FreeBSD/Linux Kernel Cross Reference
sys/kernel/rcutree.h

     /*
      * Read-Copy Update mechanism for mutual exclusion (tree-based version)
      * Internal non-public definitions.
      *
      * 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: Ingo Molnar <mingo@elte.hu>
     *         Paul E. McKenney <paulmck@linux.vnet.ibm.com>
     */
    
    #include <linux/cache.h>
    #include <linux/spinlock.h>
    #include <linux/threads.h>
    #include <linux/cpumask.h>
    #include <linux/seqlock.h>
    
    /*
     * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
     * CONFIG_RCU_FANOUT_LEAF.
     * In theory, it should be possible to add more levels straightforwardly.
     * In practice, this did work well going from three levels to four.
     * Of course, your mileage may vary.
     */
    #define MAX_RCU_LVLS 4
    #define RCU_FANOUT_1          (CONFIG_RCU_FANOUT_LEAF)
    #define RCU_FANOUT_2          (RCU_FANOUT_1 * CONFIG_RCU_FANOUT)
    #define RCU_FANOUT_3          (RCU_FANOUT_2 * CONFIG_RCU_FANOUT)
    #define RCU_FANOUT_4          (RCU_FANOUT_3 * CONFIG_RCU_FANOUT)
    
    #if NR_CPUS <= RCU_FANOUT_1
    #  define RCU_NUM_LVLS        1
    #  define NUM_RCU_LVL_0       1
    #  define NUM_RCU_LVL_1       (NR_CPUS)
    #  define NUM_RCU_LVL_2       0
    #  define NUM_RCU_LVL_3       0
    #  define NUM_RCU_LVL_4       0
    #elif NR_CPUS <= RCU_FANOUT_2
    #  define RCU_NUM_LVLS        2
    #  define NUM_RCU_LVL_0       1
    #  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
    #  define NUM_RCU_LVL_2       (NR_CPUS)
    #  define NUM_RCU_LVL_3       0
    #  define NUM_RCU_LVL_4       0
    #elif NR_CPUS <= RCU_FANOUT_3
    #  define RCU_NUM_LVLS        3
    #  define NUM_RCU_LVL_0       1
    #  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
    #  define NUM_RCU_LVL_2       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
    #  define NUM_RCU_LVL_3       (NR_CPUS)
    #  define NUM_RCU_LVL_4       0
    #elif NR_CPUS <= RCU_FANOUT_4
    #  define RCU_NUM_LVLS        4
    #  define NUM_RCU_LVL_0       1
    #  define NUM_RCU_LVL_1       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_3)
    #  define NUM_RCU_LVL_2       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_2)
    #  define NUM_RCU_LVL_3       DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_1)
    #  define NUM_RCU_LVL_4       (NR_CPUS)
    #else
    # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
    #endif /* #if (NR_CPUS) <= RCU_FANOUT_1 */
    
    #define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3 + NUM_RCU_LVL_4)
    #define NUM_RCU_NODES (RCU_SUM - NR_CPUS)
    
    extern int rcu_num_lvls;
    extern int rcu_num_nodes;
    
    /*
     * Dynticks per-CPU state.
     */
    struct rcu_dynticks {
            long long dynticks_nesting; /* Track irq/process nesting level. */
                                        /* Process level is worth LLONG_MAX/2. */
            int dynticks_nmi_nesting;   /* Track NMI nesting level. */
            atomic_t dynticks;          /* Even value for idle, else odd. */
    #ifdef CONFIG_RCU_FAST_NO_HZ
            int dyntick_drain;          /* Prepare-for-idle state variable. */
            unsigned long dyntick_holdoff;
                                        /* No retries for the jiffy of failure. */
            struct timer_list idle_gp_timer;
                                        /* Wake up CPU sleeping with callbacks. */
            unsigned long idle_gp_timer_expires;
                                        /* When to wake up CPU (for repost). */
            bool idle_first_pass;       /* First pass of attempt to go idle? */
            unsigned long nonlazy_posted;
                                       /* # times non-lazy CBs posted to CPU. */
           unsigned long nonlazy_posted_snap;
                                       /* idle-period nonlazy_posted snapshot. */
           int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */
   #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
   #ifdef CONFIG_RCU_USER_QS
           bool ignore_user_qs;        /* Treat userspace as extended QS or not */
           bool in_user;               /* Is the CPU in userland from RCU POV? */
   #endif
   };
   
