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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // 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. */
     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);
 
 bool __kthread_should_park(struct task_struct *k)
 {
     return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(k)->flags);
 }
 EXPORT_SYMBOL_GPL(__kthread_should_park);
 
 /**
  * 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);
 
 /**
  * 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 task state
          * changin from TASK_PARKED and us failing the
          * wait_task_inactive() in kthread_park().
          */
         set_special_state(TASK_PARKED);
         if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
             break;
 
         /*
          * Thread is going to call schedule(), do not preempt it,
          * or the caller of kthread_park() may spend more time in
          * wait_task_inactive().
          */
         preempt_disable();
         complete(&self->parked);
         schedule_preempt_disabled();
         preempt_enable();
     }
     __set_current_state(TASK_RUNNING);
 }
 
 void kthread_parkme(void)
 {
     __kthread_parkme(to_kthread(current));
 }
 EXPORT_SYMBOL_GPL(kthread_parkme);
 
 /**
  * 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)
 {
     struct kthread *kthread = to_kthread(current);
     kthread->result = result;
     do_exit(0);
 }
 
 /**
  * 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 the reuturn code to kthread_stop().
  *
  * A kernel thread whose module may be removed after the completion of
  * @comp can use this function exit safely.
  *
  * Does not return.
  */
 void __noreturn kthread_complete_and_exit(struct completion *comp, long code)
 {
     if (comp)
         complete(comp);
 
     kthread_exit(code);
 }
 EXPORT_SYMBOL(kthread_complete_and_exit);
 
 static int kthread(void *_create)
 {
     static const struct sched_param param = { .sched_priority = 0 };
     /* Copy data: it's on kthread's stack */
     struct kthread_create_info *create = _create;
     int (*threadfn)(void *data) = create->threadfn;
     void *data = create->data;
     struct completion *done;
     struct kthread *self;
     int ret;
 
     self = to_kthread(current);
 
     /* Release the structure when caller killed by a fatal signal. */
     done = xchg(&create->done, NULL);
     if (!done) {
         kfree(create);
         kthread_exit(-EINTR);
     }
 
     self->threadfn = threadfn;
     self->data = data;
 
     /*
      * The new thread inherited kthreadd's priority and CPU mask. Reset
      * back to default in case they have been changed.
      */
     sched_setscheduler_nocheck(current, SCHED_NORMAL, &param);
     set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_KTHREAD));
 
     /* OK, tell user we're spawned, wait for stop or wakeup */
     __set_current_state(TASK_UNINTERRUPTIBLE);
     create->result = current;
     /*
      * Thread is going to call schedule(), do not preempt it,
      * or the creator may spend more time in wait_task_inactive().
      */
     preempt_disable();
     complete(done);
     schedule_preempt_disabled();
     preempt_enable();
 
     ret = -EINTR;
     if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
         cgroup_kthread_ready();
         __kthread_parkme(self);
         ret = threadfn(data);
     }
     kthread_exit(ret);
 }
 
 /* called from kernel_clone() to get node information for about to be created task */
 int tsk_fork_get_node(struct task_struct *tsk)
 {
 #ifdef CONFIG_NUMA
     if (tsk == kthreadd_task)
         return tsk->pref_node_fork;
 #endif
     return NUMA_NO_NODE;
 }
 
 static void create_kthread(struct kthread_create_info *create)
 {
     int pid;
 
 #ifdef CONFIG_NUMA
     current->pref_node_fork = create->node;
 #endif
     /* We want our own signal handler (we take no signals by default). */
     pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
     if (pid < 0) {
         /* Release the structure when caller killed by a fatal signal. */
         struct completion *done = xchg(&create->done, NULL);
 
         if (!done) {
             kfree(create);
             return;
         }
         create->result = ERR_PTR(pid);
         complete(done);
     }
 }
 
