path: root/kernel/kthread.c

// SPDX-License-Identifier: GPL-2.0-only
/* Kernel thread helper functions.
 *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
 *   Copyright (C) 2009 Red Hat, Inc.
 *
 * Creation is done via kthreadd, so that we get a clean environment
 * even if we're invoked from userspace (think modprobe, hotplug cpu,
 * etc.).
 */
#include <uapi/linux/sched/types.h>
#include <linux/mm.h>
#include <linux/mmu_context.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/sched/task.h>
#include <linux/kthread.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/cgroup.h>
#include <linux/cpuset.h>
#include <linux/unistd.h>
#include <linux/file.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/freezer.h>
#include <linux/ptrace.h>
#include <linux/uaccess.h>
#include <linux/numa.h>
#include <linux/sched/isolation.h>
#include <trace/events/sched.h>


static DEFINE_SPINLOCK(kthread_create_lock);
static LIST_HEAD(kthread_create_list);
struct task_struct *kthreadd_task;

struct kthread_create_info
{
	/* Information passed to kthread() from kthreadd. */
	char *full_name;
	int (*threadfn)(void *data);
	void *data;
	int node;

	/* Result passed back to kthread_create() from kthreadd. */
	struct task_struct *result;
	struct completion *done;

	struct list_head list;
};

struct kthread {
	unsigned long flags;
	unsigned int cpu;
	int result;
	int (*threadfn)(void *);
	void *data;
	struct completion parked;
	struct completion exited;
#ifdef CONFIG_BLK_CGROUP
	struct cgroup_subsys_state *blkcg_css;
#endif
	/* To store the full name if task comm is truncated. */
	char *full_name;
};

enum KTHREAD_BITS {
	KTHREAD_IS_PER_CPU = 0,
	KTHREAD_SHOULD_STOP,
	KTHREAD_SHOULD_PARK,
};

static inline struct kthread *to_kthread(struct task_struct *k)
{
	WARN_ON(!(k->flags & PF_KTHREAD));
	return k->worker_private;
}

/*
 * Variant of to_kthread() that doesn't assume @p is a kthread.
 *
 * Per construction; when:
 *
 *   (p->flags & PF_KTHREAD) && p->worker_private
 *
 * the task is both a kthread and struct kthread is persistent. However
 * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
 * begin_new_exec()).
 */
static inline struct kthread *__to_kthread(struct task_struct *p)
{
	void *kthread = p->worker_private;
	if (kthread && !(p->flags & PF_KTHREAD))
		kthread = NULL;
	return kthread;
}

void get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk)
{
	struct kthread *kthread = to_kthread(tsk);

	if (!kthread || !kthread->full_name) {
		__get_task_comm(buf, buf_size, tsk);
		return;
	}

	strscpy_pad(buf, kthread->full_name, buf_size);
}

bool set_kthread_struct(struct task_struct *p)
{
	struct kthread *kthread;

	if (WARN_ON_ONCE(to_kthread(p)))
		return false;

	kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
	if (!kthread)
		return false;

	init_completion(&kthread->exited);
	init_completion(&kthread->parked);
	p->vfork_done = &kthread->exited;

	p->worker_private = kthread;
	return true;
}

void free_kthread_struct(struct task_struct *k)
{
	struct kthread *kthread;

	/*
	 * Can be NULL if kmalloc() in set_kthread_struct() failed.
	 */
	kthread = to_kthread(k);
	if (!kthread)
		return;

#ifdef CONFIG_BLK_CGROUP
	WARN_ON_ONCE(kthread->blkcg_css);
#endif
	k->worker_private = NULL;
	kfree(kthread->full_name);
	kfree(kthread);
}

/**
 * kthread_should_stop - should this kthread return now?
 *
 * When someone calls kthread_stop() 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_stop().
 */
bool kthread_should_stop(void)
{
	return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
}
EXPORT_SYMBOL(kthread_should_stop);

static bool __kthread_should_park(struct task_struct *k)
{
	return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(k)->flags);
}

/**
 * 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 __kthread_should_park(current);
}
EXPORT_SYMBOL_GPL(kthread_should_park);

bool kthread_should_stop_or_park(void)
{
	struct kthread *kthread = __to_kthread(current);

	if (!kthread)
		return false;

	return kthread->flags & (BIT(KTHREAD_SHOULD_STOP) | BIT(KTHREAD_SHOULD_PARK));
}

/**
 * kthread_freezable_should_stop - should this freezable kthread return now?
 * @was_frozen: optional out parameter, indicates whether %current was frozen
 *
 * kthread_should_stop() for freezable kthreads, which will enter
 * refrigerator if necessary.  This function is safe from kthread_stop() /
 * freezer deadlock and freezable kthreads should use this function instead
 * of calling try_to_freeze() directly.
 */
bool kthread_freezable_should_stop(bool *was_frozen)
{
	bool frozen = false;

	might_sleep();

	if (unlikely(freezing(current)))
		frozen = __refrigerator(true);

	if (was_frozen)
		*was_frozen = frozen;

	return kthread_should_stop();
}
EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);

/**
 * kthread_func - return the function specified on kthread creation
 * @task: kthread task in question
 *
 * Returns NULL if the task is not a kthread.
 */
void *kthread_func(struct task_struct *task)
{
	struct kthread *kthread = __to_kthread(task);
	if (kthread)
		return kthread->threadfn;
	return NULL;
}
EXPORT_SYMBOL_GPL(kthread_func);

/**
 * kthread_data - return data value specified on kthread creation
 * @task: kthread task in question
 *
 * Return the data value specified when kthread @task was created.
 * The caller is responsible for ensuring the validity of @task when
 * calling this function.
 */
void *kthread_data(struct task_struct *task)
{
	return to_kthread(task)->data;
}
EXPORT_SYMBOL_GPL(kthread_data);

/**
 * kthread_probe_data - speculative version of kthread_data()
 * @task: possible kthread task in question
 *
 * @task could be a kthread task.  Return the data value specified when it
 * was created if accessible.  If @task isn't a kthread task or its data is
 * inaccessible for any reason, %NULL is returned.  This function requires
 * that @task itself is safe to dereference.
 */
void *kthread_probe_data(struct task_struct *task)
{
	struct kthread *kthread = __to_kthread(task);
	void *data = NULL;

	if (kthread)
		copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
	return data;
}

static void __kthread_parkme(struct kthread *self)
{
	for (;;) {
		/*
		 * TASK_PARKED is a special state; we must serialize against
		 * possible pending wakeups to avoid store-store collisions on
		 * task->state.
		 *
		 * Such a collision might possibly result in the ta