   /* RCU's kthread states for tracing. */
   #define RCU_KTHREAD_STOPPED  0
   #define RCU_KTHREAD_RUNNING  1
   #define RCU_KTHREAD_WAITING  2
   #define RCU_KTHREAD_OFFCPU   3
   #define RCU_KTHREAD_YIELDING 4
   #define RCU_KTHREAD_MAX      4
   
   /*
    * Definition for node within the RCU grace-period-detection hierarchy.
    */
   struct rcu_node {
           raw_spinlock_t lock;    /* Root rcu_node's lock protects some */
                                   /*  rcu_state fields as well as following. */
           unsigned long gpnum;    /* Current grace period for this node. */
                                   /*  This will either be equal to or one */
                                   /*  behind the root rcu_node's gpnum. */
           unsigned long completed; /* Last GP completed for this node. */
                                   /*  This will either be equal to or one */
                                   /*  behind the root rcu_node's gpnum. */
           unsigned long qsmask;   /* CPUs or groups that need to switch in */
                                   /*  order for current grace period to proceed.*/
                                   /*  In leaf rcu_node, each bit corresponds to */
                                   /*  an rcu_data structure, otherwise, each */
                                   /*  bit corresponds to a child rcu_node */
                                   /*  structure. */
           unsigned long expmask;  /* Groups that have ->blkd_tasks */
                                   /*  elements that need to drain to allow the */
                                   /*  current expedited grace period to */
                                   /*  complete (only for TREE_PREEMPT_RCU). */
           atomic_t wakemask;      /* CPUs whose kthread needs to be awakened. */
                                   /*  Since this has meaning only for leaf */
                                   /*  rcu_node structures, 32 bits suffices. */
           unsigned long qsmaskinit;
                                   /* Per-GP initial value for qsmask & expmask. */
           unsigned long grpmask;  /* Mask to apply to parent qsmask. */
                                   /*  Only one bit will be set in this mask. */
           int     grplo;          /* lowest-numbered CPU or group here. */
           int     grphi;          /* highest-numbered CPU or group here. */
           u8      grpnum;         /* CPU/group number for next level up. */
           u8      level;          /* root is at level 0. */
           struct rcu_node *parent;
           struct list_head blkd_tasks;
                                   /* Tasks blocked in RCU read-side critical */
                                   /*  section.  Tasks are placed at the head */
                                   /*  of this list and age towards the tail. */
           struct list_head *gp_tasks;
                                   /* Pointer to the first task blocking the */
                                   /*  current grace period, or NULL if there */
                                   /*  is no such task. */
           struct list_head *exp_tasks;
                                   /* Pointer to the first task blocking the */
                                   /*  current expedited grace period, or NULL */
                                   /*  if there is no such task.  If there */
                                   /*  is no current expedited grace period, */
                                   /*  then there can cannot be any such task. */
   #ifdef CONFIG_RCU_BOOST
           struct list_head *boost_tasks;
                                   /* Pointer to first task that needs to be */
                                   /*  priority boosted, or NULL if no priority */
                                   /*  boosting is needed for this rcu_node */
                                   /*  structure.  If there are no tasks */
                                   /*  queued on this rcu_node structure that */
                                   /*  are blocking the current grace period, */
                                   /*  there can be no such task. */
           unsigned long boost_time;
                                   /* When to start boosting (jiffies). */
           struct task_struct *boost_kthread_task;
                                   /* kthread that takes care of priority */
                                   /*  boosting for this rcu_node structure. */
           unsigned int boost_kthread_status;
                                   /* State of boost_kthread_task for tracing. */
           unsigned long n_tasks_boosted;
                                   /* Total number of tasks boosted. */
           unsigned long n_exp_boosts;
                                   /* Number of tasks boosted for expedited GP. */
           unsigned long n_normal_boosts;
                                   /* Number of tasks boosted for normal GP. */
           unsigned long n_balk_blkd_tasks;
                                   /* Refused to boost: no blocked tasks. */
           unsigned long n_balk_exp_gp_tasks;
                                   /* Refused to boost: nothing blocking GP. */
           unsigned long n_balk_boost_tasks;
                                   /* Refused to boost: already boosting. */
           unsigned long n_balk_notblocked;
                                   /* Refused to boost: RCU RS CS still running. */
           unsigned long n_balk_notyet;
                                   /* Refused to boost: not yet time. */
           unsigned long n_balk_nos;
                                   /* Refused to boost: not sure why, though. */
                                   /*  This can happen due to race conditions. */
   #endif /* #ifdef CONFIG_RCU_BOOST */
           raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
   } ____cacheline_internodealigned_in_smp;
   
