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

     /*
      * Read-Copy Update mechanism for mutual exclusion
      *
      * 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, 2001
     *
     * Authors: Dipankar Sarma <dipankar@in.ibm.com>
     *          Manfred Spraul <manfred@colorfullife.com>
     *
     * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
     * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
     * Papers:
     * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
     * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
     *
     * For detailed explanation of Read-Copy Update mechanism see -
     *              http://lse.sourceforge.net/locking/rcupdate.html
     *
     */
    #include <linux/types.h>
    #include <linux/kernel.h>
    #include <linux/init.h>
    #include <linux/spinlock.h>
    #include <linux/smp.h>
    #include <linux/interrupt.h>
    #include <linux/sched.h>
    #include <linux/atomic.h>
    #include <linux/bitops.h>
    #include <linux/percpu.h>
    #include <linux/notifier.h>
    #include <linux/cpu.h>
    #include <linux/mutex.h>
    #include <linux/export.h>
    #include <linux/hardirq.h>
    #include <linux/delay.h>
    #include <linux/module.h>
    
    #define CREATE_TRACE_POINTS
    #include <trace/events/rcu.h>
    
    #include "rcu.h"
    
    module_param(rcu_expedited, int, 0);
    
    #ifdef CONFIG_PREEMPT_RCU
    
    /*
     * Preemptible RCU implementation for rcu_read_lock().
     * Just increment ->rcu_read_lock_nesting, shared state will be updated
     * if we block.
     */
    void __rcu_read_lock(void)
    {
            current->rcu_read_lock_nesting++;
            barrier();  /* critical section after entry code. */
    }
    EXPORT_SYMBOL_GPL(__rcu_read_lock);
    
    /*
     * Preemptible RCU implementation for rcu_read_unlock().
     * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
     * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
     * invoke rcu_read_unlock_special() to clean up after a context switch
     * in an RCU read-side critical section and other special cases.
     */
    void __rcu_read_unlock(void)
    {
            struct task_struct *t = current;
    
            if (t->rcu_read_lock_nesting != 1) {
                    --t->rcu_read_lock_nesting;
            } else {
                    barrier();  /* critical section before exit code. */
                    t->rcu_read_lock_nesting = INT_MIN;
    #ifdef CONFIG_PROVE_RCU_DELAY
                    udelay(10); /* Make preemption more probable. */
    #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
                    barrier();  /* assign before ->rcu_read_unlock_special load */
                    if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
                            rcu_read_unlock_special(t);
                    barrier();  /* ->rcu_read_unlock_special load before assign */
                    t->rcu_read_lock_nesting = 0;
            }
    #ifdef CONFIG_PROVE_LOCKING
            {
                    int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
   
                   WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
           }
   #endif /* #ifdef CONFIG_PROVE_LOCKING */
   }
   EXPORT_SYMBOL_GPL(__rcu_read_unlock);
   
   /*
    * Check for a task exiting while in a preemptible-RCU read-side
    * critical section, clean up if so.  No need to issue warnings,
    * as debug_check_no_locks_held() already does this if lockdep
    * is enabled.
    */
   void exit_rcu(void)
   {
           struct task_struct *t = current;
   
           if (likely(list_empty(&current->rcu_node_entry)))
                   return;
           t->rcu_read_lock_nesting = 1;
           barrier();
           t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
           __rcu_read_unlock();
   }
   
   #else /* #ifdef CONFIG_PREEMPT_RCU */
   
   void exit_rcu(void)
   {
   }
   
   #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
   
   #ifdef CONFIG_DEBUG_LOCK_ALLOC
   static struct lock_class_key rcu_lock_key;
   struct lockdep_map rcu_lock_map =
           STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
   EXPORT_SYMBOL_GPL(rcu_lock_map);
   
   static struct lock_class_key rcu_bh_lock_key;
   struct lockdep_map rcu_bh_lock_map =
           STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
   EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
   
   static struct lock_class_key rcu_sched_lock_key;
   struct lockdep_map rcu_sched_lock_map =
           STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
   EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
   #endif
   
   #ifdef CONFIG_DEBUG_LOCK_ALLOC
   
   int debug_lockdep_rcu_enabled(void)
   {
           return rcu_scheduler_active && debug_locks &&
                  current->lockdep_recursion == 0;
   }
   EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
   
   /**
    * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
    *
    * Check for bottom half being disabled, which covers both the
    * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
    * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
    * will show the situation.  This is useful for debug checks in functions
    * that require that they be called within an RCU read-side critical
    * section.
    *
    * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
    *
    * Note that rcu_read_lock() is disallowed if the CPU is either idle or
    * offline from an RCU perspective, so check for those as well.
    */
   int rcu_read_lock_bh_held(void)
   {
           if (!debug_lockdep_rcu_enabled())
                   return 1;
           if (rcu_is_cpu_idle())
                   return 0;
           if (!rcu_lockdep_current_cpu_online())
                   return 0;
           return in_softirq() || irqs_disabled();
   }
   EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
   
   #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
   
   struct rcu_synchronize {
           struct rcu_head head;
           struct completion completion;
   };
   
   /*
    * Awaken the corresponding synchronize_rcu() instance now that a
    * grace period has elapsed.
    */
   static void wakeme_after_rcu(struct rcu_head  *head)
   {
           struct rcu_synchronize *rcu;
   
           rcu = container_of(head, struct rcu_synchronize, head);
           complete(&rcu->completion);
   }
   
   void wait_rcu_gp(call_rcu_func_t crf)
   {
           struct rcu_synchronize rcu;
   
           init_rcu_head_on_stack(&rcu.head);
           init_completion(&rcu.completion);
           /* Will wake me after RCU finished. */
           crf(&rcu.head, wakeme_after_rcu);
           /* Wait for it. */
           wait_for_completion(&rcu.completion);
           destroy_rcu_head_on_stack(&rcu.head);
   }
   EXPORT_SYMBOL_GPL(wait_rcu_gp);
   
