The patch titled
cpu_hotplug: don't affect current task's affinity
has been removed from the -mm tree. Its filename was
cpu_hotplug-dont-affect-current-tasks-affinity.patch
This patch was dropped because it is obsolete
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: cpu_hotplug: don't affect current task's affinity
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
_cpu_down() changes the current task's affinity and then recovers it at
the end.
It has two problems:
1) The recovery of the current tasks's cpus_allowed will fail under
some conditions.
# grep Cpus_allowed_list /proc/$$/status
Cpus_allowed_list: 0-3
# taskset -pc 2 $$
pid 29075's current affinity list: 0-3
pid 29075's new affinity list: 2
# grep Cpus_allowed_list /proc/$$/status
Cpus_allowed_list: 2
# echo 0 > /sys/devices/system/cpu/cpu2/online
# grep Cpus_allowed_list /proc/$$/status
Cpus_allowed_list: 0
Here, the Cpus_allowed_list was originally "2" and has become
"0-1,3" after cpu #2 is offlined.
This "Cpus_allowed_list: 0" is incorrect.
2) If the current task is a userspace task, the user may change its
cpu-affinity during the CPU hot-unplugging. This change can be
overwritten when _cpu_down() changes the current task's affinity.
Fix all this by not changing the current tasks's affinity. Instead we
create a kernel thread to do the work.
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/cpu.c | 72 ++++++++++++++++++++++++++++---------------------
1 file changed, 42 insertions(+), 30 deletions(-)
diff -puN kernel/cpu.c~cpu_hotplug-dont-affect-current-tasks-affinity kernel/cpu.c
--- a/kernel/cpu.c~cpu_hotplug-dont-affect-current-tasks-affinity
+++ a/kernel/cpu.c
@@ -162,15 +162,17 @@ static inline void check_for_tasks(int c
write_unlock_irq(&tasklist_lock);
}
-struct take_cpu_down_param {
+struct cpu_down_param {
unsigned long mod;
- void *hcpu;
+ unsigned int cpu;
+ int ret;
+ struct completion done;
};
/* Take this CPU down. */
static int __ref take_cpu_down(void *_param)
{
- struct take_cpu_down_param *param = _param;
+ struct cpu_down_param *param = _param;
int err;
/* Ensure this CPU doesn't handle any more interrupts. */
@@ -179,7 +181,7 @@ static int __ref take_cpu_down(void *_pa
return err;
raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
- param->hcpu);
+ (void *)(long)param->cpu);
/* Force idle task to run as soon as we yield: it should
immediately notice cpu is offline and die quickly. */
@@ -187,26 +189,13 @@ static int __ref take_cpu_down(void *_pa
return 0;
}
-/* Requires cpu_add_remove_lock to be held */
-static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
+static int __ref _cpu_down_thread(void *_param)
{
+ struct cpu_down_param *param = _param;
int err, nr_calls = 0;
- cpumask_var_t old_allowed;
+ unsigned long mod = param->mod;
+ unsigned int cpu = param->cpu;
void *hcpu = (void *)(long)cpu;
- unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
- struct take_cpu_down_param tcd_param = {
- .mod = mod,
- .hcpu = hcpu,
- };
-
- if (num_online_cpus() == 1)
- return -EBUSY;
-
- if (!cpu_online(cpu))
- return -EINVAL;
-
- if (!alloc_cpumask_var(&old_allowed, GFP_KERNEL))
- return -ENOMEM;
cpu_hotplug_begin();
err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
@@ -222,18 +211,16 @@ static int __ref _cpu_down(unsigned int
}
/* Ensure that we are not runnable on dying cpu */
- cpumask_copy(old_allowed, ¤t->cpus_allowed);
- set_cpus_allowed_ptr(current,
- cpumask_of(cpumask_any_but(cpu_online_mask, cpu)));
+ set_cpus_allowed_ptr(current, cpu_active_mask);
- err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
+ err = __stop_machine(take_cpu_down, param, cpumask_of(cpu));
if (err) {
/* CPU didn't die: tell everyone. Can't complain. */
if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
hcpu) == NOTIFY_BAD)
BUG();
- goto out_allowed;
+ goto out_release;
}
BUG_ON(cpu_online(cpu));
@@ -251,8 +238,6 @@ static int __ref _cpu_down(unsigned int
check_for_tasks(cpu);
-out_allowed:
- set_cpus_allowed_ptr(current, old_allowed);
out_release:
cpu_hotplug_done();
if (!err) {
@@ -260,8 +245,35 @@ out_release:
hcpu) == NOTIFY_BAD)
BUG();
}
- free_cpumask_var(old_allowed);
- return err;
+ param->ret = err;
+ complete(¶m->done);
+
+ return 0;
+}
+
+/* Requires cpu_add_remove_lock to be held */
+static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
+{
+ struct task_struct *k;
+ struct cpu_down_param param = {
+ .mod = tasks_frozen ? CPU_TASKS_FROZEN : 0,
+ .cpu = cpu,
+ .ret = 0,
+ };
+
+ if (num_online_cpus() == 1)
+ return -EBUSY;
+
+ if (!cpu_online(cpu))
+ return -EINVAL;
+
+ init_completion(¶m.done);
+ k = kthread_run(_cpu_down_thread, ¶m, "kcpu_down");
+ if (IS_ERR(k))
+ return PTR_ERR(k);
+ wait_for_completion(¶m.done);
+
+ return param.ret;
}
int __ref cpu_down(unsigned int cpu)
_
Patches currently in -mm which might be from laijs@xxxxxxxxxxxxxx are
linux-next.patch
cpu_hotplug-dont-affect-current-tasks-affinity.patch
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