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
  36 int rcu_scheduler_active __read_mostly;
  37
  38 static 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
  54 int __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 }
  62 EXPORT_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  */
  74 int init_srcu_struct(struct srcu_struct *sp)
  75 {
  76         return init_srcu_struct_fields(sp);
  77 }
  78 EXPORT_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  */
  89 void 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 }
  98 EXPORT_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  */
 104 void __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 }
 112 EXPORT_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  */
 119 void 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 }
 162 EXPORT_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  */
 168 void 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 }
 182 EXPORT_SYMBOL_GPL(call_srcu);
 183
 184 /*
 185  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 186  */
 187 void 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 }
 197 EXPORT_SYMBOL_GPL(synchronize_srcu);
 198
 199 /* Lockdep diagnostics.  */
 200 void __init rcu_scheduler_starting(void)
 201 {
 202         rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
 203 }