   #ifdef CONFIG_PROVE_RCU
   /*
    * wrapper function to avoid #include problems.
    */
   int rcu_my_thread_group_empty(void)
   {
           return thread_group_empty(current);
   }
   EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
   #endif /* #ifdef CONFIG_PROVE_RCU */
   
   #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
   static inline void debug_init_rcu_head(struct rcu_head *head)
   {
           debug_object_init(head, &rcuhead_debug_descr);
   }
   
   static inline void debug_rcu_head_free(struct rcu_head *head)
   {
           debug_object_free(head, &rcuhead_debug_descr);
   }
   
   /*
    * fixup_init is called when:
    * - an active object is initialized
    */
   static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
   {
           struct rcu_head *head = addr;
   
           switch (state) {
           case ODEBUG_STATE_ACTIVE:
                   /*
                    * Ensure that queued callbacks are all executed.
                    * If we detect that we are nested in a RCU read-side critical
                    * section, we should simply fail, otherwise we would deadlock.
                    * In !PREEMPT configurations, there is no way to tell if we are
                    * in a RCU read-side critical section or not, so we never
                    * attempt any fixup and just print a warning.
                    */
   #ifndef CONFIG_PREEMPT
                   WARN_ON_ONCE(1);
                   return 0;
   #endif
                   if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                       irqs_disabled()) {
                           WARN_ON_ONCE(1);
                           return 0;
                   }
                   rcu_barrier();
                   rcu_barrier_sched();
                   rcu_barrier_bh();
                   debug_object_init(head, &rcuhead_debug_descr);
                   return 1;
           default:
                   return 0;
           }
   }
   
   /*
    * fixup_activate is called when:
    * - an active object is activated
    * - an unknown object is activated (might be a statically initialized object)
    * Activation is performed internally by call_rcu().
    */
   static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
   {
           struct rcu_head *head = addr;
   
           switch (state) {
   
           case ODEBUG_STATE_NOTAVAILABLE:
                   /*
                    * This is not really a fixup. We just make sure that it is
                    * tracked in the object tracker.
                    */
                   debug_object_init(head, &rcuhead_debug_descr);
                   debug_object_activate(head, &rcuhead_debug_descr);
                   return 0;
   
           case ODEBUG_STATE_ACTIVE:
                   /*
                    * Ensure that queued callbacks are all executed.
                    * If we detect that we are nested in a RCU read-side critical
                    * section, we should simply fail, otherwise we would deadlock.
                    * In !PREEMPT configurations, there is no way to tell if we are
                    * in a RCU read-side critical section or not, so we never
                    * attempt any fixup and just print a warning.
                    */
   #ifndef CONFIG_PREEMPT
                   WARN_ON_ONCE(1);
                   return 0;
   #endif
                   if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                       irqs_disabled()) {
                           WARN_ON_ONCE(1);
                           return 0;
                   }
                   rcu_barrier();
                   rcu_barrier_sched();
                   rcu_barrier_bh();
                   debug_object_activate(head, &rcuhead_debug_descr);
                   return 1;
           default:
                   return 0;
           }
   }
   
   /*
    * fixup_free is called when:
    * - an active object is freed
    */
   static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
   {
           struct rcu_head *head = addr;
   
           switch (state) {
           case ODEBUG_STATE_ACTIVE:
                   /*
                    * Ensure that queued callbacks are all executed.
                    * If we detect that we are nested in a RCU read-side critical
                    * section, we should simply fail, otherwise we would deadlock.
                    * In !PREEMPT configurations, there is no way to tell if we are
                    * in a RCU read-side critical section or not, so we never
                    * attempt any fixup and just print a warning.
                    */
   #ifndef CONFIG_PREEMPT
                   WARN_ON_ONCE(1);
                   return 0;
   #endif
                   if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                       irqs_disabled()) {
                           WARN_ON_ONCE(1);
                           return 0;
                   }
                   rcu_barrier();
                   rcu_barrier_sched();
                   rcu_barrier_bh();
                   debug_object_free(head, &rcuhead_debug_descr);
                   return 1;
           default:
                   return 0;
           }
   }
   
   /**
    * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
    * @head: pointer to rcu_head structure to be initialized
    *
    * This function informs debugobjects of a new rcu_head structure that
    * has been allocated as an auto variable on the stack.  This function
    * is not required for rcu_head structures that are statically defined or
    * that are dynamically allocated on the heap.  This function has no
    * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
    */
   void init_rcu_head_on_stack(struct rcu_head *head)
   {
           debug_object_init_on_stack(head, &rcuhead_debug_descr);
   }
   EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
   
   /**
    * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
    * @head: pointer to rcu_head structure to be initialized
    *
    * This function informs debugobjects that an on-stack rcu_head structure
    * is about to go out of scope.  As with init_rcu_head_on_stack(), this
    * function is not required for rcu_head structures that are statically
    * defined or that are dynamically allocated on the heap.  Also as with
    * init_rcu_head_on_stack(), this function has no effect for
    * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
    */
   void destroy_rcu_head_on_stack(struct rcu_head *head)
   {
           debug_object_free(head, &rcuhead_debug_descr);
   }
   EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
   
   struct debug_obj_descr rcuhead_debug_descr = {
           .name = "rcu_head",
           .fixup_init = rcuhead_fixup_init,
           .fixup_activate = rcuhead_fixup_activate,
           .fixup_free = rcuhead_fixup_free,
   };
   EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
   #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
   
   #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
   void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
   {
           trace_rcu_torture_read(rcutorturename, rhp);
   }
   EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
   #else
   #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
   #endif

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