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
  24 static DECLARE_TASK_QUEUE(tq_context);
  25 static DECLARE_WAIT_QUEUE_HEAD(context_task_wq);
  26 static DECLARE_WAIT_QUEUE_HEAD(context_task_done);
  27 static int keventd_running;
  28 static struct task_struct *keventd_task;
  29
  30 static 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
  37 int 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  */
  58 int 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
  67 static 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  */
 127 static struct tq_struct dummy_task;
 128
 129 void 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
 154 int 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
 163 EXPORT_SYMBOL(schedule_task);
 164 EXPORT_SYMBOL(flush_scheduled_tasks);
 165