   /*
    * Do a full breadth-first scan of the rcu_node structures for the
    * specified rcu_state structure.
    */
   #define rcu_for_each_node_breadth_first(rsp, rnp) \
           for ((rnp) = &(rsp)->node[0]; \
                (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
   
   /*
    * Do a breadth-first scan of the non-leaf rcu_node structures for the
    * specified rcu_state structure.  Note that if there is a singleton
    * rcu_node tree with but one rcu_node structure, this loop is a no-op.
    */
   #define rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) \
           for ((rnp) = &(rsp)->node[0]; \
                (rnp) < (rsp)->level[rcu_num_lvls - 1]; (rnp)++)
   
   /*
    * Scan the leaves of the rcu_node hierarchy for the specified rcu_state
    * structure.  Note that if there is a singleton rcu_node tree with but
    * one rcu_node structure, this loop -will- visit the rcu_node structure.
    * It is still a leaf node, even if it is also the root node.
    */
   #define rcu_for_each_leaf_node(rsp, rnp) \
           for ((rnp) = (rsp)->level[rcu_num_lvls - 1]; \
                (rnp) < &(rsp)->node[rcu_num_nodes]; (rnp)++)
   
   /* Index values for nxttail array in struct rcu_data. */
   #define RCU_DONE_TAIL           0       /* Also RCU_WAIT head. */
   #define RCU_WAIT_TAIL           1       /* Also RCU_NEXT_READY head. */
   #define RCU_NEXT_READY_TAIL     2       /* Also RCU_NEXT head. */
   #define RCU_NEXT_TAIL           3
   #define RCU_NEXT_SIZE           4
   
   /* Per-CPU data for read-copy update. */
   struct rcu_data {
           /* 1) quiescent-state and grace-period handling : */
           unsigned long   completed;      /* Track rsp->completed gp number */
                                           /*  in order to detect GP end. */
           unsigned long   gpnum;          /* Highest gp number that this CPU */
                                           /*  is aware of having started. */
           bool            passed_quiesce; /* User-mode/idle loop etc. */
           bool            qs_pending;     /* Core waits for quiesc state. */
           bool            beenonline;     /* CPU online at least once. */
           bool            preemptible;    /* Preemptible RCU? */
           struct rcu_node *mynode;        /* This CPU's leaf of hierarchy */
           unsigned long grpmask;          /* Mask to apply to leaf qsmask. */
   #ifdef CONFIG_RCU_CPU_STALL_INFO
           unsigned long   ticks_this_gp;  /* The number of scheduling-clock */
                                           /*  ticks this CPU has handled */
                                           /*  during and after the last grace */
                                           /* period it is aware of. */
   #endif /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
   
           /* 2) batch handling */
           /*
            * If nxtlist is not NULL, it is partitioned as follows.
            * Any of the partitions might be empty, in which case the
            * pointer to that partition will be equal to the pointer for
            * the following partition.  When the list is empty, all of
            * the nxttail elements point to the ->nxtlist pointer itself,
            * which in that case is NULL.
            *
            * [nxtlist, *nxttail[RCU_DONE_TAIL]):
            *      Entries that batch # <= ->completed
            *      The grace period for these entries has completed, and
            *      the other grace-period-completed entries may be moved
            *      here temporarily in rcu_process_callbacks().
            * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
            *      Entries that batch # <= ->completed - 1: waiting for current GP
            * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
            *      Entries known to have arrived before current GP ended
            * [*nxttail[RCU_NEXT_READY_TAIL], *nxttail[RCU_NEXT_TAIL]):
            *      Entries that might have arrived after current GP ended
            *      Note that the value of *nxttail[RCU_NEXT_TAIL] will
            *      always be NULL, as this is the end of the list.
            */
           struct rcu_head *nxtlist;
           struct rcu_head **nxttail[RCU_NEXT_SIZE];
           long            qlen_lazy;      /* # of lazy queued callbacks */
           long            qlen;           /* # of queued callbacks, incl lazy */
           long            qlen_last_fqs_check;
                                           /* qlen at last check for QS forcing */
           unsigned long   n_cbs_invoked;  /* count of RCU cbs invoked. */
           unsigned long   n_nocbs_invoked; /* count of no-CBs RCU cbs invoked. */
           unsigned long   n_cbs_orphaned; /* RCU cbs orphaned by dying CPU */
           unsigned long   n_cbs_adopted;  /* RCU cbs adopted from dying CPU */
           unsigned long   n_force_qs_snap;
                                           /* did other CPU force QS recently? */
           long            blimit;         /* Upper limit on a processed batch */
   
