FreeBSD/Linux Kernel Cross Reference
sys/kernel/sched.c

     /*
      *  linux/kernel/sched.c
      *
      *  Kernel scheduler and related syscalls
      *
      *  Copyright (C) 1991, 1992  Linus Torvalds
      *
      *  1996-12-23  Modified by Dave Grothe to fix bugs in semaphores and
      *              make semaphores SMP safe
     *  1998-11-19  Implemented schedule_timeout() and related stuff
     *              by Andrea Arcangeli
     *  1998-12-28  Implemented better SMP scheduling by Ingo Molnar
     */
    
    /*
     * 'sched.c' is the main kernel file. It contains scheduling primitives
     * (sleep_on, wakeup, schedule etc) as well as a number of simple system
     * call functions (type getpid()), which just extract a field from
     * current-task
     */
    
    #include <linux/config.h>
    #include <linux/mm.h>
    #include <linux/init.h>
    #include <linux/smp_lock.h>
    #include <linux/nmi.h>
    #include <linux/interrupt.h>
    #include <linux/kernel_stat.h>
    #include <linux/completion.h>
    #include <linux/prefetch.h>
    #include <linux/compiler.h>
    
    #include <asm/uaccess.h>
    #include <asm/mmu_context.h>
    
    extern void timer_bh(void);
    extern void tqueue_bh(void);
    extern void immediate_bh(void);
    
    /*
     * scheduler variables
     */
    
    unsigned securebits = SECUREBITS_DEFAULT; /* systemwide security settings */
    
    extern void mem_use(void);
    
    /*
     * Scheduling quanta.
     *
     * NOTE! The unix "nice" value influences how long a process
     * gets. The nice value ranges from -20 to +19, where a -20
     * is a "high-priority" task, and a "+10" is a low-priority
     * task.
     *
     * We want the time-slice to be around 50ms or so, so this
     * calculation depends on the value of HZ.
     */
    #if HZ < 200
    #define TICK_SCALE(x)   ((x) >> 2)
    #elif HZ < 400
    #define TICK_SCALE(x)   ((x) >> 1)
    #elif HZ < 800
    #define TICK_SCALE(x)   (x)
    #elif HZ < 1600
    #define TICK_SCALE(x)   ((x) << 1)
    #else
    #define TICK_SCALE(x)   ((x) << 2)
    #endif
    
    #define NICE_TO_TICKS(nice)     (TICK_SCALE(20-(nice))+1)
    
    
    /*
     *      Init task must be ok at boot for the ix86 as we will check its signals
     *      via the SMP irq return path.
     */
     
    struct task_struct * init_tasks[NR_CPUS] = {&init_task, };
    
    /*
     * The tasklist_lock protects the linked list of processes.
     *
     * The runqueue_lock locks the parts that actually access
     * and change the run-queues, and have to be interrupt-safe.
     *
     * If both locks are to be concurrently held, the runqueue_lock
     * nests inside the tasklist_lock.
     *
     * task->alloc_lock nests inside tasklist_lock.
     */
    spinlock_t runqueue_lock __cacheline_aligned = SPIN_LOCK_UNLOCKED;  /* inner */
    rwlock_t tasklist_lock __cacheline_aligned = RW_LOCK_UNLOCKED;  /* outer */
    
    static LIST_HEAD(runqueue_head);
    
    /*
     * We align per-CPU scheduling data on cacheline boundaries,
     * to prevent cacheline ping-pong.
    */
   static union {
           struct schedule_data {
                   struct task_struct * curr;
                   cycles_t last_schedule;
           } schedule_data;
           char __pad [SMP_CACHE_BYTES];
   } aligned_data [NR_CPUS] __cacheline_aligned = { {{&init_task,0}}};
   
   #define cpu_curr(cpu) aligned_data[(cpu)].schedule_data.curr
   #define last_schedule(cpu) aligned_data[(cpu)].schedule_data.last_schedule
   
   struct kernel_stat kstat;
   extern struct task_struct *child_reaper;
   
   #ifdef CONFIG_SMP
   
   #define idle_task(cpu) (init_tasks[cpu_number_map(cpu)])
   #define can_schedule(p,cpu) \
           ((p)->cpus_runnable & (p)->cpus_allowed & (1UL << cpu))
   
   #else
   
   #define idle_task(cpu) (&init_task)
   #define can_schedule(p,cpu) (1)
   
   #endif
   
   void scheduling_functions_start_here(void) { }
   
   /*
    * This is the function that decides how desirable a process is..
    * You can weigh different processes against each other depending
    * on what CPU they've run on lately etc to try to handle cache
    * and TLB miss penalties.
    *
    * Return values:
    *       -1000: never select this
    *           0: out of time, recalculate counters (but it might still be
    *              selected)
    *         +ve: "goodness" value (the larger, the better)
    *       +1000: realtime process, select this.
    */
   
   static inline int goodness(struct task_struct * p, int this_cpu, struct mm_struct *this_mm)
   {
           int weight;
   
           /*
            * select the current process after every other
            * runnable process, but before the idle thread.
            * Also, dont trigger a counter recalculation.
            */
           weight = -1;
           if (p->policy & SCHED_YIELD)
                   goto out;
   
