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

     /*
      * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
      *
      * This program is free software; you can redistribute it and/or modify
      * it under the terms of the GNU General Public License as published by
      * the Free Software Foundation; either version 2 of the License, or
      * (at your option) any later version.
      *
      * This program is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU General Public License for more details.
     *
     * You should have received a copy of the GNU General Public License
     * along with this program; if not, write to the Free Software
     * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
     *
     * Copyright IBM Corporation, 2008
     *
     * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
     *
     * For detailed explanation of Read-Copy Update mechanism see -
     *              Documentation/RCU
     */
    #include <linux/completion.h>
    #include <linux/interrupt.h>
    #include <linux/notifier.h>
    #include <linux/rcupdate.h>
    #include <linux/kernel.h>
    #include <linux/export.h>
    #include <linux/mutex.h>
    #include <linux/sched.h>
    #include <linux/types.h>
    #include <linux/init.h>
    #include <linux/time.h>
    #include <linux/cpu.h>
    #include <linux/prefetch.h>
    
    #ifdef CONFIG_RCU_TRACE
    #include <trace/events/rcu.h>
    #endif /* #else #ifdef CONFIG_RCU_TRACE */
    
    #include "rcu.h"
    
    /* Forward declarations for rcutiny_plugin.h. */
    struct rcu_ctrlblk;
    static void invoke_rcu_callbacks(void);
    static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
    static void rcu_process_callbacks(struct softirq_action *unused);
    static void __call_rcu(struct rcu_head *head,
                           void (*func)(struct rcu_head *rcu),
                           struct rcu_ctrlblk *rcp);
    
    #include "rcutiny_plugin.h"
    
    static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
    
    /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
    static void rcu_idle_enter_common(long long newval)
    {
            if (newval) {
                    RCU_TRACE(trace_rcu_dyntick("--=",
                                                rcu_dynticks_nesting, newval));
                    rcu_dynticks_nesting = newval;
                    return;
            }
            RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
            if (!is_idle_task(current)) {
                    struct task_struct *idle = idle_task(smp_processor_id());
    
                    RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
                                                rcu_dynticks_nesting, newval));
                    ftrace_dump(DUMP_ALL);
                    WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
                              current->pid, current->comm,
                              idle->pid, idle->comm); /* must be idle task! */
            }
            rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
            barrier();
            rcu_dynticks_nesting = newval;
    }
    
    /*
     * Enter idle, which is an extended quiescent state if we have fully
     * entered that mode (i.e., if the new value of dynticks_nesting is zero).
     */
    void rcu_idle_enter(void)
    {
            unsigned long flags;
            long long newval;
    
            local_irq_save(flags);
            WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
            if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
                DYNTICK_TASK_NEST_VALUE)
                    newval = 0;
            else
                    newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
            rcu_idle_enter_common(newval);
           local_irq_restore(flags);
   }
   EXPORT_SYMBOL_GPL(rcu_idle_enter);
   
   /*
    * Exit an interrupt handler towards idle.
    */
   void rcu_irq_exit(void)
   {
           unsigned long flags;
           long long newval;
   
           local_irq_save(flags);
           newval = rcu_dynticks_nesting - 1;
           WARN_ON_ONCE(newval < 0);
           rcu_idle_enter_common(newval);
           local_irq_restore(flags);
   }
   EXPORT_SYMBOL_GPL(rcu_irq_exit);
   
   /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
   static void rcu_idle_exit_common(long long oldval)
   {
           if (oldval) {
                   RCU_TRACE(trace_rcu_dyntick("++=",
                                               oldval, rcu_dynticks_nesting));
                   return;
           }
           RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
           if (!is_idle_task(current)) {
                   struct task_struct *idle = idle_task(smp_processor_id());
   
                   RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
                             oldval, rcu_dynticks_nesting));
                   ftrace_dump(DUMP_ALL);
                   WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
                             current->pid, current->comm,
                             idle->pid, idle->comm); /* must be idle task! */
           }
   }
   
   /*
    * Exit idle, so that we are no longer in an extended quiescent state.
    */
   void rcu_idle_exit(void)
   {
           unsigned long flags;
           long long oldval;
   
           local_irq_save(flags);
           oldval = rcu_dynticks_nesting;
           WARN_ON_ONCE(rcu_dynticks_nesting < 0);
           if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
                   rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
           else
                   rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
           rcu_idle_exit_common(oldval);
           local_irq_restore(flags);
   }
   EXPORT_SYMBOL_GPL(rcu_idle_exit);
   
   /*
    * Enter an interrupt handler, moving away from idle.
    */
   void rcu_irq_enter(void)
   {
           unsigned long flags;
           long long oldval;
   
           local_irq_save(flags);
           oldval = rcu_dynticks_nesting;
           rcu_dynticks_nesting++;
           WARN_ON_ONCE(rcu_dynticks_nesting == 0);
           rcu_idle_exit_common(oldval);
           local_irq_restore(flags);
   }
   EXPORT_SYMBOL_GPL(rcu_irq_enter);
   
   #ifdef CONFIG_DEBUG_LOCK_ALLOC
   
   /*
    * Test whether RCU thinks that the current CPU is idle.
    */
   int rcu_is_cpu_idle(void)
   {
           return !rcu_dynticks_nesting;
   }
   EXPORT_SYMBOL(rcu_is_cpu_idle);
   
   #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
   
   /*
    * Test whether the current CPU was interrupted from idle.  Nested
    * interrupts don't count, we must be running at the first interrupt
    * level.
    */
   int rcu_is_cpu_rrupt_from_idle(void)
   {
           return rcu_dynticks_nesting <= 1;
   }
   