           /* 3) dynticks interface. */
           struct rcu_dynticks *dynticks;  /* Shared per-CPU dynticks state. */
           int dynticks_snap;              /* Per-GP tracking for dynticks. */
   
           /* 4) reasons this CPU needed to be kicked by force_quiescent_state */
           unsigned long dynticks_fqs;     /* Kicked due to dynticks idle. */
           unsigned long offline_fqs;      /* Kicked due to being offline. */
   
           /* 5) __rcu_pending() statistics. */
           unsigned long n_rcu_pending;    /* rcu_pending() calls since boot. */
           unsigned long n_rp_qs_pending;
           unsigned long n_rp_report_qs;
           unsigned long n_rp_cb_ready;
           unsigned long n_rp_cpu_needs_gp;
           unsigned long n_rp_gp_completed;
           unsigned long n_rp_gp_started;
           unsigned long n_rp_need_nothing;
   
           /* 6) _rcu_barrier() and OOM callbacks. */
           struct rcu_head barrier_head;
   #ifdef CONFIG_RCU_FAST_NO_HZ
           struct rcu_head oom_head;
   #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
   
           /* 7) Callback offloading. */
   #ifdef CONFIG_RCU_NOCB_CPU
           struct rcu_head *nocb_head;     /* CBs waiting for kthread. */
           struct rcu_head **nocb_tail;
           atomic_long_t nocb_q_count;     /* # CBs waiting for kthread */
           atomic_long_t nocb_q_count_lazy; /*  (approximate). */
           int nocb_p_count;               /* # CBs being invoked by kthread */
           int nocb_p_count_lazy;          /*  (approximate). */
           wait_queue_head_t nocb_wq;      /* For nocb kthreads to sleep on. */
           struct task_struct *nocb_kthread;
   #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
   
           int cpu;
           struct rcu_state *rsp;
   };
   
   /* Values for fqs_state field in struct rcu_state. */
   #define RCU_GP_IDLE             0       /* No grace period in progress. */
   #define RCU_GP_INIT             1       /* Grace period being initialized. */
   #define RCU_SAVE_DYNTICK        2       /* Need to scan dyntick state. */
   #define RCU_FORCE_QS            3       /* Need to force quiescent state. */
   #define RCU_SIGNAL_INIT         RCU_SAVE_DYNTICK
   
   #define RCU_JIFFIES_TILL_FORCE_QS        3      /* for rsp->jiffies_force_qs */
   
   #ifdef CONFIG_PROVE_RCU
   #define RCU_STALL_DELAY_DELTA          (5 * HZ)
   #else
   #define RCU_STALL_DELAY_DELTA          0
   #endif
   #define RCU_STALL_RAT_DELAY             2       /* Allow other CPUs time */
                                                   /*  to take at least one */
                                                   /*  scheduling clock irq */
                                                   /*  before ratting on them. */
   
   #define rcu_wait(cond)                                                  \
   do {                                                                    \
           for (;;) {                                                      \
                   set_current_state(TASK_INTERRUPTIBLE);                  \
                   if (cond)                                               \
                           break;                                          \
                   schedule();                                             \
           }                                                               \
           __set_current_state(TASK_RUNNING);                              \
   } while (0)
   
   /*
    * RCU global state, including node hierarchy.  This hierarchy is
    * represented in "heap" form in a dense array.  The root (first level)
    * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
    * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
    * and the third level in ->node[m+1] and following (->node[m+1] referenced
    * by ->level[2]).  The number of levels is determined by the number of
    * CPUs and by CONFIG_RCU_FANOUT.  Small systems will have a "hierarchy"
    * consisting of a single rcu_node.
    */
   struct rcu_state {
           struct rcu_node node[NUM_RCU_NODES];    /* Hierarchy. */
           struct rcu_node *level[RCU_NUM_LVLS];   /* Hierarchy levels. */
           u32 levelcnt[MAX_RCU_LVLS + 1];         /* # nodes in each level. */
           u8 levelspread[RCU_NUM_LVLS];           /* kids/node in each level. */
           struct rcu_data __percpu *rda;          /* pointer of percu rcu_data. */
           void (*call)(struct rcu_head *head,     /* call_rcu() flavor. */
                        void (*func)(struct rcu_head *head));
   #ifdef CONFIG_RCU_NOCB_CPU
           void (*call_remote)(struct rcu_head *head,
                        void (*func)(struct rcu_head *head));
                                                   /* call_rcu() flavor, but for */
                                                   /*  placing on remote CPU. */
   #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
   
