initialize the idle thread for a cpu
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* @cpu: The cpu for which the idle thread should be initialized
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*
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* Creates the thread if it does not exist.
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*/
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static inline void idle_init(unsigned int cpu)
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{
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struct task_struct *tsk = per_cpu(idle_threads, cpu);
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if (!tsk) {
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tsk = fork_idle(cpu);
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if (IS_ERR(tsk))
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pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
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else
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per_cpu(idle_threads, cpu) = tsk;
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}
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}
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/**
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* idle_threads_init - Initialize idle threads for all cpus
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*/
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void __init idle_threads_init(void)
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{
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unsigned int cpu, boot_cpu;
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boot_cpu = smp_processor_id();
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for_each_possible_cpu(cpu) {
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if (cpu != boot_cpu)
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idle_init(cpu);
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}
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}
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#endif
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#endif /* #ifdef CONFIG_SMP */
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static LIST_HEAD(hotplug_threads);
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static DEFINE_MUTEX(smpboot_threads_lock);
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struct smpboot_thread_data {
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unsigned int cpu;
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unsigned int status;
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struct smp_hotplug_thread *ht;
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};
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enum {
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HP_THREAD_NONE = 0,
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HP_THREAD_ACTIVE,
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HP_THREAD_PARKED,
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};
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/**
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* smpboot_thread_fn - percpu hotplug thread loop function
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* @data: thread data pointer
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*
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* Checks for thread stop and park conditions. Calls the necessary
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* setup, cleanup, park and unpark functions for the registered
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* thread.
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*
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* Returns 1 when the thread should exit, 0 otherwise.
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*/
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static int smpboot_thread_fn(void *data)
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{
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struct smpboot_thread_data *td = data;
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struct smp_hotplug_thread *ht = td->ht;
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while (1) {
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set_current_state(TASK_INTERRUPTIBLE);
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preempt_disable();
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if (kthread_should_stop()) {
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set_current_state(TASK_RUNNING);
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preempt_enable();
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if (ht->cleanup)
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ht->cleanup(td->cpu, cpu_online(td->cpu));
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kfree(td);
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return 0;
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}
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if (kthread_should_park()) {
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__set_current_state(TASK_RUNNING);
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preempt_enable();
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if (ht->park && td->status == HP_THREAD_ACTIVE) {
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BUG_ON(td->cpu != smp_processor_id());
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ht->park(td->cpu);
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td->status = HP_THREAD_PARKED;
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}
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kthread_parkme();
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/* We might have been woken for stop */
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continue;
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}
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BUG_ON(td->cpu != smp_processor_id());
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/* Check for state change setup */
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switch (td->status) {
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case HP_THREAD_NONE:
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preempt_enable();
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if (ht->setup)
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ht->setup(td->cpu);
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td->status = HP_THREAD_ACTIVE;
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preempt_disable();
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break;
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case HP_THREAD_PARKED:
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preempt_enable();
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if (ht->unpark)
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ht->unpark(td->cpu);
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td->status = HP_THREAD_ACTIVE;
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preempt_disable();
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break;
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}
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if (!ht->thread_should_run(td->cpu)) {
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preempt_enable();
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schedule();
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} else {
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set_current_state(TASK_RUNNING);
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preempt_enable();
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ht->thread_fn(td->cpu);
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}
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}
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}
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static int
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__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
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{
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struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
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struct smpboot_thread_data *td;
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if (tsk)
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return 0;
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td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
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if (!td)
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return -ENOMEM;
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td->cpu = cpu;
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td->ht = ht;
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tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
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ht->thread_comm);
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if (IS_ERR(tsk)) {
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kfree(td);
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return PTR_ERR(tsk);
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}
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get_task_struct(tsk);
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*per_cpu_ptr(ht->store, cpu) = tsk;
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if (ht->create) {
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/*
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* Make sure that the task has actually scheduled out
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* into park position, before calling the create
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* callback. At least the migration thread callback
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* requires that the task is off the runqueue.
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*/
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if (!wait_task_inactive(tsk, TASK_PARKED))
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WARN_ON(1);
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else
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ht->create(cpu);
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}
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return 0;
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}
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int smpboot_create_threads(unsigned int cpu)
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{
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struct smp_hotplug_thread *cur;
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int ret = 0;
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mutex_lock(&smpboot_threads_lock);
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list_for_each_entry(cur, &hotplug_threads, list) {
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ret = __smpboot_create_thread(cur, cpu);
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if (ret)
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break;
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}
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mutex_unlock(&smpboot_threads_lock);
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return ret;
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}
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static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
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{
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struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
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if (ht->pre_unpark)
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ht->pre_unpark(cpu);
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kthread_unpark(tsk);
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}
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void smpboot_unpark_threads(unsigned int cpu)
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{
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struct smp_hotplug_thread *cur;
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mutex_lock(&smpboot_threads_lock);
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list_for_each_entry(cur, &hotplug_threads, list)
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smpboot_unpark_thread(cur, cpu);
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mutex_unlock(&smpboot_threads_lock);
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}
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static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
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{
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struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
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if (tsk && !ht->selfparking)
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kthread_park(tsk);
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}
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void smpboot_park_threads(unsigned int cpu)
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{
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struct smp_hotplug_thread *cur;
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mutex_lock(&smpboot_threads_lock);
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list_for_each_entry_reverse(cur, &hotplug_threads, list)
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smpboot_park_thread(cur, cpu);
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mutex_unlock(&smpboot_threads_lock);
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}
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static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
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{
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unsigned int cpu;
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/* We need to destroy also the parked threads of offline cpus */
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for_each_possible_cpu(cpu) {
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struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
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if (tsk) {
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kthread_stop(tsk);
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put_task_struct(tsk);
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*per_cpu_ptr(ht->store, cpu) = NULL;
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}
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}
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}
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/**
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* smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
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* @plug_thread: Hotplug thread descriptor
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*
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* Creates and starts the threads on all online cpus.
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*/
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int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
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{
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unsigned int cpu;
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int ret = 0;
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mutex_lock(&smpboot_threads_lock);
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for_each_online_cpu(cpu) {
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ret = __smpboot_create_thread(plug_thread, cpu);
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if (ret) {
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smpboot_destroy_threads(plug_thread);
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goto out;
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}
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smpboot_unpark_thread(plug_thread, cpu);
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}
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list_add(&plug_thread->list, &hotplug_threads);
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out:
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mutex_unlock(&smpboot_threads_lock);
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return ret;
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}
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EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
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/**
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* smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
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* @plug_thread: Hotplug thread descriptor
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*
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* Stops all threads on all possible cpus.
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*/
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void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
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{
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get_online_cpus();
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mutex_lock(&smpboot_threads_lock);
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list_del(&plug_thread->list);
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smpboot_destroy_threads(plug_thread);
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mutex_unlock(&smpboot_threads_lock);
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put_online_cpus();
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}
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EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
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