           /*
            * Non-RT process - normal case first.
            */
           if (p->policy == SCHED_OTHER) {
                   /*
                    * Give the process a first-approximation goodness value
                    * according to the number of clock-ticks it has left.
                    *
                    * Don't do any other calculations if the time slice is
                    * over..
                    */
                   weight = p->counter;
                   if (!weight)
                           goto out;
                           
   #ifdef CONFIG_SMP
                   /* Give a largish advantage to the same processor...   */
                   /* (this is equivalent to penalizing other processors) */
                   if (p->processor == this_cpu)
                           weight += PROC_CHANGE_PENALTY;
   #endif
   
                   /* .. and a slight advantage to the current MM */
                   if (p->mm == this_mm || !p->mm)
                           weight += 1;
                   weight += 20 - p->nice;
                   goto out;
           }
   
           /*
            * Realtime process, select the first one on the
            * runqueue (taking priorities within processes
            * into account).
            */
           weight = 1000 + p->rt_priority;
   out:
           return weight;
   }
   
   /*
    * the 'goodness value' of replacing a process on a given CPU.
    * positive value means 'replace', zero or negative means 'dont'.
    */
   static inline int preemption_goodness(struct task_struct * prev, struct task_struct * p, int cpu)
   {
           return goodness(p, cpu, prev->active_mm) - goodness(prev, cpu, prev->active_mm);
   }
   
   /*
    * This is ugly, but reschedule_idle() is very timing-critical.
    * We are called with the runqueue spinlock held and we must
    * not claim the tasklist_lock.
    */
   static FASTCALL(void reschedule_idle(struct task_struct * p));
   
   static void reschedule_idle(struct task_struct * p)
   {
   #ifdef CONFIG_SMP
           int this_cpu = smp_processor_id();
           struct task_struct *tsk, *target_tsk;
           int cpu, best_cpu, i, max_prio;
           cycles_t oldest_idle;
   
           /*
            * shortcut if the woken up task's last CPU is
            * idle now.
            */
           best_cpu = p->processor;
           if (can_schedule(p, best_cpu)) {
                   tsk = idle_task(best_cpu);
                   if (cpu_curr(best_cpu) == tsk) {
                           int need_resched;
   send_now_idle:
                           /*
                            * If need_resched == -1 then we can skip sending
                            * the IPI altogether, tsk->need_resched is
                            * actively watched by the idle thread.
                            */
                           need_resched = tsk->need_resched;
                           tsk->need_resched = 1;
                           if ((best_cpu != this_cpu) && !need_resched)
                                   smp_send_reschedule(best_cpu);
                           return;
                   }
           }
   
           /*
            * We know that the preferred CPU has a cache-affine current
            * process, lets try to find a new idle CPU for the woken-up
            * process. Select the least recently active idle CPU. (that
            * one will have the least active cache context.) Also find
            * the executing process which has the least priority.
            */
           oldest_idle = (cycles_t) -1;
           target_tsk = NULL;
           max_prio = 0;
   
           for (i = 0; i < smp_num_cpus; i++) {
                   cpu = cpu_logical_map(i);
                   if (!can_schedule(p, cpu))
                           continue;
                   tsk = cpu_curr(cpu);
                   /*
                    * We use the first available idle CPU. This creates
                    * a priority list between idle CPUs, but this is not
                    * a problem.
                    */
                   if (tsk == idle_task(cpu)) {
   #if defined(__i386__) && defined(CONFIG_SMP)
                           /*
                            * Check if two siblings are idle in the same
                            * physical package. Use them if found.
                            */
                           if (smp_num_siblings == 2) {
                                   if (cpu_curr(cpu_sibling_map[cpu]) == 
                                       idle_task(cpu_sibling_map[cpu])) {
                                           oldest_idle = last_schedule(cpu);
                                           target_tsk = tsk;
                                           break;
                                   }
                                   
                           }
   #endif          
                           if (last_schedule(cpu) < oldest_idle) {
                                   oldest_idle = last_schedule(cpu);
                                   target_tsk = tsk;
                           }
                   } else {
                           if (oldest_idle == (cycles_t)-1) {
                                   int prio = preemption_goodness(tsk, p, cpu);
   
                                   if (prio > max_prio) {
                                           max_prio = prio;
                                           target_tsk = tsk;
                                   }
                           }
                   }
           }
           tsk = target_tsk;
           if (tsk) {
                   if (oldest_idle != (cycles_t)-1) {
                           best_cpu = tsk->processor;
                           goto send_now_idle;
                   }
                   tsk->need_resched = 1;
                   if (tsk->processor != this_cpu)
                           smp_send_reschedule(tsk->processor);
           }
           return;
                   
   
   #else /* UP */
           int this_cpu = smp_processor_id();
           struct task_struct *tsk;
   
           tsk = cpu_curr(this_cpu);
           if (preemption_goodness(tsk, p, this_cpu) > 0)
                   tsk->need_resched = 1;
   #endif
   }
   
   /*
    * Careful!
    *
    * This has to add the process to the _end_ of the 
    * run-queue, not the beginning. The goodness value will
    * determine whether this process will run next. This is
    * important to get SCHED_FIFO and SCHED_RR right, where
    * a process that is either pre-empted or its time slice
    * has expired, should be moved to the tail of the run 
    * queue for its priority - Bhavesh Davda
    */
   static inline void add_to_runqueue(struct task_struct * p)
   {
           list_add_tail(&p->run_list, &runqueue_head);
           nr_running++;
   }
   
   static inline void move_last_runqueue(struct task_struct * p)
   {
           list_del(&p->run_list);
           list_add_tail(&p->run_list, &runqueue_head);
   }
   
