kernel/rcu/srcutiny.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * Sleepable Read-Copy Update mechanism for mutual exclusion,
   4  *      tiny version for non-preemptible single-CPU use.
   5  *
   6  * Copyright (C) IBM Corporation, 2017
   7  *
   8  * Author: Paul McKenney <paulmck@linux.ibm.com>
   9  */
  10
  11 #include <linux/export.h>
  12 #include <linux/mutex.h>
  13 #include <linux/preempt.h>
  14 #include <linux/rcupdate_wait.h>
  15 #include <linux/sched.h>
  16 #include <linux/delay.h>
  17 #include <linux/srcu.h>
  18
  19 #include <linux/rcu_node_tree.h>
  20 #include "rcu_segcblist.h"
  21 #include "rcu.h"
  22
  23 int rcu_scheduler_active __read_mostly;
  24 static LIST_HEAD(srcu_boot_list);
  25 static bool srcu_init_done;
  26
  27 static int init_srcu_struct_fields(struct srcu_struct *ssp)
  28 {
  29         ssp->srcu_lock_nesting[0] = 0;
  30         ssp->srcu_lock_nesting[1] = 0;
  31         init_swait_queue_head(&ssp->srcu_wq);
  32         ssp->srcu_cb_head = NULL;
  33         ssp->srcu_cb_tail = &ssp->srcu_cb_head;
  34         ssp->srcu_gp_running = false;
  35         ssp->srcu_gp_waiting = false;
  36         ssp->srcu_idx = 0;
  37         INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
  38         INIT_LIST_HEAD(&ssp->srcu_work.entry);
  39         return 0;
  40 }
  41
  42 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  43
  44 int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
  45                        struct lock_class_key *key)
  46 {
  47         /* Don't re-initialize a lock while it is held. */
  48         debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
  49         lockdep_init_map(&ssp->dep_map, name, key, 0);
  50         return init_srcu_struct_fields(ssp);
  51 }
  52 EXPORT_SYMBOL_GPL(__init_srcu_struct);
  53
  54 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  55
  56 /*
  57  * init_srcu_struct - initialize a sleep-RCU structure
  58  * @ssp: structure to initialize.
  59  *
  60  * Must invoke this on a given srcu_struct before passing that srcu_struct
  61  * to any other function.  Each srcu_struct represents a separate domain
  62  * of SRCU protection.
  63  */
  64 int init_srcu_struct(struct srcu_struct *ssp)
  65 {
  66         return init_srcu_struct_fields(ssp);
  67 }
  68 EXPORT_SYMBOL_GPL(init_srcu_struct);
  69
  70 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  71
  72 /*
  73  * cleanup_srcu_struct - deconstruct a sleep-RCU structure
  74  * @ssp: structure to clean up.
  75  *
  76  * Must invoke this after you are finished using a given srcu_struct that
  77  * was initialized via init_srcu_struct(), else you leak memory.
  78  */
  79 void cleanup_srcu_struct(struct srcu_struct *ssp)
  80 {
  81         WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
  82         flush_work(&ssp->srcu_work);
  83         WARN_ON(ssp->srcu_gp_running);
  84         WARN_ON(ssp->srcu_gp_waiting);
  85         WARN_ON(ssp->srcu_cb_head);
  86         WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
  87 }
  88 EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
  89
  90 /*
  91  * Removes the count for the old reader from the appropriate element of
  92  * the srcu_struct.
