Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 6a1bdc1b authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

sched: _cpu_down(): Don't play with current->cpus_allowed 



_cpu_down() changes the current task's affinity and then recovers it at
the end. The problems are well known: we can't restore old_allowed if it
was bound to the now-dead-cpu, and we can race with the userspace which
can change cpu-affinity during unplug.

_cpu_down() should not play with current->cpus_allowed at all. Instead,
take_cpu_down() can migrate the caller of _cpu_down() after __cpu_disable()
removes the dying cpu from cpu_online_mask.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100315091023.GA9148@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 30da688e

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1843,6 +1843,7 @@ extern void sched_clock_idle_sleep_event(void); 
extern void sched_clock_idle_wakeup_event(u64 delta_ns);



#ifdef CONFIG_HOTPLUG_CPU

extern void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p);

extern void idle_task_exit(void);

#else

static inline void idle_task_exit(void) {}

kernel/cpu.c

+6 −12
Original line number Diff line number Diff line
@@ -163,6 +163,7 @@ static inline void check_for_tasks(int cpu) 
}



struct take_cpu_down_param {

	struct task_struct *caller;

	unsigned long mod;

	void *hcpu;

};
@@ -171,6 +172,7 @@ struct take_cpu_down_param { 
static int __ref take_cpu_down(void *_param)

{

	struct take_cpu_down_param *param = _param;

	unsigned int cpu = (unsigned long)param->hcpu;

	int err;



	/* Ensure this CPU doesn't handle any more interrupts. */
@@ -181,6 +183,8 @@ static int __ref take_cpu_down(void *_param) 
	raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,

				param->hcpu);



	if (task_cpu(param->caller) == cpu)

		move_task_off_dead_cpu(cpu, param->caller);

	/* Force idle task to run as soon as we yield: it should

	   immediately notice cpu is offline and die quickly. */

	sched_idle_next();
@@ -191,10 +195,10 @@ static int __ref take_cpu_down(void *_param) 
static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)

{

	int err, nr_calls = 0;

	cpumask_var_t old_allowed;

	void *hcpu = (void *)(long)cpu;

	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;

	struct take_cpu_down_param tcd_param = {

		.caller = current,

		.mod = mod,

		.hcpu = hcpu,

	};
@@ -205,9 +209,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) 
	if (!cpu_online(cpu))

		return -EINVAL;



	if (!alloc_cpumask_var(&old_allowed, GFP_KERNEL))

		return -ENOMEM;



	cpu_hotplug_begin();

	set_cpu_active(cpu, false);

	err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
@@ -224,10 +225,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) 
		goto out_release;

	}



	/* Ensure that we are not runnable on dying cpu */

	cpumask_copy(old_allowed, &current->cpus_allowed);

	set_cpus_allowed_ptr(current, cpu_active_mask);



	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));

	if (err) {

		set_cpu_active(cpu, true);
@@ -236,7 +233,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) 
					    hcpu) == NOTIFY_BAD)

			BUG();



		goto out_allowed;

		goto out_release;

	}

	BUG_ON(cpu_online(cpu));
@@ -254,8 +251,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) 


	check_for_tasks(cpu);



out_allowed:

	set_cpus_allowed_ptr(current, old_allowed);

out_release:

	cpu_hotplug_done();

	if (!err) {
@@ -263,7 +258,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) 
					    hcpu) == NOTIFY_BAD)

			BUG();

	}

	free_cpumask_var(old_allowed);

	return err;

}

kernel/sched.c

+1 −1
Original line number Diff line number Diff line
@@ -5442,7 +5442,7 @@ static int migration_thread(void *data) 
/*

 * Figure out where task on dead CPU should go, use force if necessary.

 */

static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)

void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)

{

	struct rq *rq = cpu_rq(dead_cpu);

	int needs_cpu, uninitialized_var(dest_cpu);