   /*
    * Wake up a process. Put it on the run-queue if it's not
    * already there.  The "current" process is always on the
    * run-queue (except when the actual re-schedule is in
    * progress), and as such you're allowed to do the simpler
    * "current->state = TASK_RUNNING" to mark yourself runnable
    * without the overhead of this.
    */
   static inline int try_to_wake_up(struct task_struct * p, int synchronous)
   {
           unsigned long flags;
           int success = 0;
   
           /*
            * We want the common case fall through straight, thus the goto.
            */
           spin_lock_irqsave(&runqueue_lock, flags);
           p->state = TASK_RUNNING;
           if (task_on_runqueue(p))
                   goto out;
           add_to_runqueue(p);
           if (!synchronous || !(p->cpus_allowed & (1UL << smp_processor_id())))
                   reschedule_idle(p);
           success = 1;
   out:
           spin_unlock_irqrestore(&runqueue_lock, flags);
           return success;
   }
   
   inline int wake_up_process(struct task_struct * p)
   {
           return try_to_wake_up(p, 0);
   }
   
   static void process_timeout(unsigned long __data)
   {
           struct task_struct * p = (struct task_struct *) __data;
   
           wake_up_process(p);
   }
   
   /**
    * schedule_timeout - sleep until timeout
    * @timeout: timeout value in jiffies
    *
    * Make the current task sleep until @timeout jiffies have
    * elapsed. The routine will return immediately unless
    * the current task state has been set (see set_current_state()).
    *
    * You can set the task state as follows -
    *
    * %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
    * pass before the routine returns. The routine will return 0
    *
    * %TASK_INTERRUPTIBLE - the routine may return early if a signal is
    * delivered to the current task. In this case the remaining time
    * in jiffies will be returned, or 0 if the timer expired in time
    *
    * The current task state is guaranteed to be TASK_RUNNING when this 
    * routine returns.
    *
    * Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
    * the CPU away without a bound on the timeout. In this case the return
    * value will be %MAX_SCHEDULE_TIMEOUT.
    *
    * In all cases the return value is guaranteed to be non-negative.
    */
   signed long schedule_timeout(signed long timeout)
   {
           struct timer_list timer;
           unsigned long expire;
   
           switch (timeout)
           {
           case MAX_SCHEDULE_TIMEOUT:
                   /*
                    * These two special cases are useful to be comfortable
                    * in the caller. Nothing more. We could take
                    * MAX_SCHEDULE_TIMEOUT from one of the negative value
                    * but I' d like to return a valid offset (>=0) to allow
                    * the caller to do everything it want with the retval.
                    */
                   schedule();
                   goto out;
           default:
                   /*
                    * Another bit of PARANOID. Note that the retval will be
                    * 0 since no piece of kernel is supposed to do a check
                    * for a negative retval of schedule_timeout() (since it
                    * should never happens anyway). You just have the printk()
                    * that will tell you if something is gone wrong and where.
                    */
                   if (timeout < 0)
                   {
                           printk(KERN_ERR "schedule_timeout: wrong timeout "
                                  "value %lx from %p\n", timeout,
                                  __builtin_return_address(0));
                           current->state = TASK_RUNNING;
                           goto out;
                   }
           }
   
           expire = timeout + jiffies;
   
           init_timer(&timer);
           timer.expires = expire;
           timer.data = (unsigned long) current;
           timer.function = process_timeout;
   
           add_timer(&timer);
           schedule();
           del_timer_sync(&timer);
   
           timeout = expire - jiffies;
   
    out:
           return timeout < 0 ? 0 : timeout;
   }
   
   /*
    * schedule_tail() is getting called from the fork return path. This
    * cleans up all remaining scheduler things, without impacting the
    * common case.
    */
   static inline void __schedule_tail(struct task_struct *prev)
   {
   #ifdef CONFIG_SMP
           int policy;
   
           /*
            * prev->policy can be written from here only before `prev'
            * can be scheduled (before setting prev->cpus_runnable to ~0UL).
            * Of course it must also be read before allowing prev
            * to be rescheduled, but since the write depends on the read
            * to complete, wmb() is enough. (the spin_lock() acquired
            * before setting cpus_runnable is not enough because the spin_lock()
            * common code semantics allows code outside the critical section
            * to enter inside the critical section)
            */
           policy = prev->policy;
           prev->policy = policy & ~SCHED_YIELD;
           wmb();
   
           /*
            * fast path falls through. We have to clear cpus_runnable before
            * checking prev->state to avoid a wakeup race. Protect against
            * the task exiting early.
            */
           task_lock(prev);
           task_release_cpu(prev);
           mb();
           if (prev->state == TASK_RUNNING)
                   goto needs_resched;
   
   out_unlock:
           task_unlock(prev);      /* Synchronise here with release_task() if prev is TASK_ZOMBIE */
           return;
   
