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kthread: Implement park/unpark facility
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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 <[email protected]>
Reviewed-by: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Reviewed-by: Srivatsa S. Bhat <[email protected]>
Cc: Rusty Russell <[email protected]>
Reviewed-by: Paul E. McKenney <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>
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@KAGA-KOKO
KAGA-KOKO committed Aug 13, 2012
1 parent 5d01bbd commit 2a1d446
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Showing 2 changed files with 176 additions and 20 deletions.
11 changes: 10 additions & 1 deletion include/linux/kthread.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,11 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
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).
Expand All @@ -34,9 +39,13 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),

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;
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185 changes: 166 additions & 19 deletions kernel/kthread.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)

Expand All @@ -52,12 +61,28 @@ 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 park now?
*
* When someone calls kthread_park() on your kthread, it will be woken
* and this will return true. You should then do the necessary
* cleanup and call kthread_parkme()
*
* Similar to kthread_should_stop(), but this keeps the thread alive
* and in a park position. kthread_unpark() "restarts" 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
Expand Down Expand Up @@ -96,6 +121,24 @@ void *kthread_data(struct task_struct *task)
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();
__set_current_state(TASK_INTERRUPTIBLE);
}
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 */
Expand All @@ -105,9 +148,10 @@ 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 */
Expand All @@ -117,9 +161,11 @@ 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);
}
Expand Down Expand Up @@ -172,8 +218,7 @@ static void create_kthread(struct kthread_create_info *create)
* 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[],
...)
{
Expand Down Expand Up @@ -210,6 +255,13 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
}
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().
Expand All @@ -226,13 +278,111 @@ void kthread_bind(struct task_struct *p, unsigned int cpu)
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.
* @cpu: The cpu on which the thread should be bound,
* @namefmt: printf-style name for the thread. Format is restricted
* to "name.*%u". Code fills in cpu number.
*
* Description: This helper function creates and names a kernel thread
* 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;
set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
to_kthread(p)->cpu = cpu;
/* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
kthread_park(p);
return p;
}

static struct kthread *task_get_live_kthread(struct task_struct *k)
{
struct kthread *kthread;

get_task_struct(k);
kthread = to_kthread(k);
/* It might have exited */
barrier();
if (k->vfork_done != NULL)
return kthread;
return NULL;
}

/**
* 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 = task_get_live_kthread(k);

if (kthread) {
clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
/*
* We clear the IS_PARKED bit here as we don't wait
* until the task has left the park code. So if we'd
* park before that happens we'd see the IS_PARKED bit
* which might be about to be cleared.
*/
if (test_and_clear_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 = task_get_live_kthread(k);
int ret = -ENOSYS;

if (kthread) {
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().
Expand All @@ -250,16 +400,13 @@ EXPORT_SYMBOL(kthread_bind);
*/
int kthread_stop(struct task_struct *k)
{
struct kthread *kthread;
struct kthread *kthread = task_get_live_kthread(k);
int ret;

trace_sched_kthread_stop(k);
get_task_struct(k);

kthread = to_kthread(k);
barrier(); /* it might have exited */
if (k->vfork_done != NULL) {
kthread->should_stop = 1;
if (kthread) {
set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
wake_up_process(k);
wait_for_completion(&kthread->exited);
}
Expand Down

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