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 static LIST_HEAD(srcu_boot_list);
  38 static bool srcu_init_done;
  39
  40 static int init_srcu_struct_fields(struct srcu_struct *sp)
  41 {
  42         sp->srcu_lock_nesting[0] = 0;
  43         sp->srcu_lock_nesting[1] = 0;
  44         init_swait_queue_head(&sp->srcu_wq);
  45         sp->srcu_cb_head = NULL;
  46         sp->srcu_cb_tail = &sp->srcu_cb_head;
  47         sp->srcu_gp_running = false;
  48         sp->srcu_gp_waiting = false;
  49         sp->srcu_idx = 0;
  50         INIT_WORK(&sp->srcu_work, srcu_drive_gp);
  51         INIT_LIST_HEAD(&sp->srcu_work.entry);
  52         return 0;
  53 }
  54
  55 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  56
  57 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
  58                        struct lock_class_key *key)
  59 {
  60         /* Don't re-initialize a lock while it is held. */
  61         debug_check_no_locks_freed((void *)sp, sizeof(*sp));
  62         lockdep_init_map(&sp->dep_map, name, key, 0);
  63         return init_srcu_struct_fields(sp);
  64 }
  65 EXPORT_SYMBOL_GPL(__init_srcu_struct);
  66
  67 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  68
  69 /*
  70  * init_srcu_struct - initialize a sleep-RCU structure
  71  * @sp: structure to initialize.
  72  *
  73  * Must invoke this on a given srcu_struct before passing that srcu_struct
  74  * to any other function.  Each srcu_struct represents a separate domain
  75  * of SRCU protection.
  76  */
  77 int init_srcu_struct(struct srcu_struct *sp)
  78 {
  79         return init_srcu_struct_fields(sp);
  80 }
  81 EXPORT_SYMBOL_GPL(init_srcu_struct);
  82
  83 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  84
  85 /*
  86  * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  87  * @sp: structure to clean up.
  88  *
  89  * Must invoke this after you are finished using a given srcu_struct that
  90  * was initialized via init_srcu_struct(), else you leak memory.
  91  */
  92 void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced)
  93 {
  94         WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
  95         if (quiesced)
  96                 WARN_ON(work_pending(&sp->srcu_work));
  97         else
  98                 flush_work(&sp->srcu_work);
  99         WARN_ON(sp->srcu_gp_running);
 100         WARN_ON(sp->srcu_gp_waiting);
 101         WARN_ON(sp->srcu_cb_head);
 102         WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
 103 }
 104 EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
 105
 106 /*
 107  * Removes the count for the old reader from the appropriate element of
 108  * the srcu_struct.
 109  */
 110 void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 111 {
 112         int newval = sp->srcu_lock_nesting[idx] - 1;
 113
 114         WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
 115         if (!newval && READ_ONCE(sp->srcu_gp_waiting))
 116                 swake_up_one(&sp->srcu_wq);
 117 }
 118 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 119
 120 /*
 121  * Workqueue handler to drive one grace period and invoke any callbacks
 122  * that become ready as a result.  Single-CPU and !PREEMPT operation
 123  * means that we get away with murder on synchronization.  ;-)
 124  */
 125 void srcu_drive_gp(struct work_struct *wp)
 126 {
 127         int idx;
 128         struct rcu_head *lh;
 129         struct rcu_head *rhp;
 130         struct srcu_struct *sp;
 131
 132         sp = container_of(wp, struct srcu_struct, srcu_work);
 133         if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head))
 134                 return; /* Already running or nothing to do. */
 135
 136         /* Remove recently arrived callbacks and wait for readers. */
 137         WRITE_ONCE(sp->srcu_gp_running, true);
 138         local_irq_disable();
 139         lh = sp->srcu_cb_head;
 140         sp->srcu_cb_head = NULL;
 141         sp->srcu_cb_tail = &sp->srcu_cb_head;
 142         local_irq_enable();
 143         idx = sp->srcu_idx;
 144         WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
 145         WRITE_ONCE(sp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 146         swait_event_exclusive(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
 147         WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
 148
 149         /* Invoke the callbacks we removed above. */
 150         while (lh) {
 151                 rhp = lh;
 152                 lh = lh->next;
 153                 local_bh_disable();
 154                 rhp->func(rhp);
 155                 local_bh_enable();
 156         }
 157
 158         /*
 159          * Enable rescheduling, and if there are more callbacks,
 160          * reschedule ourselves.  This can race with a call_srcu()
 161          * at interrupt level, but the ->srcu_gp_running checks will
 162          * straighten that out.
 163          */
 164         WRITE_ONCE(sp->srcu_gp_running, false);
 165         if (READ_ONCE(sp->srcu_cb_head))
 166                 schedule_work(&sp->srcu_work);
 167 }
 168 EXPORT_SYMBOL_GPL(srcu_drive_gp);
 169
 170 /*
 171  * Enqueue an SRCU callback on the specified srcu_struct structure,
 172  * initiating grace-period processing if it is not already running.
 173  */
 174 void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
 175                rcu_callback_t func)
 176 {
 177         unsigned long flags;
 178
 179         rhp->func = func;
 180         rhp->next = NULL;
 181         local_irq_save(flags);
 182         *sp->srcu_cb_tail = rhp;
 183         sp->srcu_cb_tail = &rhp->next;
 184         local_irq_restore(flags);
 185         if (!READ_ONCE(sp->srcu_gp_running)) {
 186                 if (likely(srcu_init_done))
 187                         schedule_work(&sp->srcu_work);
 188                 else if (list_empty(&sp->srcu_work.entry))
 189                         list_add(&sp->srcu_work.entry, &srcu_boot_list);
 190         }
 191 }
 192 EXPORT_SYMBOL_GPL(call_srcu);
 193
 194 /*
 195  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 196  */
 197 void synchronize_srcu(struct srcu_struct *sp)
 198 {
 199         struct rcu_synchronize rs;
 200
 201         init_rcu_head_on_stack(&rs.head);
 202         init_completion(&rs.completion);
 203         call_srcu(sp, &rs.head, wakeme_after_rcu);
 204         wait_for_completion(&rs.completion);
 205         destroy_rcu_head_on_stack(&rs.head);
 206 }
 207 EXPORT_SYMBOL_GPL(synchronize_srcu);
 208
 209 /* Lockdep diagnostics.  */
 210 void __init rcu_scheduler_starting(void)
 211 {
 212         rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
 213 }
 214
 215 /*
 216  * Queue work for srcu_struct structures with early boot callbacks.
 217  * The work won't actually execute until the workqueue initialization
 218  * phase that takes place after the scheduler starts.
 219  */
 220 void __init srcu_init(void)
 221 {
 222         struct srcu_struct *sp;
 223
 224         srcu_init_done = true;
 225         while (!list_empty(&srcu_boot_list)) {
 226                 sp = list_first_entry(&srcu_boot_list,
 227                                       struct srcu_struct, srcu_work.entry);
 228                 list_del_init(&sp->srcu_work.entry);
 229                 schedule_work(&sp->srcu_work);
 230         }
 231 }