           /*
            * Slow path - we 'push' the previous process and
            * reschedule_idle() will attempt to find a new
            * processor for it. (but it might preempt the
            * current process as well.) We must take the runqueue
            * lock and re-check prev->state to be correct. It might
            * still happen that this process has a preemption
            * 'in progress' already - but this is not a problem and
            * might happen in other circumstances as well.
            */
   needs_resched:
           {
                   unsigned long flags;
   
                   /*
                    * Avoid taking the runqueue lock in cases where
                    * no preemption-check is necessery:
                    */
                   if ((prev == idle_task(smp_processor_id())) ||
                                                   (policy & SCHED_YIELD))
                           goto out_unlock;
   
                   spin_lock_irqsave(&runqueue_lock, flags);
                   if ((prev->state == TASK_RUNNING) && !task_has_cpu(prev))
                           reschedule_idle(prev);
                   spin_unlock_irqrestore(&runqueue_lock, flags);
                   goto out_unlock;
           }
   #else
           prev->policy &= ~SCHED_YIELD;
   #endif /* CONFIG_SMP */
   }
   
   asmlinkage void schedule_tail(struct task_struct *prev)
   {
           __schedule_tail(prev);
   }
   
   /*
    *  'schedule()' is the scheduler function. It's a very simple and nice
    * scheduler: it's not perfect, but certainly works for most things.
    *
    * The goto is "interesting".
    *
    *   NOTE!!  Task 0 is the 'idle' task, which gets called when no other
    * tasks can run. It can not be killed, and it cannot sleep. The 'state'
    * information in task[0] is never used.
    */
   asmlinkage void schedule(void)
   {
           struct schedule_data * sched_data;
           struct task_struct *prev, *next, *p;
           struct list_head *tmp;
           int this_cpu, c;
   
   
           spin_lock_prefetch(&runqueue_lock);
   
           BUG_ON(!current->active_mm);
   need_resched_back:
           prev = current;
           this_cpu = prev->processor;
   
           if (unlikely(in_interrupt())) {
                   printk("Scheduling in interrupt\n");
                   BUG();
           }
   
           release_kernel_lock(prev, this_cpu);
   
           /*
            * 'sched_data' is protected by the fact that we can run
            * only one process per CPU.
            */
           sched_data = & aligned_data[this_cpu].schedule_data;
   
           spin_lock_irq(&runqueue_lock);
   
           /* move an exhausted RR process to be last.. */
           if (unlikely(prev->policy == SCHED_RR))
                   if (!prev->counter) {
                           prev->counter = NICE_TO_TICKS(prev->nice);
                           move_last_runqueue(prev);
                   }
   
           switch (prev->state) {
                   case TASK_INTERRUPTIBLE:
                           if (signal_pending(prev)) {
                                   prev->state = TASK_RUNNING;
                                   break;
                           }
                   default:
                           del_from_runqueue(prev);
                   case TASK_RUNNING:;
           }
           prev->need_resched = 0;
   
           /*
            * this is the scheduler proper:
            */
   
   repeat_schedule:
           /*
            * Default process to select..
            */
           next = idle_task(this_cpu);
           c = -1000;
           list_for_each(tmp, &runqueue_head) {
                   p = list_entry(tmp, struct task_struct, run_list);
                   if (can_schedule(p, this_cpu)) {
                           int weight = goodness(p, this_cpu, prev->active_mm);
                           if (weight > c)
                                   c = weight, next = p;
                   }
           }
   
           /* Do we need to re-calculate counters? */
           if (unlikely(!c)) {
                   struct task_struct *p;
   
                   spin_unlock_irq(&runqueue_lock);
                   read_lock(&tasklist_lock);
                   for_each_task(p)
                           p->counter = (p->counter >> 1) + NICE_TO_TICKS(p->nice);
                   read_unlock(&tasklist_lock);
                   spin_lock_irq(&runqueue_lock);
                   goto repeat_schedule;
           }
   
           /*
            * from this point on nothing can prevent us from
            * switching to the next task, save this fact in
            * sched_data.
            */
           sched_data->curr = next;
           task_set_cpu(next, this_cpu);
           spin_unlock_irq(&runqueue_lock);
   
           if (unlikely(prev == next)) {
                   /* We won't go through the normal tail, so do this by hand */
                   prev->policy &= ~SCHED_YIELD;
                   goto same_process;
           }
   
   #ifdef CONFIG_SMP
           /*
            * maintain the per-process 'last schedule' value.
            * (this has to be recalculated even if we reschedule to
            * the same process) Currently this is only used on SMP,
            * and it's approximate, so we do not have to maintain
            * it while holding the runqueue spinlock.
            */
           sched_data->last_schedule = get_cycles();
   
           /*
            * We drop the scheduler lock early (it's a global spinlock),
            * thus we have to lock the previous process from getting
            * rescheduled during switch_to().
            */
   
   #endif /* CONFIG_SMP */
   
           kstat.context_swtch++;
           /*
            * there are 3 processes which are affected by a context switch:
            *
            * prev == .... ==> (last => next)
            *
            * It's the 'much more previous' 'prev' that is on next's stack,
            * but prev is set to (the just run) 'last' process by switch_to().
            * This might sound slightly confusing but makes tons of sense.
            */
           prepare_to_switch();
           {
                   struct mm_struct *mm = next->mm;
                   struct mm_struct *oldmm = prev->active_mm;
                   if (!mm) {
                           BUG_ON(next->active_mm);
                           next->active_mm = oldmm;
                           atomic_inc(&oldmm->mm_count);
                           enter_lazy_tlb(oldmm, next, this_cpu);
                   } else {
                           BUG_ON(next->active_mm != mm);
                           switch_mm(oldmm, mm, next, this_cpu);
                   }
   
                   if (!prev->mm) {
                           prev->active_mm = NULL;
                           mmdrop(oldmm);
                   }
           }
   
