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, bool quiesced)
  90 {
  91         WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
  92         if (quiesced)
  93                 WARN_ON(work_pending(&sp->srcu_work));
  94         else
  95                 flush_work(&sp->srcu_work);
  96         WARN_ON(sp->srcu_gp_running);
  97         WARN_ON(sp->srcu_gp_waiting);
  98         WARN_ON(sp->srcu_cb_head);
  99         WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
 100 }
 101 EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
 102
 103 /*
 104  * Removes the count for the old reader from the appropriate element of
 105  * the srcu_struct.
 106  */
 107 void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 108 {
 109         int newval = sp->srcu_lock_nesting[idx] - 1;
 110
 111         WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
 112         if (!newval && READ_ONCE(sp->srcu_gp_waiting))
 113                 swake_up(&sp->srcu_wq);
 114 }
 115 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 116
 117 /*
 118  * Workqueue handler to drive one grace period and invoke any callbacks
 119  * that become ready as a result.  Single-CPU and !PREEMPT operation
 120  * means that we get away with murder on synchronization.  ;-)
 121  */
 122 void srcu_drive_gp(struct work_struct *wp)
 123 {
 124         int idx;
 125         struct rcu_head *lh;
 126         struct rcu_head *rhp;
 127         struct srcu_struct *sp;
 128
 129         sp = container_of(wp, struct srcu_struct, srcu_work);
 130         if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head))
 131                 return; /* Already running or nothing to do. */
 132
 133         /* Remove recently arrived callbacks and wait for readers. */
 134         WRITE_ONCE(sp->srcu_gp_running, true);
 135         local_irq_disable();
 136         lh = sp->srcu_cb_head;
 137         sp->srcu_cb_head = NULL;
 138         sp->srcu_cb_tail = &sp->srcu_cb_head;
 139         local_irq_enable();
 140         idx = sp->srcu_idx;
 141         WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
 142         WRITE_ONCE(sp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 143         swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
 144         WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
 145
 146         /* Invoke the callbacks we removed above. */
 147         while (lh) {
 148                 rhp = lh;
 149                 lh = lh->next;
 150                 local_bh_disable();
 151                 rhp->func(rhp);
 152                 local_bh_enable();
 153         }
 154
 155         /*
 156          * Enable rescheduling, and if there are more callbacks,
 157          * reschedule ourselves.  This can race with a call_srcu()
 158          * at interrupt level, but the ->srcu_gp_running checks will
 159          * straighten that out.
 160          */
 161         WRITE_ONCE(sp->srcu_gp_running, false);
 162         if (READ_ONCE(sp->srcu_cb_head))
 163                 schedule_work(&sp->srcu_work);
 164 }
 165 EXPORT_SYMBOL_GPL(srcu_drive_gp);
 166
 167 /*
 168  * Enqueue an SRCU callback on the specified srcu_struct structure,
 169  * initiating grace-period processing if it is not already running.
 170  */
 171 void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
 172                rcu_callback_t func)
 173 {
 174         unsigned long flags;
 175
 176         rhp->func = func;
 177         rhp->next = NULL;
 178         local_irq_save(flags);
 179         *sp->srcu_cb_tail = rhp;
 180         sp->srcu_cb_tail = &rhp->next;
 181         local_irq_restore(flags);
 182         if (!READ_ONCE(sp->srcu_gp_running))
 183                 schedule_work(&sp->srcu_work);
 184 }
 185 EXPORT_SYMBOL_GPL(call_srcu);
 186
 187 /*
 188  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 189  */
 190 void synchronize_srcu(struct srcu_struct *sp)
 191 {
 192         struct rcu_synchronize rs;
 193
 194         init_rcu_head_on_stack(&rs.head);
 195         init_completion(&rs.completion);
 196         call_srcu(sp, &rs.head, wakeme_after_rcu);
 197         wait_for_completion(&rs.completion);
 198         destroy_rcu_head_on_stack(&rs.head);
 199 }
 200 EXPORT_SYMBOL_GPL(synchronize_srcu);
 201
 202 /* Lockdep diagnostics.  */
 203 void __init rcu_scheduler_starting(void)
 204 {
 205         rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
 206 }