[RFC patch 1/5] kthread: Implement park/unpark facility

Thomas Gleixner
2012-06-13T11:01:34Z

[-- Attachment #1: kthread-implement-park-and-percpu.patch --]
[-- Type: text/plain, Size: 8515 bytes --]

To avoid the full teardown/setup of per cpu kthreads in the case of
cpu hot(un)plug, provide a facility which allows to put the kthread
into a park position and unpark it when the cpu comes online again.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/kthread.h | 11 ++-
kernel/kthread.c | 165 ++++++++++++++++++++++++++++++++++++++++++++----
2 files changed, 162 insertions(+), 14 deletions(-)

Index: tip/include/linux/kthread.h
===================================================================
--- tip.orig/include/linux/kthread.h
+++ tip/include/linux/kthread.h
@@ -14,6 +14,11 @@ struct task_struct *kthread_create_on_no
kthread_create_on_node(threadfn, data, -1, namefmt, ##arg)

+struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
+ void *data,
+ unsigned int cpu,
+ const char *namefmt);
+
/**
* kthread_run - create and wake a thread.
* @threadfn: the function to run until signal_pending(current).
@@ -34,9 +39,13 @@ struct task_struct *kthread_create_on_no

void kthread_bind(struct task_struct *k, unsigned int cpu);
int kthread_stop(struct task_struct *k);
-int kthread_should_stop(void);
+bool kthread_should_stop(void);
+bool kthread_should_park(void);
bool kthread_freezable_should_stop(bool *was_frozen);
void *kthread_data(struct task_struct *k);
+int kthread_park(struct task_struct *k);
+void kthread_unpark(struct task_struct *k);
+void kthread_parkme(void);

int kthreadd(void *unused);
extern struct task_struct *kthreadd_task;
Index: tip/kernel/kthread.c
===================================================================
--- tip.orig/kernel/kthread.c
+++ tip/kernel/kthread.c
@@ -37,11 +37,20 @@ struct kthread_create_info
};

struct kthread {
- int should_stop;
+ unsigned long flags;
+ unsigned int cpu;
void *data;
+ struct completion parked;
struct completion exited;
};

+enum KTHREAD_BITS {
+ KTHREAD_IS_PER_CPU = 0,
+ KTHREAD_SHOULD_STOP,
+ KTHREAD_SHOULD_PARK,
+ KTHREAD_IS_PARKED,
+};
+
#define to_kthread(tsk) \
container_of((tsk)->vfork_done, struct kthread, exited)

@@ -52,13 +61,29 @@ struct kthread {
* and this will return true. You should then return, and your return
* value will be passed through to kthread_stop().
*/
-int kthread_should_stop(void)
+bool kthread_should_stop(void)
{
- return to_kthread(current)->should_stop;
+ return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
}
EXPORT_SYMBOL(kthread_should_stop);

/**
+ * kthread_should_park - should this kthread return now?
+ *
+ * When someone calls kthread_park() on your kthread, it will be woken
+ * and this will return true. You should then return, and your return
+ * value will be passed through to kthread_park().
+ *
+ * Similar to kthread_should_stop(), but this keeps the thread alive
+ * and in a park position. kthread_unpark() "restart" the thread and
+ * calls the thread function again.
+ */
+bool kthread_should_park(void)
+{
+ return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags);
+}
+
+/**
* kthread_freezable_should_stop - should this freezable kthread return now?
* @was_frozen: optional out parameter, indicates whether %current was frozen
*
@@ -96,6 +121,23 @@ void *kthread_data(struct task_struct *t
return to_kthread(task)->data;
}

+static void __kthread_parkme(struct kthread *self)
+{
+ __set_current_state(TASK_INTERRUPTIBLE);
+ while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
+ if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
+ complete(&self->parked);
+ schedule();
+ }
+ clear_bit(KTHREAD_IS_PARKED, &self->flags);
+ __set_current_state(TASK_RUNNING);
+}
+
+void kthread_parkme(void)
+{
+ __kthread_parkme(to_kthread(current));
+}
+
static int kthread(void *_create)
{
/* Copy data: it's on kthread's stack */
@@ -105,9 +147,10 @@ static int kthread(void *_create)
struct kthread self;
int ret;

- self.should_stop = 0;
+ self.flags = 0;
self.data = data;
init_completion(&self.exited);
+ init_completion(&self.parked);
current->vfork_done = &self.exited;