  93  */
  94 void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
  95 {
  96         int newval = ssp->srcu_lock_nesting[idx] - 1;
  97
  98         WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
  99         if (!newval && READ_ONCE(ssp->srcu_gp_waiting))
 100                 swake_up_one(&ssp->srcu_wq);
 101 }
 102 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 103
 104 /*
 105  * Workqueue handler to drive one grace period and invoke any callbacks
 106  * that become ready as a result.  Single-CPU and !PREEMPTION operation
 107  * means that we get away with murder on synchronization.  ;-)
 108  */
 109 void srcu_drive_gp(struct work_struct *wp)
 110 {
 111         int idx;
 112         struct rcu_head *lh;
 113         struct rcu_head *rhp;
 114         struct srcu_struct *ssp;
 115
 116         ssp = container_of(wp, struct srcu_struct, srcu_work);
 117         if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head))
 118                 return; /* Already running or nothing to do. */
 119
 120         /* Remove recently arrived callbacks and wait for readers. */
 121         WRITE_ONCE(ssp->srcu_gp_running, true);
 122         local_irq_disable();
 123         lh = ssp->srcu_cb_head;
 124         ssp->srcu_cb_head = NULL;
 125         ssp->srcu_cb_tail = &ssp->srcu_cb_head;
 126         local_irq_enable();
 127         idx = ssp->srcu_idx;
 128         WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx);
 129         WRITE_ONCE(ssp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 130         swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
 131         WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
 132
 133         /* Invoke the callbacks we removed above. */
 134         while (lh) {
 135                 rhp = lh;
 136                 lh = lh->next;
 137                 local_bh_disable();
 138                 rhp->func(rhp);
 139                 local_bh_enable();
 140         }
 141
 142         /*
 143          * Enable rescheduling, and if there are more callbacks,
 144          * reschedule ourselves.  This can race with a call_srcu()
 145          * at interrupt level, but the ->srcu_gp_running checks will
 146          * straighten that out.
 147          */
 148         WRITE_ONCE(ssp->srcu_gp_running, false);
 149         if (READ_ONCE(ssp->srcu_cb_head))
 150                 schedule_work(&ssp->srcu_work);
 151 }
 152 EXPORT_SYMBOL_GPL(srcu_drive_gp);
 153
 154 /*
 155  * Enqueue an SRCU callback on the specified srcu_struct structure,
 156  * initiating grace-period processing if it is not already running.
 157  */
 158 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 159                rcu_callback_t func)
 160 {
 161         unsigned long flags;
 162
 163         rhp->func = func;
 164         rhp->next = NULL;
 165         local_irq_save(flags);
 166         *ssp->srcu_cb_tail = rhp;
 167         ssp->srcu_cb_tail = &rhp->next;
 168         local_irq_restore(flags);
 169         if (!READ_ONCE(ssp->srcu_gp_running)) {
 170                 if (likely(srcu_init_done))
 171                         schedule_work(&ssp->srcu_work);
 172                 else if (list_empty(&ssp->srcu_work.entry))
 173                         list_add(&ssp->srcu_work.entry, &srcu_boot_list);
 174         }
 175 }
 176 EXPORT_SYMBOL_GPL(call_srcu);
 177
 178 /*
 179  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 180  */
 181 void synchronize_srcu(struct srcu_struct *ssp)
 182 {
 183         struct rcu_synchronize rs;
 184
 185         init_rcu_head_on_stack(&rs.head);
 186         init_completion(&rs.completion);
 187         call_srcu(ssp, &rs.head, wakeme_after_rcu);
 188         wait_for_completion(&rs.completion);
 189         destroy_rcu_head_on_stack(&rs.head);
 190 }
 191 EXPORT_SYMBOL_GPL(synchronize_srcu);
 192
 193 /* Lockdep diagnostics.  */
 194 void __init rcu_scheduler_starting(void)
 195 {
 196         rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
 197 }
 198
 199 /*
 200  * Queue work for srcu_struct structures with early boot callbacks.
 201  * The work won't actually execute until the workqueue initialization
 202  * phase that takes place after the scheduler starts.
 203  */
 204 void __init srcu_init(void)
 205 {
 206         struct srcu_struct *ssp;
 207
 208         srcu_init_done = true;
 209         while (!list_empty(&srcu_boot_list)) {
 210                 ssp = list_first_entry(&srcu_boot_list,
 211                                       struct srcu_struct, srcu_work.entry);
 212                 list_del_init(&ssp->srcu_work.entry);
 213                 schedule_work(&ssp->srcu_work);
 214         }
 215 }