LXR linux-old/kernel/context.c

   1/*
   2 * linux/kernel/context.c
   3 *
   4 * Mechanism for running arbitrary tasks in process context
   5 *
   6 * dwmw2@redhat.com:            Genesis
   7 *
   8 * andrewm@uow.edu.au:          2.4.0-test12
   9 *      - Child reaping
  10 *      - Support for tasks which re-add themselves
  11 *      - flush_scheduled_tasks.
  12 */
  13
  14#define __KERNEL_SYSCALLS__
  15
  16#include <linux/module.h>
  17#include <linux/kernel.h>
  18#include <linux/sched.h>
  19#include <linux/init.h>
  20#include <linux/unistd.h>
  21#include <linux/signal.h>
  22#include <linux/completion.h>
  23
  24static DECLARE_TASK_QUEUE(tq_context);
  25static DECLARE_WAIT_QUEUE_HEAD(context_task_wq);
  26static DECLARE_WAIT_QUEUE_HEAD(context_task_done);
  27static int keventd_running;
  28static struct task_struct *keventd_task;
  29
  30static int need_keventd(const char *who)
  31{
  32        if (keventd_running == 0)
  33                printk(KERN_ERR "%s(): keventd has not started\n", who);
  34        return keventd_running;
  35}
  36        
  37int current_is_keventd(void)
  38{
  39        int ret = 0;
  40        if (need_keventd(__FUNCTION__))
  41                ret = (current == keventd_task);
  42        return ret;
  43}
  44
  45/**
  46 * schedule_task - schedule a function for subsequent execution in process context.
  47 * @task: pointer to a &tq_struct which defines the function to be scheduled.
  48 *
  49 * May be called from interrupt context.  The scheduled function is run at some
  50 * time in the near future by the keventd kernel thread.  If it can sleep, it
  51 * should be designed to do so for the minimum possible time, as it will be
  52 * stalling all other scheduled tasks.
  53 *
  54 * schedule_task() returns non-zero if the task was successfully scheduled.
  55 * If @task is already residing on a task queue then schedule_task() fails
  56 * to schedule your task and returns zero.
  57 */
  58int schedule_task(struct tq_struct *task)
  59{
  60        int ret;
  61        need_keventd(__FUNCTION__);
  62        ret = queue_task(task, &tq_context);
  63        wake_up(&context_task_wq);
  64        return ret;
  65}
  66
  67static int context_thread(void *startup)
  68{
  69        struct task_struct *curtask = current;
  70        DECLARE_WAITQUEUE(wait, curtask);
  71        struct k_sigaction sa;
  72
  73        daemonize();
  74        strcpy(curtask->comm, "keventd");
  75        keventd_running = 1;
  76        keventd_task = curtask;
  77
  78        spin_lock_irq(&curtask->sigmask_lock);
  79        siginitsetinv(&curtask->blocked, sigmask(SIGCHLD));
  80        recalc_sigpending(curtask);
  81        spin_unlock_irq(&curtask->sigmask_lock);
  82
  83        complete((struct completion *)startup);
  84
  85        /* Install a handler so SIGCLD is delivered */
  86        sa.sa.sa_handler = SIG_IGN;
  87        sa.sa.sa_flags = 0;
  88        siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
  89        do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
  90
  91        /*
  92         * If one of the functions on a task queue re-adds itself
  93         * to the task queue we call schedule() in state TASK_RUNNING
  94         */
  95        for (;;) {
  96                set_task_state(curtask, TASK_INTERRUPTIBLE);
  97                add_wait_queue(&context_task_wq, &wait);
  98                if (TQ_ACTIVE(tq_context))
  99                        set_task_state(curtask, TASK_RUNNING);
 100                schedule();
 101                remove_wait_queue(&context_task_wq, &wait);
 102                run_task_queue(&tq_context);
 103                wake_up(&context_task_done);
 104                if (signal_pending(curtask)) {
 105                        while (waitpid(-1, (unsigned int *)0, __WALL|WNOHANG) > 0)
 106                                ;
 107                        spin_lock_irq(&curtask->sigmask_lock);
 108                        flush_signals(curtask);
 109                        recalc_sigpending(curtask);
 110                        spin_unlock_irq(&curtask->sigmask_lock);
 111                }
 112        }
 113}
 114
 115/**
 116 * flush_scheduled_tasks - ensure that any scheduled tasks have run to completion.
 117 *
 118 * Forces execution of the schedule_task() queue and blocks until its completion.
 119 *
 120 * If a kernel subsystem uses schedule_task() and wishes to flush any pending
 121 * tasks, it should use this function.  This is typically used in driver shutdown
 122 * handlers.
 123 *
 124 * The caller should hold no spinlocks and should hold no semaphores which could
 125 * cause the scheduled tasks to block.
 126 */
 127static struct tq_struct dummy_task;
 128
 129void flush_scheduled_tasks(void)
 130{
 131        int count;
 132        DECLARE_WAITQUEUE(wait, current);
 133
 134        /*
 135         * Do it twice. It's possible, albeit highly unlikely, that
 136         * the caller queued a task immediately before calling us,
 137         * and that the eventd thread was already past the run_task_queue()
 138         * but not yet into wake_up(), so it woke us up before completing
 139         * the caller's queued task or our new dummy task.
 140         */
 141        add_wait_queue(&context_task_done, &wait);
 142        for (count = 0; count < 2; count++) {
 143                set_current_state(TASK_UNINTERRUPTIBLE);
 144
 145                /* Queue a dummy task to make sure we get kicked */
 146                schedule_task(&dummy_task);
 147
 148                /* Wait for it to complete */
 149                schedule();
 150        }
 151        remove_wait_queue(&context_task_done, &wait);
 152}
 153        
 154int start_context_thread(void)
 155{
 156        static struct completion startup __initdata = COMPLETION_INITIALIZER(startup);
 157
 158        kernel_thread(context_thread, &startup, CLONE_FS | CLONE_FILES);
 159        wait_for_completion(&startup);
 160        return 0;
 161}
 162
 163EXPORT_SYMBOL(schedule_task);
 164EXPORT_SYMBOL(flush_scheduled_tasks);
 165
 166