linux/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
{ … };

struct kthread { … };

enum KTHREAD_BITS { … };

static inline struct kthread *to_kthread(struct task_struct *k)
{ … }

/*
 * 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 get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk)
{ … }

bool set_kthread_struct(struct task_struct *p)
{ … }

void free_kthread_struct(struct task_struct *k)
{ … }

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

static bool __kthread_should_park(struct task_struct *k)
{ … }

/**
 * 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)
{ … }
EXPORT_SYMBOL_GPL(…);

bool kthread_should_stop_or_park(void)
{ … }

/**
 * 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)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * 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)
{ … }

static void __kthread_parkme(struct kthread *self)
{ … }

void kthread_parkme(void)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * kthread_exit - Cause the current kthread return @result to kthread_stop().
 * @result: The integer value to return to kthread_stop().
 *
 * While kthread_exit can be called directly, it exists so that
 * functions which do some additional work in non-modular code such as
 * module_put_and_kthread_exit can be implemented.
 *
 * Does not return.
 */
void __noreturn kthread_exit(long result)
{ … }
EXPORT_SYMBOL(…);

/**
 * kthread_complete_and_exit - Exit the current kthread.
 * @comp: Completion to complete
 * @code: The integer value to return to kthread_stop().
 *
 * If present, complete @comp and then return code to kthread_stop().
 *
 * A kernel thread whose module may be removed after the completion of
 * @comp can use this function to exit safely.
 *
 * Does not return.
 */
void __noreturn kthread_complete_and_exit(struct completion *comp, long code)
{ … }
EXPORT_SYMBOL(…);

static int kthread(void *_create)
{ … }

/* called from kernel_clone() to get node information for about to be created task */
int tsk_fork_get_node(struct task_struct *tsk)
{ … }

static void create_kthread(struct kthread_create_info *create)
{ … }

static __printf(4, 0)
struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
						    void *data, int node,
						    const char namefmt[],
						    va_list args)
{ … }

/**
 * kthread_create_on_node - create a kthread.
 * @threadfn: the function to run until signal_pending(current).
 * @data: data ptr for @threadfn.
 * @node: task and thread structures for the thread are allocated on this node
 * @namefmt: printf-style name for the thread.
 *
 * Description: This helper function creates and names a kernel
 * thread.  The thread will be stopped: use wake_up_process() to start
 * it.  See also kthread_run().  The new thread has SCHED_NORMAL policy and
 * is affine to all CPUs.
 *
 * If thread is going to be bound on a particular cpu, give its node
 * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
 * When woken, the thread will run @threadfn() with @data as its
 * argument. @threadfn() can either return directly if it is a
 * standalone thread for which no one will call kthread_stop(), or
 * return when 'kthread_should_stop()' is true (which means
 * kthread_stop() has been called).  The return value should be zero
 * or a negative error number; it will be passed to kthread_stop().
 *
 * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
 */
struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
					   void *data, int node,
					   const char namefmt[],
					   ...)
{ … }
EXPORT_SYMBOL(…);

static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, unsigned int state)
{ … }

static void __kthread_bind(struct task_struct *p, unsigned int cpu, unsigned int state)
{ … }

void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
{ … }

/**
 * kthread_bind - bind a just-created kthread to a cpu.
 * @p: thread created by kthread_create().
 * @cpu: cpu (might not be online, must be possible) for @k to run on.
 *
 * Description: This function is equivalent to set_cpus_allowed(),
 * except that @cpu doesn't need to be online, and the thread must be
 * stopped (i.e., just returned from kthread_create()).
 */
void kthread_bind(struct task_struct *p, unsigned int cpu)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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
 */
struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
					  void *data, unsigned int cpu,
					  const char *namefmt)
{ … }
EXPORT_SYMBOL(…);

void kthread_set_per_cpu(struct task_struct *k, int cpu)
{ … }

bool kthread_is_per_cpu(struct task_struct *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)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * kthread_stop - stop a thread created by kthread_create().
 * @k: thread created by kthread_create().
 *
 * Sets kthread_should_stop() for @k to return true, wakes it, and
 * waits for it to exit. This can also be called after kthread_create()
 * instead of calling wake_up_process(): the thread will exit without
 * calling threadfn().
 *
 * If threadfn() may call kthread_exit() itself, the caller must ensure
 * task_struct can't go away.
 *
 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 * was never called.
 */
int kthread_stop(struct task_struct *k)
{ … }
EXPORT_SYMBOL(…);