 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)
 {
     DECLARE_COMPLETION_ONSTACK(done);
     struct task_struct *task;
     struct kthread_create_info *create = kmalloc(sizeof(*create),
                              GFP_KERNEL);
 
     if (!create)
         return ERR_PTR(-ENOMEM);
     create->threadfn = threadfn;
     create->data = data;
     create->node = node;
     create->done = &done;
 
     spin_lock(&kthread_create_lock);
     list_add_tail(&create->list, &kthread_create_list);
     spin_unlock(&kthread_create_lock);
 
     wake_up_process(kthreadd_task);
     /*
      * Wait for completion in killable state, for I might be chosen by
      * the OOM killer while kthreadd is trying to allocate memory for
      * new kernel thread.
      */
     if (unlikely(wait_for_completion_killable(&done))) {
         /*
          * If I was killed by a fatal signal before kthreadd (or new
          * kernel thread) calls complete(), leave the cleanup of this
          * structure to that thread.
          */
         if (xchg(&create->done, NULL))
             return ERR_PTR(-EINTR);
         /*
          * kthreadd (or new kernel thread) will call complete()
          * shortly.
          */
         wait_for_completion(&done);
     }
     task = create->result;
     if (!IS_ERR(task)) {
         char name[TASK_COMM_LEN];
         va_list aq;
         int len;
 
         /*
          * task is already visible to other tasks, so updating
          * COMM must be protected.
          */
         va_copy(aq, args);
         len = vsnprintf(name, sizeof(name), namefmt, aq);
         va_end(aq);
         if (len >= TASK_COMM_LEN) {
             struct kthread *kthread = to_kthread(task);
 
             /* leave it truncated when out of memory. */
             kthread->full_name = kvasprintf(GFP_KERNEL, namefmt, args);
         }
         set_task_comm(task, name);
     }
     kfree(create);
     return task;
 }
 
 /**
  * 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[],
                        ...)
 {
     struct task_struct *task;
     va_list args;
 
     va_start(args, namefmt);
     task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
     va_end(args);
 
     return task;
 }
 EXPORT_SYMBOL(kthread_create_on_node);
 
 static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, unsigned int state)
 {
     unsigned long flags;
 
     if (!wait_task_inactive(p, state)) {
         WARN_ON(1);
         return;
     }
 
     /* It's safe because the task is inactive. */
     raw_spin_lock_irqsave(&p->pi_lock, flags);
     do_set_cpus_allowed(p, mask);
     p->flags |= PF_NO_SETAFFINITY;
     raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 }
 
 static void __kthread_bind(struct task_struct *p, unsigned int cpu, unsigned int state)
 {
     __kthread_bind_mask(p, cpumask_of(cpu), state);
 }
 
 void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
 {
     __kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
 }
 
 /**
  * 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)
 {
     __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
 }
 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
  */
 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;
     kthread_bind(p, cpu);
     /* CPU hotplug need to bind once again when unparking the thread. */
     to_kthread(p)->cpu = cpu;
     return p;
 }
 EXPORT_SYMBOL(kthread_create_on_cpu);
 
 void kthread_set_per_cpu(struct task_struct *k, int cpu)
 {
     struct kthread *kthread = to_kthread(k);
     if (!kthread)
         return;
 
     WARN_ON_ONCE(!(k->flags & PF_NO_SETAFFINITY));
 
     if (cpu < 0) {
         clear_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
         return;
     }
 
     kthread->cpu = cpu;
     set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
 }
 
 bool kthread_is_per_cpu(struct task_struct *p)
 {
     struct kthread *kthread = __to_kthread(p);
     if (!kthread)
         return false;
 
     return test_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
 }
 
 /**
  * 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 = to_kthread(k);
 
     /*
      * Newly created kthread was parked when the CPU was offline.
      * The binding was lost and we need to set it again.
      */
     if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
         __kthread_bind(k, kthread->cpu, TASK_PARKED);
 
     clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
     /*
      * __kthread_parkme() will either see !SHOULD_PARK or get the wakeup.
      */
     wake_up_state(k, TASK_PARKED);
 }
 EXPORT_SYMBOL_GPL(kthread_unpark);
 
 /**
  * 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 = to_kthread(k);
 
     if (WARN_ON(k->flags & PF_EXITING))
         return -ENOSYS;
 
     if (WARN_ON_ONCE(test_bit(KTHREAD_SHOULD_PARK, &kthread->flags)))
         return -EBUSY;
 
     set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
     if (k != current) {
         wake_up_process(k);
         /*
          * Wait for __kthread_parkme() to complete(), this means we
          * _will_ have TASK_PARKED and are about to call schedule().
          */
         wait_for_completion(&kthread->parked);
         /*
          * Now wait for that schedule() to complete and the task to
          * get scheduled out.
          */
         WARN_ON_ONCE(!wait_task_inactive(k, TASK_PARKED));
     }
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(kthread_park);
 
