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.h"
  34
  35 static int init_srcu_struct_fields(struct srcu_struct *sp)
  36 {
  37         sp->srcu_lock_nesting[0] = 0;
  38         sp->srcu_lock_nesting[1] = 0;
  39         init_swait_queue_head(&sp->srcu_wq);
  40         sp->srcu_gp_seq = 0;
  41         rcu_segcblist_init(&sp->srcu_cblist);
  42         sp->srcu_gp_running = false;
  43         sp->srcu_gp_waiting = false;
  44         sp->srcu_idx = 0;
  45         INIT_WORK(&sp->srcu_work, srcu_drive_gp);
  46         return 0;
  47 }
  48
  49 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  50
  51 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
  52                        struct lock_class_key *key)
  53 {
  54         /* Don't re-initialize a lock while it is held. */
  55         debug_check_no_locks_freed((void *)sp, sizeof(*sp));
  56         lockdep_init_map(&sp->dep_map, name, key, 0);
  57         return init_srcu_struct_fields(sp);
  58 }
  59 EXPORT_SYMBOL_GPL(__init_srcu_struct);
  60
  61 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  62
  63 /*
  64  * init_srcu_struct - initialize a sleep-RCU structure
  65  * @sp: structure to initialize.
  66  *
  67  * Must invoke this on a given srcu_struct before passing that srcu_struct
  68  * to any other function.  Each srcu_struct represents a separate domain
  69  * of SRCU protection.
  70  */
  71 int init_srcu_struct(struct srcu_struct *sp)
  72 {
  73         return init_srcu_struct_fields(sp);
  74 }
  75 EXPORT_SYMBOL_GPL(init_srcu_struct);
  76
  77 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  78
  79 /*
  80  * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  81  * @sp: structure to clean up.
  82  *
  83  * Must invoke this after you are finished using a given srcu_struct that
  84  * was initialized via init_srcu_struct(), else you leak memory.
  85  */
  86 void cleanup_srcu_struct(struct srcu_struct *sp)
  87 {
  88         WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
  89         flush_work(&sp->srcu_work);
  90         WARN_ON(rcu_seq_state(sp->srcu_gp_seq));
  91         WARN_ON(sp->srcu_gp_running);
  92         WARN_ON(sp->srcu_gp_waiting);
  93         WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist));
  94 }
  95 EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
  96
  97 /*
  98  * Counts the new reader in the appropriate per-CPU element of the
  99  * srcu_struct.  Must be called from process context.
 100  * Returns an index that must be passed to the matching srcu_read_unlock().
 101  */
 102 int __srcu_read_lock(struct srcu_struct *sp)
 103 {
 104         int idx;
 105
 106         idx = READ_ONCE(sp->srcu_idx);
 107         WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1);
 108         return idx;
 109 }
 110 EXPORT_SYMBOL_GPL(__srcu_read_lock);
 111
 112 /*
 113  * Removes the count for the old reader from the appropriate element of
 114  * the srcu_struct.  Must be called from process context.
 115  */
 116 void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 117 {
 118         int newval = sp->srcu_lock_nesting[idx] - 1;
 119
 120         WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
 121         if (!newval && READ_ONCE(sp->srcu_gp_waiting))
 122                 swake_up(&sp->srcu_wq);
 123 }
 124 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 125
 126 /*
 127  * Workqueue handler to drive one grace period and invoke any callbacks
 128  * that become ready as a result.  Single-CPU and !PREEMPT operation
 129  * means that we get away with murder on synchronization.  ;-)
 130  */
 131 void srcu_drive_gp(struct work_struct *wp)
 132 {
 133         int idx;
 134         struct rcu_cblist ready_cbs;
 135         struct srcu_struct *sp;
 136         struct rcu_head *rhp;
 137
 138         sp = container_of(wp, struct srcu_struct, srcu_work);
 139         if (sp->srcu_gp_running || rcu_segcblist_empty(&sp->srcu_cblist))
 140                 return; /* Already running or nothing to do. */
 141
 142         /* Tag recently arrived callbacks and wait for readers. */
 143         WRITE_ONCE(sp->srcu_gp_running, true);
 144         rcu_segcblist_accelerate(&sp->srcu_cblist,
 145                                  rcu_seq_snap(&sp->srcu_gp_seq));
 146         rcu_seq_start(&sp->srcu_gp_seq);
 147         idx = sp->srcu_idx;
 148         WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
 149         WRITE_ONCE(sp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 150         swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
 151         WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
 152         rcu_seq_end(&sp->srcu_gp_seq);
 153
 154         /* Update callback list based on GP, and invoke ready callbacks. */
 155         rcu_segcblist_advance(&sp->srcu_cblist,
 156                               rcu_seq_current(&sp->srcu_gp_seq));
 157         if (rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
 158                 rcu_cblist_init(&ready_cbs);
 159                 local_irq_disable();
 160                 rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
 161                 local_irq_enable();
 162                 rhp = rcu_cblist_dequeue(&ready_cbs);
 163                 for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
 164                         local_bh_disable();
 165                         rhp->func(rhp);
 166                         local_bh_enable();
 167                 }
 168                 local_irq_disable();
 169                 rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
 170                 local_irq_enable();
 171         }
 172         WRITE_ONCE(sp->srcu_gp_running, false);
 173
 174         /*
 175          * If more callbacks, reschedule ourselves.  This can race with
 176          * a call_srcu() at interrupt level, but the ->srcu_gp_running
 177          * checks will straighten that out.
 178          */
 179         if (!rcu_segcblist_empty(&sp->srcu_cblist))
 180                 schedule_work(&sp->srcu_work);
 181 }
 182 EXPORT_SYMBOL_GPL(srcu_drive_gp);
 183
 184 /*
 185  * Enqueue an SRCU callback on the specified srcu_struct structure,
 186  * initiating grace-period processing if it is not already running.
 187  */
 188 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 189                rcu_callback_t func)
 190 {
 191         unsigned long flags;
 192
 193         head->func = func;
 194         local_irq_save(flags);
 195         rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
 196         local_irq_restore(flags);
 197         if (!READ_ONCE(sp->srcu_gp_running))
 198                 schedule_work(&sp->srcu_work);
 199 }
 200 EXPORT_SYMBOL_GPL(call_srcu);
 201
 202 /*
 203  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 204  */
 205 void synchronize_srcu(struct srcu_struct *sp)
 206 {
 207         struct rcu_synchronize rs;
 208
 209         init_rcu_head_on_stack(&rs.head);
 210         init_completion(&rs.completion);
 211         call_srcu(sp, &rs.head, wakeme_after_rcu);
 212         wait_for_completion(&rs.completion);
 213         destroy_rcu_head_on_stack(&rs.head);
 214 }
 215 EXPORT_SYMBOL_GPL(synchronize_srcu);