   /*
    * Helper function for rcu_sched_qs() and rcu_bh_qs().
    * Also irqs are disabled to avoid confusion due to interrupt handlers
    * invoking call_rcu().
    */
   static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
   {
           if (rcp->rcucblist != NULL &&
               rcp->donetail != rcp->curtail) {
                   rcp->donetail = rcp->curtail;
                   return 1;
           }
   
           return 0;
   }
   
   /*
    * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
    * are at it, given that any rcu quiescent state is also an rcu_bh
    * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
    */
   void rcu_sched_qs(int cpu)
   {
           unsigned long flags;
   
           local_irq_save(flags);
           if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
               rcu_qsctr_help(&rcu_bh_ctrlblk))
                   invoke_rcu_callbacks();
           local_irq_restore(flags);
   }
   
   /*
    * Record an rcu_bh quiescent state.
    */
   void rcu_bh_qs(int cpu)
   {
           unsigned long flags;
   
           local_irq_save(flags);
           if (rcu_qsctr_help(&rcu_bh_ctrlblk))
                   invoke_rcu_callbacks();
           local_irq_restore(flags);
   }
   
   /*
    * Check to see if the scheduling-clock interrupt came from an extended
    * quiescent state, and, if so, tell RCU about it.  This function must
    * be called from hardirq context.  It is normally called from the
    * scheduling-clock interrupt.
    */
   void rcu_check_callbacks(int cpu, int user)
   {
           if (user || rcu_is_cpu_rrupt_from_idle())
                   rcu_sched_qs(cpu);
           else if (!in_softirq())
                   rcu_bh_qs(cpu);
           rcu_preempt_check_callbacks();
   }
   
   /*
    * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
    * whose grace period has elapsed.
    */
   static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
   {
           char *rn = NULL;
           struct rcu_head *next, *list;
           unsigned long flags;
           RCU_TRACE(int cb_count = 0);
   
           /* If no RCU callbacks ready to invoke, just return. */
           if (&rcp->rcucblist == rcp->donetail) {
                   RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
                   RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
                                                 ACCESS_ONCE(rcp->rcucblist),
                                                 need_resched(),
                                                 is_idle_task(current),
                                                 rcu_is_callbacks_kthread()));
                   return;
           }
   
           /* Move the ready-to-invoke callbacks to a local list. */
           local_irq_save(flags);
           RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
           list = rcp->rcucblist;
           rcp->rcucblist = *rcp->donetail;
           *rcp->donetail = NULL;
           if (rcp->curtail == rcp->donetail)
                   rcp->curtail = &rcp->rcucblist;
           rcu_preempt_remove_callbacks(rcp);
           rcp->donetail = &rcp->rcucblist;
           local_irq_restore(flags);
   
           /* Invoke the callbacks on the local list. */
           RCU_TRACE(rn = rcp->name);
           while (list) {
                   next = list->next;
                   prefetch(next);
                   debug_rcu_head_unqueue(list);
                   local_bh_disable();
                   __rcu_reclaim(rn, list);
                   local_bh_enable();
                   list = next;
                   RCU_TRACE(cb_count++);
           }
           RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
           RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
                                         is_idle_task(current),
                                         rcu_is_callbacks_kthread()));
   }
   
   static void rcu_process_callbacks(struct softirq_action *unused)
   {
           __rcu_process_callbacks(&rcu_sched_ctrlblk);
           __rcu_process_callbacks(&rcu_bh_ctrlblk);
           rcu_preempt_process_callbacks();
   }
   
   /*
    * Wait for a grace period to elapse.  But it is illegal to invoke
    * synchronize_sched() from within an RCU read-side critical section.
    * Therefore, any legal call to synchronize_sched() is a quiescent
    * state, and so on a UP system, synchronize_sched() need do nothing.
    * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
    * benefits of doing might_sleep() to reduce latency.)
    *
    * Cool, huh?  (Due to Josh Triplett.)
    *
    * But we want to make this a static inline later.  The cond_resched()
    * currently makes this problematic.
    */
   void synchronize_sched(void)
   {
           rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
                              !lock_is_held(&rcu_lock_map) &&
                              !lock_is_held(&rcu_sched_lock_map),
                              "Illegal synchronize_sched() in RCU read-side critical section");
           cond_resched();
   }
   EXPORT_SYMBOL_GPL(synchronize_sched);
   
   /*
    * Helper function for call_rcu() and call_rcu_bh().
    */
   static void __call_rcu(struct rcu_head *head,
                          void (*func)(struct rcu_head *rcu),
                          struct rcu_ctrlblk *rcp)
   {
           unsigned long flags;
   
           debug_rcu_head_queue(head);
           head->func = func;
           head->next = NULL;
   
           local_irq_save(flags);
           *rcp->curtail = head;
           rcp->curtail = &head->next;
           RCU_TRACE(rcp->qlen++);
           local_irq_restore(flags);
   }
   
   /*
    * Post an RCU callback to be invoked after the end of an RCU-sched grace
    * period.  But since we have but one CPU, that would be after any
    * quiescent state.
    */
   void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
   {
           __call_rcu(head, func, &rcu_sched_ctrlblk);
   }
   EXPORT_SYMBOL_GPL(call_rcu_sched);
   
   /*
    * Post an RCU bottom-half callback to be invoked after any subsequent
    * quiescent state.
    */
   void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
   {
           __call_rcu(head, func, &rcu_bh_ctrlblk);
   }
   EXPORT_SYMBOL_GPL(call_rcu_bh);

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