 /**
  * 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)
 {
     struct kthread *kthread;
     int ret;
 
     trace_sched_kthread_stop(k);
 
     get_task_struct(k);
     kthread = to_kthread(k);
     set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
     kthread_unpark(k);
     wake_up_process(k);
     wait_for_completion(&kthread->exited);
     ret = kthread->result;
     put_task_struct(k);
 
     trace_sched_kthread_stop_ret(ret);
     return ret;
 }
 EXPORT_SYMBOL(kthread_stop);
 
 int kthreadd(void *unused)
 {
     struct task_struct *tsk = current;
 
     /* Setup a clean context for our children to inherit. */
     set_task_comm(tsk, "kthreadd");
     ignore_signals(tsk);
     set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_TYPE_KTHREAD));
     set_mems_allowed(node_states[N_MEMORY]);
 
     current->flags |= PF_NOFREEZE;
     cgroup_init_kthreadd();
 
     for (;;) {
         set_current_state(TASK_INTERRUPTIBLE);
         if (list_empty(&kthread_create_list))
             schedule();
         __set_current_state(TASK_RUNNING);
 
         spin_lock(&kthread_create_lock);
         while (!list_empty(&kthread_create_list)) {
             struct kthread_create_info *create;
 
             create = list_entry(kthread_create_list.next,
                         struct kthread_create_info, list);
             list_del_init(&create->list);
             spin_unlock(&kthread_create_lock);
 
             create_kthread(create);
 
             spin_lock(&kthread_create_lock);
         }
         spin_unlock(&kthread_create_lock);
     }
 
     return 0;
 }
 
 void __kthread_init_worker(struct kthread_worker *worker,
                 const char *name,
                 struct lock_class_key *key)
 {
     memset(worker, 0, sizeof(struct kthread_worker));
     raw_spin_lock_init(&worker->lock);
     lockdep_set_class_and_name(&worker->lock, key, name);
     INIT_LIST_HEAD(&worker->work_list);
     INIT_LIST_HEAD(&worker->delayed_work_list);
 }
 EXPORT_SYMBOL_GPL(__kthread_init_worker);
 
 /**
  * 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)
 {
     struct kthread_worker *worker = worker_ptr;
     struct kthread_work *work;
 
     /*
      * FIXME: Update the check and remove the assignment when all kthread
      * worker users are created using kthread_create_worker*() functions.
      */
     WARN_ON(worker->task && worker->task != current);
     worker->task = current;
 
     if (worker->flags & KTW_FREEZABLE)
         set_freezable();
 
 repeat:
     set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 
     if (kthread_should_stop()) {
         __set_current_state(TASK_RUNNING);
         raw_spin_lock_irq(&worker->lock);
         worker->task = NULL;
         raw_spin_unlock_irq(&worker->lock);
         return 0;
     }
 
     work = NULL;
     raw_spin_lock_irq(&worker->lock);
     if (!list_empty(&worker->work_list)) {
         work = list_first_entry(&worker->work_list,
                     struct kthread_work, node);
         list_del_init(&work->node);
     }
     worker->current_work = work;
     raw_spin_unlock_irq(&worker->lock);
 
     if (work) {
         kthread_work_func_t func = work->func;
         __set_current_state(TASK_RUNNING);
         trace_sched_kthread_work_execute_start(work);
         work->func(work);
         /*
          * Avoid dereferencing work after this point.  The trace
          * event only cares about the address.
          */
         trace_sched_kthread_work_execute_end(work, func);
     } else if (!freezing(current))
         schedule();
 
     try_to_freeze();
     cond_resched();
     goto repeat;
 }
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
 static __printf(3, 0) struct kthread_worker *
 __kthread_create_worker(int cpu, unsigned int flags,
             const char namefmt[], va_list args)
 {
     struct kthread_worker *worker;
     struct task_struct *task;
     int node = NUMA_NO_NODE;
 
     worker = kzalloc(sizeof(*worker), GFP_KERNEL);
     if (!worker)
         return ERR_PTR(-ENOMEM);
 
     kthread_init_worker(worker);
 
     if (cpu >= 0)
         node = cpu_to_node(cpu);
 
     task = __kthread_create_on_node(kthread_worker_fn, worker,
                         node, namefmt, args);
     if (IS_ERR(task))
         goto fail_task;
 
     if (cpu >= 0)
         kthread_bind(task, cpu);
 
     worker->flags = flags;
     worker->task = task;
     wake_up_process(task);
     return worker;
 
 fail_task:
     kfree(worker);
     return ERR_CAST(task);
 }
 
 /**
  * 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[], ...)
 {
     struct kthread_worker *worker;
     va_list args;
 
     va_start(args, namefmt);
     worker = __kthread_create_worker(-1, flags, namefmt, args);
     va_end(args);
 
     return worker;
 }
 EXPORT_SYMBOL(kthread_create_worker);
 
