/* Kernel thread helper functions. * Copyright (C) 2004 IBM Corporation, Rusty Russell. * * Creation is done via keventd, so that we get a clean environment * even if we're invoked from userspace (think modprobe, hotplug cpu, * etc.). */ #include <linux/sched.h> #include <linux/kthread.h> #include <linux/completion.h> #include <linux/err.h> #include <linux/unistd.h> #include <linux/file.h> #include <linux/module.h> #include <linux/mutex.h> #include <asm/semaphore.h> /* * We dont want to execute off keventd since it might * hold a semaphore our callers hold too: */ static struct workqueue_struct *helper_wq; struct kthread_create_info { /* Information passed to kthread() from keventd. */ int (*threadfn)(void *data); void *data; struct completion started; /* Result passed back to kthread_create() from keventd. */ struct task_struct *result; struct completion done; struct work_struct work; }; struct kthread_stop_info { struct task_struct *k; int err; struct completion done; }; /* Thread stopping is done by setthing this var: lock serializes * multiple kthread_stop calls. */ static DEFINE_MUTEX(kthread_stop_lock); static struct kthread_stop_info kthread_stop_info; /** * 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(). */ int kthread_should_stop(void) { return (kthread_stop_info.k == current); } EXPORT_SYMBOL(kthread_should_stop); static void kthread_exit_files(void) { struct fs_struct *fs; struct task_struct *tsk = current; exit_fs(tsk); /* current->fs->count--; */ fs = init_task.fs; tsk->fs = fs; atomic_inc(&fs->count); exit_files(tsk); current->files = init_task.files; atomic_inc(&tsk->files->count); } static int kthread(void *_create) { struct kthread_create_info *create = _create; int (*threadfn)(void *data); void *data; sigset_t blocked; int ret = -EINTR; kthread_exit_files(); /* Copy data: it's on keventd's stack */ threadfn = create->threadfn; data = create->data; /* Block and flush all signals (in case we're not from keventd). */ sigfillset(&blocked); sigprocmask(SIG_BLOCK, &blocked, NULL); flush_signals(current); /* By default we can run anywhere, unlike keventd. */ set_cpus_allowed(current, CPU_MASK_ALL); /* OK, tell user we're spawned, wait for stop or wakeup */ __set_current_state(TASK_INTERRUPTIBLE); complete(&create->started); schedule(); if (!kthread_should_stop()) ret = threadfn(data); /* It might have exited on its own, w/o kthread_stop. Check. */ if (kthread_should_stop()) { kthread_stop_info.err = ret; complete(&kthread_stop_info.done); } return 0; } /* We are keventd: create a thread. */ static void keventd_create_kthread(struct work_struct *work) { struct kthread_create_info *create = container_of(work, struct kthread_create_info, work); int pid; /* 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) { create->result = ERR_PTR(pid); } else { wait_for_completion(&create->started); read_lock(&tasklist_lock); create->result = find_task_by_pid(pid); read_unlock(&tasklist_lock); } complete(&create->done); } /** * kthread_create - create a kthread. * @threadfn: the function to run until signal_pending(current). * @data: data ptr for @threadfn. * @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(), kthread_create_on_cpu(). * * When woken, the thread will run @threadfn() with @data as its * argument. @threadfn() can either call do_exit() directly if it is a * standalone thread for which noone 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). */ struct task_struct *kthread_create(int (*threadfn)(void *data), void *data, const char namefmt[], ...) { struct kthread_create_info create; create.threadfn = threadfn; create.data = data; init_completion(&create.started); init_completion(&create.done); INIT_WORK(&create.work, keventd_create_kthread); /* * The workqueue needs to start up first: */ if (!helper_wq) create.work.func(&create.work); else { queue_work(helper_wq, &create.work); wait_for_completion(&create.done); } if (!IS_ERR(create.result)) { va_list args; va_start(args, namefmt); vsnprintf(create.result->comm, sizeof(create.result->comm), namefmt, args); va_end(args); } return create.result; } EXPORT_SYMBOL(kthread_create); /** * kthread_bind - bind a just-created kthread to a cpu. * @k: 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 *k, unsigned int cpu) { BUG_ON(k->state != TASK_INTERRUPTIBLE); /* Must have done schedule() in kthread() before we set_task_cpu */ wait_task_inactive(k); set_task_cpu(k, cpu); k->cpus_allowed = cpumask_of_cpu(cpu); } EXPORT_SYMBOL(kthread_bind); /** * 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. Your threadfn() must not call do_exit() * itself if you use this function! This can also be called after * kthread_create() instead of calling wake_up_process(): the thread * will exit without calling threadfn(). * * Returns the result of threadfn(), or %-EINTR if wake_up_process() * was never called. */ int kthread_stop(struct task_struct *k) { int ret; mutex_lock(&kthread_stop_lock); /* It could exit after stop_info.k set, but before wake_up_process. */ get_task_struct(k); /* Must init completion *before* thread sees kthread_stop_info.k */ init_completion(&kthread_stop_info.done); smp_wmb(); /* Now set kthread_should_stop() to true, and wake it up. */ kthread_stop_info.k = k; wake_up_process(k); put_task_struct(k); /* Once it dies, reset stop ptr, gather result and we're done. */ wait_for_completion(&kthread_stop_info.done); kthread_stop_info.k = NULL; ret = kthread_stop_info.err; mutex_unlock(&kthread_stop_lock); return ret; } EXPORT_SYMBOL(kthread_stop); static __init int helper_init(void) { helper_wq = create_singlethread_workqueue("kthread"); BUG_ON(!helper_wq); return 0; } core_initcall(helper_init);