LXR linux/kernel/rcu/srcutiny.c

   1/*
   2 * Sleepable Read-Copy Update mechanism for mutual exclusion,
   3 *      tiny version for non-preemptible single-CPU use.
   4 *
   5 * This program is free software; you can redistribute it and/or modify
   6 * it under the terms of the GNU General Public License as published by
   7 * the Free Software Foundation; either version 2 of the License, or
   8 * (at your option) any later version.
   9 *
  10 * This program is distributed in the hope that it will be useful,
  11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 * GNU General Public License for more details.
  14 *
  15 * You should have received a copy of the GNU General Public License
  16 * along with this program; if not, you can access it online at
  17 * http://www.gnu.org/licenses/gpl-2.0.html.
  18 *
  19 * Copyright (C) IBM Corporation, 2017
  20 *
  21 * Author: Paul McKenney <paulmck@us.ibm.com>
  22 */
  23
  24#include <linux/export.h>
  25#include <linux/mutex.h>
  26#include <linux/preempt.h>
  27#include <linux/rcupdate_wait.h>
  28#include <linux/sched.h>
  29#include <linux/delay.h>
  30#include <linux/srcu.h>
  31
  32#include <linux/rcu_node_tree.h>
  33#include "rcu_segcblist.h"
  34#include "rcu.h"
  35
  36int rcu_scheduler_active __read_mostly;
  37
  38static int init_srcu_struct_fields(struct srcu_struct *sp)
  39{
  40        sp->srcu_lock_nesting[0] = 0;
  41        sp->srcu_lock_nesting[1] = 0;
  42        init_swait_queue_head(&sp->srcu_wq);
  43        sp->srcu_cb_head = NULL;
  44        sp->srcu_cb_tail = &sp->srcu_cb_head;
  45        sp->srcu_gp_running = false;
  46        sp->srcu_gp_waiting = false;
  47        sp->srcu_idx = 0;
  48        INIT_WORK(&sp->srcu_work, srcu_drive_gp);
  49        return 0;
  50}
  51
  52#ifdef CONFIG_DEBUG_LOCK_ALLOC
  53
  54int __init_srcu_struct(struct srcu_struct *sp, const char *name,
  55                       struct lock_class_key *key)
  56{
  57        /* Don't re-initialize a lock while it is held. */
  58        debug_check_no_locks_freed((void *)sp, sizeof(*sp));
  59        lockdep_init_map(&sp->dep_map, name, key, 0);
  60        return init_srcu_struct_fields(sp);
  61}
  62EXPORT_SYMBOL_GPL(__init_srcu_struct);
  63
  64#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  65
  66/*
  67 * init_srcu_struct - initialize a sleep-RCU structure
  68 * @sp: structure to initialize.
  69 *
  70 * Must invoke this on a given srcu_struct before passing that srcu_struct
  71 * to any other function.  Each srcu_struct represents a separate domain
  72 * of SRCU protection.
  73 */
  74int init_srcu_struct(struct srcu_struct *sp)
  75{
  76        return init_srcu_struct_fields(sp);
  77}
  78EXPORT_SYMBOL_GPL(init_srcu_struct);
  79
  80#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  81
  82/*
  83 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  84 * @sp: structure to clean up.
  85 *
  86 * Must invoke this after you are finished using a given srcu_struct that
  87 * was initialized via init_srcu_struct(), else you leak memory.
  88 */
  89void cleanup_srcu_struct(struct srcu_struct *sp)
  90{
  91        WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
  92        flush_work(&sp->srcu_work);
  93        WARN_ON(sp->srcu_gp_running);
  94        WARN_ON(sp->srcu_gp_waiting);
  95        WARN_ON(sp->srcu_cb_head);
  96        WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
  97}
  98EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
  99
 100/*
 101 * Removes the count for the old reader from the appropriate element of
 102 * the srcu_struct.
 103 */
 104void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 105{
 106        int newval = sp->srcu_lock_nesting[idx] - 1;
 107
 108        WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
 109        if (!newval && READ_ONCE(sp->srcu_gp_waiting))
 110                swake_up(&sp->srcu_wq);
 111}
 112EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 113
 114/*
 115 * Workqueue handler to drive one grace period and invoke any callbacks
 116 * that become ready as a result.  Single-CPU and !PREEMPT operation
 117 * means that we get away with murder on synchronization.  ;-)
 118 */
 119void srcu_drive_gp(struct work_struct *wp)
 120{
 121        int idx;
 122        struct rcu_head *lh;
 123        struct rcu_head *rhp;
 124        struct srcu_struct *sp;
 125
 126        sp = container_of(wp, struct srcu_struct, srcu_work);
 127        if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head))
 128                return; /* Already running or nothing to do. */
 129
 130        /* Remove recently arrived callbacks and wait for readers. */
 131        WRITE_ONCE(sp->srcu_gp_running, true);
 132        local_irq_disable();
 133        lh = sp->srcu_cb_head;
 134        sp->srcu_cb_head = NULL;
 135        sp->srcu_cb_tail = &sp->srcu_cb_head;
 136        local_irq_enable();
 137        idx = sp->srcu_idx;
 138        WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
 139        WRITE_ONCE(sp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 140        swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
 141        WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
 142
 143        /* Invoke the callbacks we removed above. */
 144        while (lh) {
 145                rhp = lh;
 146                lh = lh->next;
 147                local_bh_disable();
 148                rhp->func(rhp);
 149                local_bh_enable();
 150        }
 151
 152        /*
 153         * Enable rescheduling, and if there are more callbacks,
 154         * reschedule ourselves.  This can race with a call_srcu()
 155         * at interrupt level, but the ->srcu_gp_running checks will
 156         * straighten that out.
 157         */
 158        WRITE_ONCE(sp->srcu_gp_running, false);
 159        if (READ_ONCE(sp->srcu_cb_head))
 160                schedule_work(&sp->srcu_work);
 161}
 162EXPORT_SYMBOL_GPL(srcu_drive_gp);
 163
 164/*
 165 * Enqueue an SRCU callback on the specified srcu_struct structure,
 166 * initiating grace-period processing if it is not already running.
 167 */
 168void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
 169               rcu_callback_t func)
 170{
 171        unsigned long flags;
 172
 173        rhp->func = func;
 174        rhp->next = NULL;
 175        local_irq_save(flags);
 176        *sp->srcu_cb_tail = rhp;
 177        sp->srcu_cb_tail = &rhp->next;
 178        local_irq_restore(flags);
 179        if (!READ_ONCE(sp->srcu_gp_running))
 180                schedule_work(&sp->srcu_work);
 181}
 182EXPORT_SYMBOL_GPL(call_srcu);
 183
 184/*
 185 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 186 */
 187void synchronize_srcu(struct srcu_struct *sp)
 188{
 189        struct rcu_synchronize rs;
 190
 191        init_rcu_head_on_stack(&rs.head);
 192        init_completion(&rs.completion);
 193        call_srcu(sp, &rs.head, wakeme_after_rcu);
 194        wait_for_completion(&rs.completion);
 195        destroy_rcu_head_on_stack(&rs.head);
 196}
 197EXPORT_SYMBOL_GPL(synchronize_srcu);
 198
 199/* Lockdep diagnostics.  */
 200void __init rcu_scheduler_starting(void)
 201{
 202        rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
 203}
 204