           /*
            * This just switches the register state and the
            * stack.
            */
           switch_to(prev, next, prev);
           __schedule_tail(prev);
   
   same_process:
           reacquire_kernel_lock(current);
           if (current->need_resched)
                   goto need_resched_back;
           return;
   }
   
   /*
    * The core wakeup function.  Non-exclusive wakeups (nr_exclusive == 0) just wake everything
    * up.  If it's an exclusive wakeup (nr_exclusive == small +ve number) then we wake all the
    * non-exclusive tasks and one exclusive task.
    *
    * There are circumstances in which we can try to wake a task which has already
    * started to run but is not in state TASK_RUNNING.  try_to_wake_up() returns zero
    * in this (rare) case, and we handle it by contonuing to scan the queue.
    */
   static inline void __wake_up_common (wait_queue_head_t *q, unsigned int mode,
                                        int nr_exclusive, const int sync)
   {
           struct list_head *tmp;
           struct task_struct *p;
   
           CHECK_MAGIC_WQHEAD(q);
           WQ_CHECK_LIST_HEAD(&q->task_list);
           
           list_for_each(tmp,&q->task_list) {
                   unsigned int state;
                   wait_queue_t *curr = list_entry(tmp, wait_queue_t, task_list);
   
                   CHECK_MAGIC(curr->__magic);
                   p = curr->task;
                   state = p->state;
                   if (state & mode) {
                           WQ_NOTE_WAKER(curr);
                           if (try_to_wake_up(p, sync) && (curr->flags&WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
                                   break;
                   }
           }
   }
   
   void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr)
   {
           if (q) {
                   unsigned long flags;
                   wq_read_lock_irqsave(&q->lock, flags);
                   __wake_up_common(q, mode, nr, 0);
                   wq_read_unlock_irqrestore(&q->lock, flags);
           }
   }
   
   void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr)
   {
           if (q) {
                   unsigned long flags;
                   wq_read_lock_irqsave(&q->lock, flags);
                   __wake_up_common(q, mode, nr, 1);
                   wq_read_unlock_irqrestore(&q->lock, flags);
           }
   }
   
   void complete(struct completion *x)
   {
           unsigned long flags;
   
           spin_lock_irqsave(&x->wait.lock, flags);
           x->done++;
           __wake_up_common(&x->wait, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1, 0);
           spin_unlock_irqrestore(&x->wait.lock, flags);
   }
   
   void wait_for_completion(struct completion *x)
   {
           spin_lock_irq(&x->wait.lock);
           if (!x->done) {
                   DECLARE_WAITQUEUE(wait, current);
   
                   wait.flags |= WQ_FLAG_EXCLUSIVE;
                   __add_wait_queue_tail(&x->wait, &wait);
                   do {
                           __set_current_state(TASK_UNINTERRUPTIBLE);
                           spin_unlock_irq(&x->wait.lock);
                           schedule();
                           spin_lock_irq(&x->wait.lock);
                   } while (!x->done);
                   __remove_wait_queue(&x->wait, &wait);
           }
           x->done--;
           spin_unlock_irq(&x->wait.lock);
   }
   
   #define SLEEP_ON_VAR                            \
           unsigned long flags;                    \
           wait_queue_t wait;                      \
           init_waitqueue_entry(&wait, current);
   
   #define SLEEP_ON_HEAD                                   \
           wq_write_lock_irqsave(&q->lock,flags);          \
           __add_wait_queue(q, &wait);                     \
           wq_write_unlock(&q->lock);
   
   #define SLEEP_ON_TAIL                                           \
           wq_write_lock_irq(&q->lock);                            \
           __remove_wait_queue(q, &wait);                          \
           wq_write_unlock_irqrestore(&q->lock,flags);
   
   void interruptible_sleep_on(wait_queue_head_t *q)
   {
           SLEEP_ON_VAR
   
           current->state = TASK_INTERRUPTIBLE;
   
           SLEEP_ON_HEAD
           schedule();
           SLEEP_ON_TAIL
   }
   
   long interruptible_sleep_on_timeout(wait_queue_head_t *q, long timeout)
   {
           SLEEP_ON_VAR
   
           current->state = TASK_INTERRUPTIBLE;
   
           SLEEP_ON_HEAD
           timeout = schedule_timeout(timeout);
           SLEEP_ON_TAIL
   
           return timeout;
   }
   
   void sleep_on(wait_queue_head_t *q)
   {
           SLEEP_ON_VAR
           
           current->state = TASK_UNINTERRUPTIBLE;
   
           SLEEP_ON_HEAD
           schedule();
           SLEEP_ON_TAIL
   }
   
   long sleep_on_timeout(wait_queue_head_t *q, long timeout)
   {
           SLEEP_ON_VAR
           
           current->state = TASK_UNINTERRUPTIBLE;
   
