| From 4975da0b15e3f087b00c8b2e8a15b95161c3cb90 Mon Sep 17 00:00:00 2001 |
| From: Oleg Nesterov <oleg@redhat.com> |
| Date: Mon, 15 Mar 2010 10:10:23 +0100 |
| Subject: [PATCH] sched: _cpu_down(): Don't play with current->cpus_allowed |
| |
| commit bb8eef78087fd2f10bcfca68f794640f7d37592c in tip. |
| |
| _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. |
| |
| [ upstream commit: 6a1bdc1b577ebcb65f6603c57f8347309bc4ab13 ] |
| |
| 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> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| |
| diff --git a/include/linux/sched.h b/include/linux/sched.h |
| index 18ae27a..01d8b97 100644 |
| --- a/include/linux/sched.h |
| +++ b/include/linux/sched.h |
| @@ -2032,6 +2032,7 @@ 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) {} |
| diff --git a/kernel/cpu.c b/kernel/cpu.c |
| index 677f253..48b916e 100644 |
| --- a/kernel/cpu.c |
| +++ b/kernel/cpu.c |
| @@ -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, ¤t->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 @@ out_release: |
| hcpu) == NOTIFY_BAD) |
| BUG(); |
| } |
| - free_cpumask_var(old_allowed); |
| return err; |
| } |
| |
| diff --git a/kernel/sched.c b/kernel/sched.c |
| index adad328..c38298d 100644 |
| --- a/kernel/sched.c |
| +++ b/kernel/sched.c |
| @@ -7706,7 +7706,7 @@ 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); |
| -- |
| 1.7.1.1 |
| |