 /**
  * 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[], ...)
 {
     struct kthread_worker *worker;
     va_list args;
 
     va_start(args, namefmt);
     worker = __kthread_create_worker(cpu, flags, namefmt, args);
     va_end(args);
 
     return worker;
 }
 EXPORT_SYMBOL(kthread_create_worker_on_cpu);
 
 /*
  * 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)
 {
     lockdep_assert_held(&worker->lock);
 
     return !list_empty(&work->node) || work->canceling;
 }
 
 static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
                          struct kthread_work *work)
 {
     lockdep_assert_held(&worker->lock);
     WARN_ON_ONCE(!list_empty(&work->node));
     /* Do not use a work with >1 worker, see kthread_queue_work() */
     WARN_ON_ONCE(work->worker && work->worker != worker);
 }
 
 /* insert @work before @pos in @worker */
 static void kthread_insert_work(struct kthread_worker *worker,
                 struct kthread_work *work,
                 struct list_head *pos)
 {
     kthread_insert_work_sanity_check(worker, work);
 
     trace_sched_kthread_work_queue_work(worker, work);
 
     list_add_tail(&work->node, pos);
     work->worker = worker;
     if (!worker->current_work && likely(worker->task))
         wake_up_process(worker->task);
 }
 
 /**
  * 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)
 {
     bool ret = false;
     unsigned long flags;
 
     raw_spin_lock_irqsave(&worker->lock, flags);
     if (!queuing_blocked(worker, work)) {
         kthread_insert_work(worker, work, &worker->work_list);
         ret = true;
     }
     raw_spin_unlock_irqrestore(&worker->lock, flags);
     return ret;
 }
 EXPORT_SYMBOL_GPL(kthread_queue_work);
 
 /**
  * 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)
 {
     struct kthread_delayed_work *dwork = from_timer(dwork, t, timer);
     struct kthread_work *work = &dwork->work;
     struct kthread_worker *worker = work->worker;
     unsigned long flags;
 
     /*
      * This might happen when a pending work is reinitialized.
      * It means that it is used a wrong way.
      */
     if (WARN_ON_ONCE(!worker))
         return;
 
     raw_spin_lock_irqsave(&worker->lock, flags);
     /* Work must not be used with >1 worker, see kthread_queue_work(). */
     WARN_ON_ONCE(work->worker != worker);
 
     /* Move the work from worker->delayed_work_list. */
     WARN_ON_ONCE(list_empty(&work->node));
     list_del_init(&work->node);
     if (!work->canceling)
         kthread_insert_work(worker, work, &worker->work_list);
 
     raw_spin_unlock_irqrestore(&worker->lock, flags);
 }
 EXPORT_SYMBOL(kthread_delayed_work_timer_fn);
 
 static void __kthread_queue_delayed_work(struct kthread_worker *worker,
                      struct kthread_delayed_work *dwork,
                      unsigned long delay)
 {
     struct timer_list *timer = &dwork->timer;
     struct kthread_work *work = &dwork->work;
 
     WARN_ON_FUNCTION_MISMATCH(timer->function,
                   kthread_delayed_work_timer_fn);
 
     /*
      * If @delay is 0, queue @dwork->work immediately.  This is for
      * both optimization and correctness.  The earliest @timer can
      * expire is on the closest next tick and delayed_work users depend
      * on that there's no such delay when @delay is 0.
      */
     if (!delay) {
         kthread_insert_work(worker, work, &worker->work_list);
         return;
     }
 
     /* Be paranoid and try to detect possible races already now. */
     kthread_insert_work_sanity_check(worker, work);
 
     list_add(&work->node, &worker->delayed_work_list);
     work->worker = worker;
     timer->expires = jiffies + delay;
     add_timer(timer);
 }
 
 /**
  * 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)
 {
     struct kthread_work *work = &dwork->work;
     unsigned long flags;
     bool ret = false;
 
     raw_spin_lock_irqsave(&worker->lock, flags);
 
     if (!queuing_blocked(worker, work)) {
         __kthread_queue_delayed_work(worker, dwork, delay);
         ret = true;
     }
 
     raw_spin_unlock_irqrestore(&worker->lock, flags);
     return ret;
 }
 EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);
 
 struct kthread_flush_work {
     struct kthread_work work;
     struct completion   done;
 };
 
 static void kthread_flush_work_fn(struct kthread_work *work)
 {
     struct kthread_flush_work *fwork =
         container_of(work, struct kthread_flush_work, work);
     complete(&fwork->done);
 }
 
