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