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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: Oleg Nesterov <oleg@redhat.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100315091023.GA9148@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Oleg Nesterov 2010-03-15 10:10:23 +01:00 committed by Ingo Molnar
parent 30da688ef6
commit 6a1bdc1b57
3 changed files with 8 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/sched.h
View File

@ -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) {}

18
kernel/cpu.c
View File

@ -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;
}

2
kernel/sched.c
View File

@ -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);