/**
 * kthread_stop_put - stop a thread and put its task struct
 * @k: thread created by kthread_create().
 *
 * Stops a thread created by kthread_create() and put its task_struct.
 * Only use when holding an extra task struct reference obtained by
 * calling get_task_struct().
 */
int kthread_stop_put(struct task_struct *k)
{ … }
EXPORT_SYMBOL(…);

int kthreadd(void *unused)
{ … }

void __kthread_init_worker(struct kthread_worker *worker,
				const char *name,
				struct lock_class_key *key)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * kthread_worker_fn - kthread function to process kthread_worker
 * @worker_ptr: pointer to initialized kthread_worker
 *
 * This function implements the main cycle of kthread worker. It processes
 * work_list until it is stopped with kthread_stop(). It sleeps when the queue
 * is empty.
 *
 * The works are not allowed to keep any locks, disable preemption or interrupts
 * when they finish. There is defined a safe point for freezing when one work
 * finishes and before a new one is started.
 *
 * Also the works must not be handled by more than one worker at the same time,
 * see also kthread_queue_work().
 */
int kthread_worker_fn(void *worker_ptr)
{ … }
EXPORT_SYMBOL_GPL(…);

static __printf(3, 0) struct kthread_worker *
__kthread_create_worker(int cpu, unsigned int flags,
			const char namefmt[], va_list args)
{ … }

/**
 * kthread_create_worker - create a kthread worker
 * @flags: flags modifying the default behavior of the worker
 * @namefmt: printf-style name for the kthread worker (task).
 *
 * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
 * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
 * when the caller was killed by a fatal signal.
 */
struct kthread_worker *
kthread_create_worker(unsigned int flags, const char namefmt[], ...)
{ … }
EXPORT_SYMBOL(…);

/**
 * kthread_create_worker_on_cpu - create a kthread worker and bind it
 *	to a given CPU and the associated NUMA node.
 * @cpu: CPU number
 * @flags: flags modifying the default behavior of the worker
 * @namefmt: printf-style name for the kthread worker (task).
 *
 * Use a valid CPU number if you want to bind the kthread worker
 * to the given CPU and the associated NUMA node.
 *
 * A good practice is to add the cpu number also into the worker name.
 * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
 *
 * CPU hotplug:
 * The kthread worker API is simple and generic. It just provides a way
 * to create, use, and destroy workers.
 *
 * It is up to the API user how to handle CPU hotplug. They have to decide
 * how to handle pending work items, prevent queuing new ones, and
 * restore the functionality when the CPU goes off and on. There are a
 * few catches:
 *
 *    - CPU affinity gets lost when it is scheduled on an offline CPU.
 *
 *    - The worker might not exist when the CPU was off when the user
 *      created the workers.
 *
 * Good practice is to implement two CPU hotplug callbacks and to
 * destroy/create the worker when the CPU goes down/up.
 *
 * Return:
 * The pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
 * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
 * when the caller was killed by a fatal signal.
 */
struct kthread_worker *
kthread_create_worker_on_cpu(int cpu, unsigned int flags,
			     const char namefmt[], ...)
{ … }
EXPORT_SYMBOL(…);

/*
 * Returns true when the work could not be queued at the moment.
 * It happens when it is already pending in a worker list
 * or when it is being cancelled.
 */
static inline bool queuing_blocked(struct kthread_worker *worker,
				   struct kthread_work *work)
{ … }

static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
					     struct kthread_work *work)
{ … }

/* insert @work before @pos in @worker */
static void kthread_insert_work(struct kthread_worker *worker,
				struct kthread_work *work,
				struct list_head *pos)
{ … }

/**
 * kthread_queue_work - queue a kthread_work
 * @worker: target kthread_worker
 * @work: kthread_work to queue
 *
 * Queue @work to work processor @task for async execution.  @task
 * must have been created with kthread_worker_create().  Returns %true
 * if @work was successfully queued, %false if it was already pending.
 *
 * Reinitialize the work if it needs to be used by another worker.
 * For example, when the worker was stopped and started again.
 */
bool kthread_queue_work(struct kthread_worker *worker,
			struct kthread_work *work)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * kthread_delayed_work_timer_fn - callback that queues the associated kthread
 *	delayed work when the timer expires.
 * @t: pointer to the expired timer
 *
 * The format of the function is defined by struct timer_list.
 * It should have been called from irqsafe timer with irq already off.
 */
void kthread_delayed_work_timer_fn(struct timer_list *t)
{ … }
EXPORT_SYMBOL(…);

static void __kthread_queue_delayed_work(struct kthread_worker *worker,
					 struct kthread_delayed_work *dwork,
					 unsigned long delay)
{ … }

/**
 * kthread_queue_delayed_work - queue the associated kthread work
 *	after a delay.
 * @worker: target kthread_worker
 * @dwork: kthread_delayed_work to queue
 * @delay: number of jiffies to wait before queuing
 *
 * If the work has not been pending it starts a timer that will queue
 * the work after the given @delay. If @delay is zero, it queues the
 * work immediately.
 *
 * Return: %false if the @work has already been pending. It means that
 * either the timer was running or the work was queued. It returns %true
 * otherwise.
 */
bool kthread_queue_delayed_work(struct kthread_worker *worker,
				struct kthread_delayed_work *dwork,
				unsigned long delay)
{ … }
EXPORT_SYMBOL_GPL(…);

struct kthread_flush_work { … };

static void kthread_flush_work_fn(struct kthread_work *work)
{ … }

/**
 * kthread_flush_work - flush a kthread_work
 * @work: work to flush
 *
 * If @work is queued or executing, wait for it to finish execution.
 */
void kthread_flush_work(struct kthread_work *work)
{ … }
EXPORT_SYMBOL_GPL(…);