           SLEEP_ON_HEAD
           timeout = schedule_timeout(timeout);
           SLEEP_ON_TAIL
   
           return timeout;
   }
   
   void scheduling_functions_end_here(void) { }
   
   #if CONFIG_SMP
   /**
    * set_cpus_allowed() - change a given task's processor affinity
    * @p: task to bind
    * @new_mask: bitmask of allowed processors
    *
    * Upon return, the task is running on a legal processor.  Note the caller
    * must have a valid reference to the task: it must not exit() prematurely.
    * This call can sleep; do not hold locks on call.
    */
   void set_cpus_allowed(struct task_struct *p, unsigned long new_mask)
   {
           new_mask &= cpu_online_map;
           BUG_ON(!new_mask);
   
           p->cpus_allowed = new_mask;
   
           /*
            * If the task is on a no-longer-allowed processor, we need to move
            * it.  If the task is not current, then set need_resched and send
            * its processor an IPI to reschedule.
            */
           if (!(p->cpus_runnable & p->cpus_allowed)) {
                   if (p != current) {
                           p->need_resched = 1;
                           smp_send_reschedule(p->processor);
                   }
                   /*
                    * Wait until we are on a legal processor.  If the task is
                    * current, then we should be on a legal processor the next
                    * time we reschedule.  Otherwise, we need to wait for the IPI.
                    */
                   while (!(p->cpus_runnable & p->cpus_allowed))
                           schedule();
           }
   }
   #endif /* CONFIG_SMP */
   
   #ifndef __alpha__
   
   /*
    * This has been replaced by sys_setpriority.  Maybe it should be
    * moved into the arch dependent tree for those ports that require
    * it for backward compatibility?
    */
   
   asmlinkage long sys_nice(int increment)
   {
           long newprio;
   
           /*
            *      Setpriority might change our priority at the same moment.
            *      We don't have to worry. Conceptually one call occurs first
            *      and we have a single winner.
            */
           if (increment < 0) {
                   if (!capable(CAP_SYS_NICE))
                           return -EPERM;
                   if (increment < -40)
                           increment = -40;
           }
           if (increment > 40)
                   increment = 40;
   
           newprio = current->nice + increment;
           if (newprio < -20)
                   newprio = -20;
           if (newprio > 19)
                   newprio = 19;
           current->nice = newprio;
           return 0;
   }
   
   #endif
   
   static inline struct task_struct *find_process_by_pid(pid_t pid)
   {
           struct task_struct *tsk = current;
   
           if (pid)
                   tsk = find_task_by_pid(pid);
           return tsk;
   }
   
   static int setscheduler(pid_t pid, int policy, 
                           struct sched_param *param)
   {
           struct sched_param lp;
           struct task_struct *p;
           int retval;
   
           retval = -EINVAL;
           if (!param || pid < 0)
                   goto out_nounlock;
   
           retval = -EFAULT;
           if (copy_from_user(&lp, param, sizeof(struct sched_param)))
                   goto out_nounlock;
   
           /*
            * We play safe to avoid deadlocks.
            */
           read_lock_irq(&tasklist_lock);
           spin_lock(&runqueue_lock);
   
           p = find_process_by_pid(pid);
   
           retval = -ESRCH;
           if (!p)
                   goto out_unlock;
                           
           if (policy < 0)
                   policy = p->policy;
           else {
                   retval = -EINVAL;
                   if (policy != SCHED_FIFO && policy != SCHED_RR &&
                                   policy != SCHED_OTHER)
                           goto out_unlock;
           }
           
           /*
            * Valid priorities for SCHED_FIFO and SCHED_RR are 1..99, valid
            * priority for SCHED_OTHER is 0.
            */
           retval = -EINVAL;
           if (lp.sched_priority < 0 || lp.sched_priority > 99)
                   goto out_unlock;
           if ((policy == SCHED_OTHER) != (lp.sched_priority == 0))
                   goto out_unlock;
   
           retval = -EPERM;
           if ((policy == SCHED_FIFO || policy == SCHED_RR) && 
               !capable(CAP_SYS_NICE))
                   goto out_unlock;
           if ((current->euid != p->euid) && (current->euid != p->uid) &&
               !capable(CAP_SYS_NICE))
                   goto out_unlock;
   
           retval = 0;
           p->policy = policy;
           p->rt_priority = lp.sched_priority;
   
           current->need_resched = 1;
   
   out_unlock:
           spin_unlock(&runqueue_lock);
           read_unlock_irq(&tasklist_lock);
  
  out_nounlock:
          return retval;
  }
  
  asmlinkage long sys_sched_setscheduler(pid_t pid, int policy, 
                                        struct sched_param *param)
  {
          return setscheduler(pid, policy, param);
  }
  
  asmlinkage long sys_sched_setparam(pid_t pid, struct sched_param *param)
  {
          return setscheduler(pid, -1, param);
  }
  
  asmlinkage long sys_sched_getscheduler(pid_t pid)
  {
          struct task_struct *p;
          int retval;
  
          retval = -EINVAL;
          if (pid < 0)
                  goto out_nounlock;
  
          retval = -ESRCH;
          read_lock(&tasklist_lock);
          p = find_process_by_pid(pid);
          if (p)
                  retval = p->policy & ~SCHED_YIELD;
          read_unlock(&tasklist_lock);
  
  out_nounlock:
          return retval;
  }
  
  asmlinkage long sys_sched_getparam(pid_t pid, struct sched_param *param)
  {
          struct task_struct *p;
          struct sched_param lp;
          int retval;
  
          retval = -EINVAL;
          if (!param || pid < 0)
                  goto out_nounlock;
  
          read_lock(&tasklist_lock);
          p = find_process_by_pid(pid);
          retval = -ESRCH;
          if (!p)
                  goto out_unlock;
          lp.sched_priority = p->rt_priority;
          read_unlock(&tasklist_lock);
  
