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, bool quiesced)
  80 {
  81         WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
  82         if (quiesced)
  83                 WARN_ON(work_pending(&ssp->srcu_work));
  84         else
  85                 flush_work(&ssp->srcu_work);
  86         WARN_ON(ssp->srcu_gp_running);
  87         WARN_ON(ssp->srcu_gp_waiting);
  88         WARN_ON(ssp->srcu_cb_head);
  89         WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
  90 }
  91 EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
  92
  93 /*
  94  * Removes the count for the old reader from the appropriate element of
  95  * the srcu_struct.
  96  */
  97 void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
  98 {
  99         int newval = ssp->srcu_lock_nesting[idx] - 1;
 100
 101         WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
 102         if (!newval && READ_ONCE(ssp->srcu_gp_waiting))
 103                 swake_up_one(&ssp->srcu_wq);
 104 }
 105 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 106
 107 /*
 108  * Workqueue handler to drive one grace period and invoke any callbacks
 109  * that become ready as a result.  Single-CPU and !PREEMPT operation
 110  * means that we get away with murder on synchronization.  ;-)
 111  */
 112 void srcu_drive_gp(struct work_struct *wp)
 113 {
 114         int idx;
 115         struct rcu_head *lh;
 116         struct rcu_head *rhp;
 117         struct srcu_struct *ssp;
 118
 119         ssp = container_of(wp, struct srcu_struct, srcu_work);
 120         if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head))
 121                 return; /* Already running or nothing to do. */
 122
 123         /* Remove recently arrived callbacks and wait for readers. */
 124         WRITE_ONCE(ssp->srcu_gp_running, true);
 125         local_irq_disable();
 126         lh = ssp->srcu_cb_head;
 127         ssp->srcu_cb_head = NULL;
 128         ssp->srcu_cb_tail = &ssp->srcu_cb_head;
 129         local_irq_enable();
 130         idx = ssp->srcu_idx;
 131         WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx);
 132         WRITE_ONCE(ssp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 133         swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
 134         WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
 135
 136         /* Invoke the callbacks we removed above. */
 137         while (lh) {
 138                 rhp = lh;
 139                 lh = lh->next;
 140                 local_bh_disable();
 141                 rhp->func(rhp);
 142                 local_bh_enable();
 143         }
 144
 145         /*
 146          * Enable rescheduling, and if there are more callbacks,
 147          * reschedule ourselves.  This can race with a call_srcu()
 148          * at interrupt level, but the ->srcu_gp_running checks will
 149          * straighten that out.
 150          */
 151         WRITE_ONCE(ssp->srcu_gp_running, false);
 152         if (READ_ONCE(ssp->srcu_cb_head))
 153                 schedule_work(&ssp->srcu_work);
 154 }
 155 EXPORT_SYMBOL_GPL(srcu_drive_gp);
 156
 157 /*
 158  * Enqueue an SRCU callback on the specified srcu_struct structure,
 159  * initiating grace-period processing if it is not already running.
 160  */
 161 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 162                rcu_callback_t func)
 163 {
 164         unsigned long flags;
 165
 166         rhp->func = func;
 167         rhp->next = NULL;
 168         local_irq_save(flags);
 169         *ssp->srcu_cb_tail = rhp;
 170         ssp->srcu_cb_tail = &rhp->next;
 171         local_irq_restore(flags);
 172         if (!READ_ONCE(ssp->srcu_gp_running)) {
 173                 if (likely(srcu_init_done))
 174                         schedule_work(&ssp->srcu_work);
 175                 else if (list_empty(&ssp->srcu_work.entry))
 176                         list_add(&ssp->srcu_work.entry, &srcu_boot_list);
 177         }
 178 }
 179 EXPORT_SYMBOL_GPL(call_srcu);
 180
 181 /*
 182  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
 183  */
 184 void synchronize_srcu(struct srcu_struct *ssp)
 185 {
 186         struct rcu_synchronize rs;
 187
 188         init_rcu_head_on_stack(&rs.head);
 189         init_completion(&rs.completion);
 190         call_srcu(ssp, &rs.head, wakeme_after_rcu);
 191         wait_for_completion(&rs.completion);
 192         destroy_rcu_head_on_stack(&rs.head);
 193 }
 194 EXPORT_SYMBOL_GPL(synchronize_srcu);
 195
 196 /* Lockdep diagnostics.  */
 197 void __init rcu_scheduler_starting(void)
 198 {
 199         rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
 200 }
 201
 202 /*
 203  * Queue work for srcu_struct structures with early boot callbacks.
 204  * The work won't actually execute until the workqueue initialization
 205  * phase that takes place after the scheduler starts.
 206  */
 207 void __init srcu_init(void)
 208 {
 209         struct srcu_struct *ssp;
 210
 211         srcu_init_done = true;
 212         while (!list_empty(&srcu_boot_list)) {
 213                 ssp = list_first_entry(&srcu_boot_list,
 214                                       struct srcu_struct, srcu_work.entry);
 215                 list_del_init(&ssp->srcu_work.entry);
 216                 schedule_work(&ssp->srcu_work);
 217         }
 218 }