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   /*
    * 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,
                                unsigned long secs,
                                unsigned long c_old, unsigned long c)
 {
         trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
 }
 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 #else
 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
         do { } while (0)
 #endif
 
 #ifdef CONFIG_RCU_STALL_COMMON
 
 #ifdef CONFIG_PROVE_RCU
 #define RCU_STALL_DELAY_DELTA          (5 * HZ)
 #else
 #define RCU_STALL_DELAY_DELTA          0
 #endif
 
 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
 int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
 
 module_param(rcu_cpu_stall_suppress, int, 0644);
 module_param(rcu_cpu_stall_timeout, int, 0644);
 
 int rcu_jiffies_till_stall_check(void)
 {
         int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
 
         /*
          * Limit check must be consistent with the Kconfig limits
          * for CONFIG_RCU_CPU_STALL_TIMEOUT.
          */
         if (till_stall_check < 3) {
                 ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
                 till_stall_check = 3;
         } else if (till_stall_check > 300) {
                 ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
                 till_stall_check = 300;
         }
         return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
 }
 
 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
 {
         rcu_cpu_stall_suppress = 1;
         return NOTIFY_DONE;
 }
 
 static struct notifier_block rcu_panic_block = {
         .notifier_call = rcu_panic,
 };
 
 static int __init check_cpu_stall_init(void)
 {
         atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
         return 0;
 }
 early_initcall(check_cpu_stall_init);
 
 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
 

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