           /* The following fields are guarded by the root rcu_node's lock. */
   
           u8      fqs_state ____cacheline_internodealigned_in_smp;
                                                   /* Force QS state. */
           u8      boost;                          /* Subject to priority boost. */
           unsigned long gpnum;                    /* Current gp number. */
           unsigned long completed;                /* # of last completed gp. */
           struct task_struct *gp_kthread;         /* Task for grace periods. */
           wait_queue_head_t gp_wq;                /* Where GP task waits. */
           int gp_flags;                           /* Commands for GP task. */
   
           /* End of fields guarded by root rcu_node's lock. */
   
           raw_spinlock_t orphan_lock ____cacheline_internodealigned_in_smp;
                                                   /* Protect following fields. */
           struct rcu_head *orphan_nxtlist;        /* Orphaned callbacks that */
                                                   /*  need a grace period. */
           struct rcu_head **orphan_nxttail;       /* Tail of above. */
           struct rcu_head *orphan_donelist;       /* Orphaned callbacks that */
                                                   /*  are ready to invoke. */
           struct rcu_head **orphan_donetail;      /* Tail of above. */
           long qlen_lazy;                         /* Number of lazy callbacks. */
           long qlen;                              /* Total number of callbacks. */
           /* End of fields guarded by orphan_lock. */
   
           struct mutex onoff_mutex;               /* Coordinate hotplug & GPs. */
   
           struct mutex barrier_mutex;             /* Guards barrier fields. */
           atomic_t barrier_cpu_count;             /* # CPUs waiting on. */
           struct completion barrier_completion;   /* Wake at barrier end. */
           unsigned long n_barrier_done;           /* ++ at start and end of */
                                                   /*  _rcu_barrier(). */
           /* End of fields guarded by barrier_mutex. */
   
           atomic_long_t expedited_start;          /* Starting ticket. */
           atomic_long_t expedited_done;           /* Done ticket. */
           atomic_long_t expedited_wrap;           /* # near-wrap incidents. */
           atomic_long_t expedited_tryfail;        /* # acquisition failures. */
           atomic_long_t expedited_workdone1;      /* # done by others #1. */
           atomic_long_t expedited_workdone2;      /* # done by others #2. */
           atomic_long_t expedited_normal;         /* # fallbacks to normal. */
           atomic_long_t expedited_stoppedcpus;    /* # successful stop_cpus. */
           atomic_long_t expedited_done_tries;     /* # tries to update _done. */
           atomic_long_t expedited_done_lost;      /* # times beaten to _done. */
           atomic_long_t expedited_done_exit;      /* # times exited _done loop. */
   
           unsigned long jiffies_force_qs;         /* Time at which to invoke */
                                                   /*  force_quiescent_state(). */
           unsigned long n_force_qs;               /* Number of calls to */
                                                   /*  force_quiescent_state(). */
           unsigned long n_force_qs_lh;            /* ~Number of calls leaving */
                                                   /*  due to lock unavailable. */
           unsigned long n_force_qs_ngp;           /* Number of calls leaving */
                                                   /*  due to no GP active. */
           unsigned long gp_start;                 /* Time at which GP started, */
                                                   /*  but in jiffies. */
           unsigned long jiffies_stall;            /* Time at which to check */
                                                   /*  for CPU stalls. */
           unsigned long gp_max;                   /* Maximum GP duration in */
                                                   /*  jiffies. */
           char *name;                             /* Name of structure. */
           struct list_head flavors;               /* List of RCU flavors. */
   };
   
   /* Values for rcu_state structure's gp_flags field. */
   #define RCU_GP_FLAG_INIT 0x1    /* Need grace-period initialization. */
   #define RCU_GP_FLAG_FQS  0x2    /* Need grace-period quiescent-state forcing. */
   
   extern struct list_head rcu_struct_flavors;
   
