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