 /**
  * 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)
 {
     struct kthread_flush_work fwork = {
         KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
         COMPLETION_INITIALIZER_ONSTACK(fwork.done),
     };
     struct kthread_worker *worker;
     bool noop = false;
 
     worker = work->worker;
     if (!worker)
         return;
 
     raw_spin_lock_irq(&worker->lock);
     /* Work must not be used with >1 worker, see kthread_queue_work(). */
     WARN_ON_ONCE(work->worker != worker);
 
     if (!list_empty(&work->node))
         kthread_insert_work(worker, &fwork.work, work->node.next);
     else if (worker->current_work == work)
         kthread_insert_work(worker, &fwork.work,
                     worker->work_list.next);
     else
         noop = true;
 
     raw_spin_unlock_irq(&worker->lock);
 
     if (!noop)
         wait_for_completion(&fwork.done);
 }
 EXPORT_SYMBOL_GPL(kthread_flush_work);
 
 /*
  * 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)
 {
     struct kthread_delayed_work *dwork =
         container_of(work, struct kthread_delayed_work, work);
     struct kthread_worker *worker = work->worker;
 
     /*
      * del_timer_sync() must be called to make sure that the timer
      * callback is not running. The lock must be temporary released
      * to avoid a deadlock with the callback. In the meantime,
      * any queuing is blocked by setting the canceling counter.
      */
     work->canceling++;
     raw_spin_unlock_irqrestore(&worker->lock, *flags);
     del_timer_sync(&dwork->timer);
     raw_spin_lock_irqsave(&worker->lock, *flags);
     work->canceling--;
 }
 
 /*
  * 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)
 {
     /*
      * Try to remove the work from a worker list. It might either
      * be from worker->work_list or from worker->delayed_work_list.
      */
     if (!list_empty(&work->node)) {
         list_del_init(&work->node);
         return true;
     }
 
     return false;
 }
 
 /**
  * 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)
 {
     struct kthread_work *work = &dwork->work;
     unsigned long flags;
     int ret;
 
     raw_spin_lock_irqsave(&worker->lock, flags);
 
     /* Do not bother with canceling when never queued. */
     if (!work->worker) {
         ret = false;
         goto fast_queue;
     }
 
     /* Work must not be used with >1 worker, see kthread_queue_work() */
     WARN_ON_ONCE(work->worker != worker);
 
     /*
      * Temporary cancel the work but do not fight with another command
      * that is canceling the work as well.
      *
      * It is a bit tricky because of possible races with another
      * mod_delayed_work() and cancel_delayed_work() callers.
      *
      * The timer must be canceled first because worker->lock is released
      * when doing so. But the work can be removed from the queue (list)
      * only when it can be queued again so that the return value can
      * be used for reference counting.
      */
     kthread_cancel_delayed_work_timer(work, &flags);
     if (work->canceling) {
         /* The number of works in the queue does not change. */
         ret = true;
         goto out;
     }
     ret = __kthread_cancel_work(work);
 
 fast_queue:
     __kthread_queue_delayed_work(worker, dwork, delay);
 out:
     raw_spin_unlock_irqrestore(&worker->lock, flags);
     return ret;
 }
 EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);
 
 static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
 {
     struct kthread_worker *worker = work->worker;
     unsigned long flags;
     int ret = false;
 
     if (!worker)
         goto out;
 
     raw_spin_lock_irqsave(&worker->lock, flags);
     /* Work must not be used with >1 worker, see kthread_queue_work(). */
     WARN_ON_ONCE(work->worker != worker);
 
     if (is_dwork)
         kthread_cancel_delayed_work_timer(work, &flags);
 
     ret = __kthread_cancel_work(work);
 
     if (worker->current_work != work)
         goto out_fast;
 
     /*
      * The work is in progress and we need to wait with the lock released.
      * In the meantime, block any queuing by setting the canceling counter.
      */
     work->canceling++;
     raw_spin_unlock_irqrestore(&worker->lock, flags);
     kthread_flush_work(work);
     raw_spin_lock_irqsave(&worker->lock, flags);
     work->canceling--;
 
 out_fast:
     raw_spin_unlock_irqrestore(&worker->lock, flags);
 out:
     return ret;
 }
 