   /* Sequence through rcu_state structures for each RCU flavor. */
   #define for_each_rcu_flavor(rsp) \
           list_for_each_entry((rsp), &rcu_struct_flavors, flavors)
   
   /* Return values for rcu_preempt_offline_tasks(). */
   
   #define RCU_OFL_TASKS_NORM_GP   0x1             /* Tasks blocking normal */
                                                   /*  GP were moved to root. */
   #define RCU_OFL_TASKS_EXP_GP    0x2             /* Tasks blocking expedited */
                                                   /*  GP were moved to root. */
   
   /*
    * RCU implementation internal declarations:
    */
   extern struct rcu_state rcu_sched_state;
   DECLARE_PER_CPU(struct rcu_data, rcu_sched_data);
   
   extern struct rcu_state rcu_bh_state;
   DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
   
   #ifdef CONFIG_TREE_PREEMPT_RCU
   extern struct rcu_state rcu_preempt_state;
   DECLARE_PER_CPU(struct rcu_data, rcu_preempt_data);
   #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
   
   #ifdef CONFIG_RCU_BOOST
   DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
   DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);
   DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
   DECLARE_PER_CPU(char, rcu_cpu_has_work);
   #endif /* #ifdef CONFIG_RCU_BOOST */
   
   #ifndef RCU_TREE_NONCORE
   
   /* Forward declarations for rcutree_plugin.h */
   static void rcu_bootup_announce(void);
   long rcu_batches_completed(void);
   static void rcu_preempt_note_context_switch(int cpu);
   static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
   #ifdef CONFIG_HOTPLUG_CPU
   static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
                                         unsigned long flags);
   #endif /* #ifdef CONFIG_HOTPLUG_CPU */
   static void rcu_print_detail_task_stall(struct rcu_state *rsp);
   static int rcu_print_task_stall(struct rcu_node *rnp);
   static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
   #ifdef CONFIG_HOTPLUG_CPU
   static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
                                        struct rcu_node *rnp,
                                        struct rcu_data *rdp);
   #endif /* #ifdef CONFIG_HOTPLUG_CPU */
   static void rcu_preempt_check_callbacks(int cpu);
   void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
   #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU)
   static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
                                  bool wake);
   #endif /* #if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU) */
   static void __init __rcu_init_preempt(void);
   static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
   static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
   static void invoke_rcu_callbacks_kthread(void);
   static bool rcu_is_callbacks_kthread(void);
   #ifdef CONFIG_RCU_BOOST
   static void rcu_preempt_do_callbacks(void);
   static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
                                                    struct rcu_node *rnp);
   #endif /* #ifdef CONFIG_RCU_BOOST */
   static void __cpuinit rcu_prepare_kthreads(int cpu);
   static void rcu_prepare_for_idle_init(int cpu);
   static void rcu_cleanup_after_idle(int cpu);
   static void rcu_prepare_for_idle(int cpu);
   static void rcu_idle_count_callbacks_posted(void);
   static void print_cpu_stall_info_begin(void);
   static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);
   static void print_cpu_stall_info_end(void);
   static void zero_cpu_stall_ticks(struct rcu_data *rdp);
   static void increment_cpu_stall_ticks(void);
   static bool is_nocb_cpu(int cpu);
   static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
                               bool lazy);
   static bool rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
                                         struct rcu_data *rdp);
   static bool nocb_cpu_expendable(int cpu);
   static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
   static void rcu_spawn_nocb_kthreads(struct rcu_state *rsp);
   static void init_nocb_callback_list(struct rcu_data *rdp);
   static void __init rcu_init_nocb(void);
   
   #endif /* #ifndef RCU_TREE_NONCORE */
   
   #ifdef CONFIG_RCU_TRACE
   #ifdef CONFIG_RCU_NOCB_CPU
   /* Sum up queue lengths for tracing. */
   static inline void rcu_nocb_q_lengths(struct rcu_data *rdp, long *ql, long *qll)
   {
           *ql = atomic_long_read(&rdp->nocb_q_count) + rdp->nocb_p_count;
           *qll = atomic_long_read(&rdp->nocb_q_count_lazy) + rdp->nocb_p_count_lazy;
   }
   #else /* #ifdef CONFIG_RCU_NOCB_CPU */
   static inline void rcu_nocb_q_lengths(struct rcu_data *rdp, long *ql, long *qll)
   {
           *ql = 0;
           *qll = 0;
   }
   #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
   #endif /* #ifdef CONFIG_RCU_TRACE */

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