          /*
           * This one might sleep, we cannot do it with a spinlock held ...
           */
          retval = copy_to_user(param, &lp, sizeof(*param)) ? -EFAULT : 0;
  
  out_nounlock:
          return retval;
  
  out_unlock:
          read_unlock(&tasklist_lock);
          return retval;
  }
  
  asmlinkage long sys_sched_yield(void)
  {
          /*
           * Trick. sched_yield() first counts the number of truly 
           * 'pending' runnable processes, then returns if it's
           * only the current processes. (This test does not have
           * to be atomic.) In threaded applications this optimization
           * gets triggered quite often.
           */
  
          int nr_pending = nr_running;
  
  #if CONFIG_SMP
          int i;
  
          // Subtract non-idle processes running on other CPUs.
          for (i = 0; i < smp_num_cpus; i++) {
                  int cpu = cpu_logical_map(i);
                  if (aligned_data[cpu].schedule_data.curr != idle_task(cpu))
                          nr_pending--;
          }
  #else
          // on UP this process is on the runqueue as well
          nr_pending--;
  #endif
          if (nr_pending) {
                  /*
                   * This process can only be rescheduled by us,
                   * so this is safe without any locking.
                   */
                  if (current->policy == SCHED_OTHER)
                          current->policy |= SCHED_YIELD;
                  current->need_resched = 1;
  
                  spin_lock_irq(&runqueue_lock);
                  move_last_runqueue(current);
                  spin_unlock_irq(&runqueue_lock);
          }
          return 0;
  }
  
  /**
   * yield - yield the current processor to other threads.
   *
   * this is a shortcut for kernel-space yielding - it marks the
   * thread runnable and calls sys_sched_yield().
   */
  void yield(void)
  {
          set_current_state(TASK_RUNNING);
          sys_sched_yield();
          schedule();
  }
  
  void __cond_resched(void)
  {
          set_current_state(TASK_RUNNING);
          schedule();
  }
  
  asmlinkage long sys_sched_get_priority_max(int policy)
  {
          int ret = -EINVAL;
  
          switch (policy) {
          case SCHED_FIFO:
          case SCHED_RR:
                  ret = 99;
                  break;
          case SCHED_OTHER:
                  ret = 0;
                  break;
          }
          return ret;
  }
  
  asmlinkage long sys_sched_get_priority_min(int policy)
  {
          int ret = -EINVAL;
  
          switch (policy) {
          case SCHED_FIFO:
          case SCHED_RR:
                  ret = 1;
                  break;
          case SCHED_OTHER:
                  ret = 0;
          }
          return ret;
  }
  
  asmlinkage long sys_sched_rr_get_interval(pid_t pid, struct timespec *interval)
  {
          struct timespec t;
          struct task_struct *p;
          int retval = -EINVAL;
  
          if (pid < 0)
                  goto out_nounlock;
  
          retval = -ESRCH;
          read_lock(&tasklist_lock);
          p = find_process_by_pid(pid);
          if (p)
                  jiffies_to_timespec(p->policy & SCHED_FIFO ? 0 : NICE_TO_TICKS(p->nice),
                                      &t);
          read_unlock(&tasklist_lock);
          if (p)
                  retval = copy_to_user(interval, &t, sizeof(t)) ? -EFAULT : 0;
  out_nounlock:
          return retval;
  }
  
  static void show_task(struct task_struct * p)
  {
          unsigned long free = 0;
          int state;
          static const char * stat_nam[] = { "R", "S", "D", "Z", "T", "W" };
  
          printk("%-13.13s ", p->comm);
          state = p->state ? ffz(~p->state) + 1 : 0;
          if (((unsigned) state) < sizeof(stat_nam)/sizeof(char *))
                  printk(stat_nam[state]);
          else
                  printk(" ");
  #if (BITS_PER_LONG == 32)
          if (p == current)
                  printk(" current  ");
          else
                  printk(" %08lX ", thread_saved_pc(&p->thread));
  #else
          if (p == current)
                  printk("   current task   ");
          else
                  printk(" %016lx ", thread_saved_pc(&p->thread));
  #endif
          {
                  unsigned long * n = (unsigned long *) (p+1);
                  while (!*n)
                          n++;
                  free = (unsigned long) n - (unsigned long)(p+1);
          }
          printk("%5lu %5d %6d ", free, p->pid, p->p_pptr->pid);
          if (p->p_cptr)
                  printk("%5d ", p->p_cptr->pid);
          else
                  printk("      ");
          if (p->p_ysptr)
                  printk("%7d", p->p_ysptr->pid);
          else
                  printk("       ");
          if (p->p_osptr)
                  printk(" %5d", p->p_osptr->pid);
          else
                  printk("      ");
          if (!p->mm)
                  printk(" (L-TLB)\n");
          else
                  printk(" (NOTLB)\n");
  