/* OK, tell user we're spawned, wait for stop or wakeup */
@@ -117,9 +160,11 @@ static int kthread(void *_create)
schedule();

ret = -EINTR;
- if (!self.should_stop)
- ret = threadfn(data);

+ if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
+ __kthread_parkme(&self);
+ ret = threadfn(data);
+ }
/* we can't just return, we must preserve "self" on stack */
do_exit(ret);
}
@@ -172,8 +217,7 @@ static void create_kthread(struct kthrea
* Returns a task_struct or ERR_PTR(-ENOMEM).
*/
struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
- void *data,
- int node,
+ void *data, int node,
const char namefmt[],
...)
{
@@ -210,6 +254,13 @@ struct task_struct *kthread_create_on_no
}
EXPORT_SYMBOL(kthread_create_on_node);

+static void __kthread_bind(struct task_struct *p, unsigned int cpu)
+{
+ /* It's safe because the task is inactive. */
+ do_set_cpus_allowed(p, cpumask_of(cpu));
+ p->flags |= PF_THREAD_BOUND;
+}
+
/**
* kthread_bind - bind a just-created kthread to a cpu.
* @p: thread created by kthread_create().
@@ -226,14 +277,102 @@ void kthread_bind(struct task_struct *p,
WARN_ON(1);
return;
}
-
- /* It's safe because the task is inactive. */
- do_set_cpus_allowed(p, cpumask_of(cpu));
- p->flags |= PF_THREAD_BOUND;
+ __kthread_bind(p, cpu);
}
EXPORT_SYMBOL(kthread_bind);

/**
+ * kthread_create_on_cpu - Create a cpu bound kthread
+ * @threadfn: the function to run until signal_pending(current).
+ * @data: data ptr for @threadfn.
+ * @node: memory node number.
+ * @namefmt: printf-style name for the thread.
+ *
+ * Description: This helper function creates and names a kernel thread
+ * and binds it to a given CPU. The thread will be woken and put into
+ * park mode.
+ */
+struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
+ void *data, unsigned int cpu,
+ const char *namefmt)
+{
+ struct task_struct *p;
+
+ p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
+ cpu);
+ if (IS_ERR(p))
+ return p;
+ /* Park the thread, mark it percpu and then bind it */
+ kthread_park(p);
+ set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
+ to_kthread(p)->cpu = cpu;
+ __kthread_bind(p, cpu);
+ return p;
+}
+
+/**
+ * kthread_unpark - unpark a thread created by kthread_create().
+ * @k: thread created by kthread_create().
+ *
+ * Sets kthread_should_park() for @k to return false, wakes it, and
+ * waits for it to return. If the thread is marked percpu then its
+ * bound to the cpu again.
+ */
+void kthread_unpark(struct task_struct *k)
+{
+ struct kthread *kthread;
+
+ get_task_struct(k);
+
+ kthread = to_kthread(k);
+ barrier(); /* it might have exited */
+ if (k->vfork_done != NULL) {
+ clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+ if (test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
+ if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
+ __kthread_bind(k, kthread->cpu);
+ wake_up_process(k);
+ }
+ }
+ put_task_struct(k);
+}
+
+/**
+ * kthread_park - park a thread created by kthread_create().
+ * @k: thread created by kthread_create().
+ *
+ * Sets kthread_should_park() for @k to return true, wakes it, and
+ * waits for it to return. This can also be called after kthread_create()
+ * instead of calling wake_up_process(): the thread will park without
+ * calling threadfn().
+ *
+ * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
+ * If called by the kthread itself just the park bit is set.
+ */
+int kthread_park(struct task_struct *k)
+{
+ struct kthread *kthread;
+ int ret = -ENOSYS;
+
+ get_task_struct(k);
+
+ kthread = to_kthread(k);
+ barrier(); /* it might have exited */
+ if (k->vfork_done != NULL) {
+ if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
+ set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
+ if (k != current) {
+ wake_up_process(k);
+ wait_for_completion(&kthread->parked);
+ }
+ }
+ ret = 0;
+ }
+ put_task_struct(k);
+ return ret;
+}
+
+/**
* kthread_stop - stop a thread created by kthread_create().
* @k: thread created by kthread_create().
*
@@ -259,7 +398,7 @@ int kthread_stop(struct task_struct *k)
kthread = to_kthread(k);
barrier(); /* it might have exited */
if (k->vfork_done != NULL) {
- kthread->should_stop = 1;
+ set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
wake_up_process(k);
wait_for_completion(&kthread->exited);
}