 /**
  * 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)
 {
     return __kthread_cancel_work_sync(work, false);
 }
 EXPORT_SYMBOL_GPL(kthread_cancel_work_sync);
 
 /**
  * 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)
 {
     return __kthread_cancel_work_sync(&dwork->work, true);
 }
 EXPORT_SYMBOL_GPL(kthread_cancel_delayed_work_sync);
 
 /**
  * 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)
 {
     struct kthread_flush_work fwork = {
         KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
         COMPLETION_INITIALIZER_ONSTACK(fwork.done),
     };
 
     kthread_queue_work(worker, &fwork.work);
     wait_for_completion(&fwork.done);
 }
 EXPORT_SYMBOL_GPL(kthread_flush_worker);
 
 /**
  * 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.
  */
 void kthread_destroy_worker(struct kthread_worker *worker)
 {
     struct task_struct *task;
 
     task = worker->task;
     if (WARN_ON(!task))
         return;
 
     kthread_flush_worker(worker);
     kthread_stop(task);
     WARN_ON(!list_empty(&worker->work_list));
     kfree(worker);
 }
 EXPORT_SYMBOL(kthread_destroy_worker);
 
 /**
  * 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)
 {
     struct mm_struct *active_mm;
     struct task_struct *tsk = current;
 
     WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
     WARN_ON_ONCE(tsk->mm);
 
     task_lock(tsk);
     /* Hold off tlb flush IPIs while switching mm's */
     local_irq_disable();
     active_mm = tsk->active_mm;
     if (active_mm != mm) {
         mmgrab(mm);
         tsk->active_mm = mm;
     }
     tsk->mm = mm;
     membarrier_update_current_mm(mm);
     switch_mm_irqs_off(active_mm, mm, tsk);
     local_irq_enable();
     task_unlock(tsk);
 #ifdef finish_arch_post_lock_switch
     finish_arch_post_lock_switch();
 #endif
 
     /*
      * When a kthread starts operating on an address space, the loop
      * in membarrier_{private,global}_expedited() may not observe
      * that tsk->mm, and not issue an IPI. Membarrier requires a
      * memory barrier after storing to tsk->mm, before accessing
      * user-space memory. A full memory barrier for membarrier
      * {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by
      * mmdrop(), or explicitly with smp_mb().
      */
     if (active_mm != mm)
         mmdrop(active_mm);
     else
         smp_mb();
 }
 EXPORT_SYMBOL_GPL(kthread_use_mm);
 
 /**
  * kthread_unuse_mm - reverse the effect of kthread_use_mm()
  * @mm: address space to operate on
  */
 void kthread_unuse_mm(struct mm_struct *mm)
 {
     struct task_struct *tsk = current;
 
     WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
     WARN_ON_ONCE(!tsk->mm);
 
     task_lock(tsk);
     /*
      * When a kthread stops operating on an address space, the loop
      * in membarrier_{private,global}_expedited() may not observe
      * that tsk->mm, and not issue an IPI. Membarrier requires a
      * memory barrier after accessing user-space memory, before
      * clearing tsk->mm.
      */
     smp_mb__after_spinlock();
     sync_mm_rss(mm);
     local_irq_disable();
     tsk->mm = NULL;
     membarrier_update_current_mm(NULL);
     /* active_mm is still 'mm' */
     enter_lazy_tlb(mm, tsk);
     local_irq_enable();
     task_unlock(tsk);
 }
 EXPORT_SYMBOL_GPL(kthread_unuse_mm);
 
 #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)
 {
     struct kthread *kthread;
 
     if (!(current->flags & PF_KTHREAD))
         return;
     kthread = to_kthread(current);
     if (!kthread)
         return;
 
     if (kthread->blkcg_css) {
         css_put(kthread->blkcg_css);
         kthread->blkcg_css = NULL;
     }
     if (css) {
         css_get(css);
         kthread->blkcg_css = css;
     }
 }
 EXPORT_SYMBOL(kthread_associate_blkcg);
 
 /**
  * kthread_blkcg - get associated blkcg css of current kthread
  *
  * Current thread must be a kthread.
  */
 struct cgroup_subsys_state *kthread_blkcg(void)
 {
     struct kthread *kthread;
 
     if (current->flags & PF_KTHREAD) {
         kthread = to_kthread(current);
         if (kthread)
             return kthread->blkcg_css;
     }
     return NULL;
 }
 #endif

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