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Commit 5be9361c authored by Gautham R Shenoy's avatar Gautham R Shenoy Committed by Linus Torvalds
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Eliminate lock_cpu_hotplug in kernel/schedc 



Eliminate lock_cpu_hotplug from kernel/sched.c and use sched_hotcpu_mutex
instead to postpone a hotplug event.

In the migration_call hotcpu callback function, take sched_hotcpu_mutex
while handling the event CPU_LOCK_ACQUIRE and release it while handling
CPU_LOCK_RELEASE event.

[akpm@linux-foundation.org: fix deadlock]
Signed-off-by: default avatarGautham R Shenoy <ego@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent baaca49f

kernel/sched.c

+18 −10
Original line number Diff line number Diff line
@@ -305,6 +305,7 @@ struct rq { 
};



static DEFINE_PER_CPU(struct rq, runqueues) ____cacheline_aligned_in_smp;

static DEFINE_MUTEX(sched_hotcpu_mutex);



static inline int cpu_of(struct rq *rq)

{
@@ -4520,13 +4521,13 @@ long sched_setaffinity(pid_t pid, cpumask_t new_mask) 
	struct task_struct *p;

	int retval;



	lock_cpu_hotplug();

	mutex_lock(&sched_hotcpu_mutex);

	read_lock(&tasklist_lock);



	p = find_process_by_pid(pid);

	if (!p) {

		read_unlock(&tasklist_lock);

		unlock_cpu_hotplug();

		mutex_unlock(&sched_hotcpu_mutex);

		return -ESRCH;

	}
@@ -4553,7 +4554,7 @@ long sched_setaffinity(pid_t pid, cpumask_t new_mask) 


out_unlock:

	put_task_struct(p);

	unlock_cpu_hotplug();

	mutex_unlock(&sched_hotcpu_mutex);

	return retval;

}
@@ -4610,7 +4611,7 @@ long sched_getaffinity(pid_t pid, cpumask_t *mask) 
	struct task_struct *p;

	int retval;



	lock_cpu_hotplug();

	mutex_lock(&sched_hotcpu_mutex);

	read_lock(&tasklist_lock);



	retval = -ESRCH;
@@ -4626,7 +4627,7 @@ long sched_getaffinity(pid_t pid, cpumask_t *mask) 


out_unlock:

	read_unlock(&tasklist_lock);

	unlock_cpu_hotplug();

	mutex_unlock(&sched_hotcpu_mutex);

	if (retval)

		return retval;
@@ -5388,6 +5389,10 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) 
	struct rq *rq;



	switch (action) {

	case CPU_LOCK_ACQUIRE:

		mutex_lock(&sched_hotcpu_mutex);

		break;



	case CPU_UP_PREPARE:

		p = kthread_create(migration_thread, hcpu, "migration/%d",cpu);

		if (IS_ERR(p))
@@ -5433,7 +5438,7 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) 
		BUG_ON(rq->nr_running != 0);



		/* No need to migrate the tasks: it was best-effort if

		 * they didn't do lock_cpu_hotplug().  Just wake up

		 * they didn't take sched_hotcpu_mutex.  Just wake up

		 * the requestors. */

		spin_lock_irq(&rq->lock);

		while (!list_empty(&rq->migration_queue)) {
@@ -5447,6 +5452,9 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) 
		spin_unlock_irq(&rq->lock);

		break;

#endif

	case CPU_LOCK_RELEASE:

		mutex_unlock(&sched_hotcpu_mutex);

		break;

	}

	return NOTIFY_OK;

}
@@ -6822,10 +6830,10 @@ int arch_reinit_sched_domains(void) 
{

	int err;



	lock_cpu_hotplug();

	mutex_lock(&sched_hotcpu_mutex);

	detach_destroy_domains(&cpu_online_map);

	err = arch_init_sched_domains(&cpu_online_map);

	unlock_cpu_hotplug();

	mutex_unlock(&sched_hotcpu_mutex);



	return err;

}
@@ -6930,12 +6938,12 @@ void __init sched_init_smp(void) 
{

	cpumask_t non_isolated_cpus;



	lock_cpu_hotplug();

	mutex_lock(&sched_hotcpu_mutex);

	arch_init_sched_domains(&cpu_online_map);

	cpus_andnot(non_isolated_cpus, cpu_possible_map, cpu_isolated_map);

	if (cpus_empty(non_isolated_cpus))

		cpu_set(smp_processor_id(), non_isolated_cpus);

	unlock_cpu_hotplug();

	mutex_unlock(&sched_hotcpu_mutex);

	/* XXX: Theoretical race here - CPU may be hotplugged now */

	hotcpu_notifier(update_sched_domains, 0);