/*
 * Make sure that the timer is neither set nor running and could
 * not manipulate the work list_head any longer.
 *
 * The function is called under worker->lock. The lock is temporary
 * released but the timer can't be set again in the meantime.
 */
static void kthread_cancel_delayed_work_timer(struct kthread_work *work,
					      unsigned long *flags)
{ … }

/*
 * This function removes the work from the worker queue.
 *
 * It is called under worker->lock. The caller must make sure that
 * the timer used by delayed work is not running, e.g. by calling
 * kthread_cancel_delayed_work_timer().
 *
 * The work might still be in use when this function finishes. See the
 * current_work proceed by the worker.
 *
 * Return: %true if @work was pending and successfully canceled,
 *	%false if @work was not pending
 */
static bool __kthread_cancel_work(struct kthread_work *work)
{ … }

/**
 * kthread_mod_delayed_work - modify delay of or queue a kthread delayed work
 * @worker: kthread worker to use
 * @dwork: kthread delayed work to queue
 * @delay: number of jiffies to wait before queuing
 *
 * If @dwork is idle, equivalent to kthread_queue_delayed_work(). Otherwise,
 * modify @dwork's timer so that it expires after @delay. If @delay is zero,
 * @work is guaranteed to be queued immediately.
 *
 * Return: %false if @dwork was idle and queued, %true otherwise.
 *
 * A special case is when the work is being canceled in parallel.
 * It might be caused either by the real kthread_cancel_delayed_work_sync()
 * or yet another kthread_mod_delayed_work() call. We let the other command
 * win and return %true here. The return value can be used for reference
 * counting and the number of queued works stays the same. Anyway, the caller
 * is supposed to synchronize these operations a reasonable way.
 *
 * This function is safe to call from any context including IRQ handler.
 * See __kthread_cancel_work() and kthread_delayed_work_timer_fn()
 * for details.
 */
bool kthread_mod_delayed_work(struct kthread_worker *worker,
			      struct kthread_delayed_work *dwork,
			      unsigned long delay)
{ … }
EXPORT_SYMBOL_GPL(…);

static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
{ … }

/**
 * kthread_cancel_work_sync - cancel a kthread work and wait for it to finish
 * @work: the kthread work to cancel
 *
 * Cancel @work and wait for its execution to finish.  This function
 * can be used even if the work re-queues itself. On return from this
 * function, @work is guaranteed to be not pending or executing on any CPU.
 *
 * kthread_cancel_work_sync(&delayed_work->work) must not be used for
 * delayed_work's. Use kthread_cancel_delayed_work_sync() instead.
 *
 * The caller must ensure that the worker on which @work was last
 * queued can't be destroyed before this function returns.
 *
 * Return: %true if @work was pending, %false otherwise.
 */
bool kthread_cancel_work_sync(struct kthread_work *work)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * kthread_cancel_delayed_work_sync - cancel a kthread delayed work and
 *	wait for it to finish.
 * @dwork: the kthread delayed work to cancel
 *
 * This is kthread_cancel_work_sync() for delayed works.
 *
 * Return: %true if @dwork was pending, %false otherwise.
 */
bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *dwork)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * kthread_flush_worker - flush all current works on a kthread_worker
 * @worker: worker to flush
 *
 * Wait until all currently executing or pending works on @worker are
 * finished.
 */
void kthread_flush_worker(struct kthread_worker *worker)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * kthread_destroy_worker - destroy a kthread worker
 * @worker: worker to be destroyed
 *
 * Flush and destroy @worker.  The simple flush is enough because the kthread
 * worker API is used only in trivial scenarios.  There are no multi-step state
 * machines needed.
 *
 * Note that this function is not responsible for handling delayed work, so
 * caller should be responsible for queuing or canceling all delayed work items
 * before invoke this function.
 */
void kthread_destroy_worker(struct kthread_worker *worker)
{ … }
EXPORT_SYMBOL(…);

/**
 * kthread_use_mm - make the calling kthread operate on an address space
 * @mm: address space to operate on
 */
void kthread_use_mm(struct mm_struct *mm)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * kthread_unuse_mm - reverse the effect of kthread_use_mm()
 * @mm: address space to operate on
 */
void kthread_unuse_mm(struct mm_struct *mm)
{ … }
EXPORT_SYMBOL_GPL(…);

#ifdef CONFIG_BLK_CGROUP
/**
 * kthread_associate_blkcg - associate blkcg to current kthread
 * @css: the cgroup info
 *
 * Current thread must be a kthread. The thread is running jobs on behalf of
 * other threads. In some cases, we expect the jobs attach cgroup info of
 * original threads instead of that of current thread. This function stores
 * original thread's cgroup info in current kthread context for later
 * retrieval.
 */
void kthread_associate_blkcg(struct cgroup_subsys_state *css)
{ … }
EXPORT_SYMBOL(…);

/**
 * kthread_blkcg - get associated blkcg css of current kthread
 *
 * Current thread must be a kthread.
 */
struct cgroup_subsys_state *kthread_blkcg(void)
{ … }
#endif