          {
                  extern void show_trace_task(struct task_struct *tsk);
                  show_trace_task(p);
          }
  }
  
  char * render_sigset_t(sigset_t *set, char *buffer)
  {
          int i = _NSIG, x;
          do {
                  i -= 4, x = 0;
                  if (sigismember(set, i+1)) x |= 1;
                  if (sigismember(set, i+2)) x |= 2;
                  if (sigismember(set, i+3)) x |= 4;
                  if (sigismember(set, i+4)) x |= 8;
                  *buffer++ = (x < 10 ? '' : 'a' - 10) + x;
          } while (i >= 4);
          *buffer = 0;
          return buffer;
  }
  
  void show_state(void)
  {
          struct task_struct *p;
  
  #if (BITS_PER_LONG == 32)
          printk("\n"
                 "                         free                        sibling\n");
          printk("  task             PC    stack   pid father child younger older\n");
  #else
          printk("\n"
                 "                                 free                        sibling\n");
          printk("  task                 PC        stack   pid father child younger older\n");
  #endif
          read_lock(&tasklist_lock);
          for_each_task(p) {
                  /*
                   * reset the NMI-timeout, listing all files on a slow
                   * console might take alot of time:
                   */
                  touch_nmi_watchdog();
                  show_task(p);
          }
          read_unlock(&tasklist_lock);
  }
  
  /**
   * reparent_to_init() - Reparent the calling kernel thread to the init task.
   *
   * If a kernel thread is launched as a result of a system call, or if
   * it ever exits, it should generally reparent itself to init so that
   * it is correctly cleaned up on exit.
   *
   * The various task state such as scheduling policy and priority may have
   * been inherited fro a user process, so we reset them to sane values here.
   *
   * NOTE that reparent_to_init() gives the caller full capabilities.
   */
  void reparent_to_init(void)
  {
          struct task_struct *this_task = current;
  
          write_lock_irq(&tasklist_lock);
  
          /* Reparent to init */
          REMOVE_LINKS(this_task);
          this_task->p_pptr = child_reaper;
          this_task->p_opptr = child_reaper;
          SET_LINKS(this_task);
  
          /* Set the exit signal to SIGCHLD so we signal init on exit */
          this_task->exit_signal = SIGCHLD;
  
          /* We also take the runqueue_lock while altering task fields
           * which affect scheduling decisions */
          spin_lock(&runqueue_lock);
  
          this_task->ptrace = 0;
          this_task->nice = DEF_NICE;
          this_task->policy = SCHED_OTHER;
          /* cpus_allowed? */
          /* rt_priority? */
          /* signals? */
          this_task->cap_effective = CAP_INIT_EFF_SET;
          this_task->cap_inheritable = CAP_INIT_INH_SET;
          this_task->cap_permitted = CAP_FULL_SET;
          this_task->keep_capabilities = 0;
          memcpy(this_task->rlim, init_task.rlim, sizeof(*(this_task->rlim)));
          this_task->user = INIT_USER;
  
          spin_unlock(&runqueue_lock);
          write_unlock_irq(&tasklist_lock);
  }
  
  /*
   *      Put all the gunge required to become a kernel thread without
   *      attached user resources in one place where it belongs.
   */
  
  void daemonize(void)
  {
          struct fs_struct *fs;
  
  
          /*
           * If we were started as result of loading a module, close all of the
           * user space pages.  We don't need them, and if we didn't close them
           * they would be locked into memory.
           */
          exit_mm(current);
  
          current->session = 1;
          current->pgrp = 1;
          current->tty = NULL;
  
          /* Become as one with the init task */
  
          exit_fs(current);       /* current->fs->count--; */
          fs = init_task.fs;
          current->fs = fs;
          atomic_inc(&fs->count);
          exit_files(current);
          current->files = init_task.files;
          atomic_inc(&current->files->count);
  }
  
  extern unsigned long wait_init_idle;
  
  void __init init_idle(void)
  {
          struct schedule_data * sched_data;
          sched_data = &aligned_data[smp_processor_id()].schedule_data;
  
          if (current != &init_task && task_on_runqueue(current)) {
                  printk("UGH! (%d:%d) was on the runqueue, removing.\n",
                          smp_processor_id(), current->pid);
                  del_from_runqueue(current);
          }
          sched_data->curr = current;
          sched_data->last_schedule = get_cycles();
          clear_bit(current->processor, &wait_init_idle);
  }
  
  extern void init_timervecs (void);
  
  void __init sched_init(void)
  {
          /*
           * We have to do a little magic to get the first
           * process right in SMP mode.
           */
          int cpu = smp_processor_id();
          int nr;
  
          init_task.processor = cpu;
  
          for(nr = 0; nr < PIDHASH_SZ; nr++)
                  pidhash[nr] = NULL;
  
          init_timervecs();
  
          init_bh(TIMER_BH, timer_bh);
          init_bh(TQUEUE_BH, tqueue_bh);
          init_bh(IMMEDIATE_BH, immediate_bh);
  
          /*
           * The boot idle thread does lazy MMU switching as well:
           */
          atomic_inc(&init_mm.mm_count);
          enter_lazy_tlb(&init_mm, current, cpu);
  }

Cache object: 7951f31cde4a34166456ae2825a9fc3e