kernel/rcu/tiny.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
   4  *
   5  * Copyright IBM Corporation, 2008
   6  *
   7  * Author: Paul E. McKenney <paulmck@linux.ibm.com>
   8  *
   9  * For detailed explanation of Read-Copy Update mechanism see -
  10  *              Documentation/RCU
  11  */
  12 #include <linux/completion.h>
  13 #include <linux/interrupt.h>
  14 #include <linux/notifier.h>
  15 #include <linux/rcupdate_wait.h>
  16 #include <linux/kernel.h>
  17 #include <linux/export.h>
  18 #include <linux/mutex.h>
  19 #include <linux/sched.h>
  20 #include <linux/types.h>
  21 #include <linux/init.h>
  22 #include <linux/time.h>
  23 #include <linux/cpu.h>
  24 #include <linux/prefetch.h>
  25 #include <linux/slab.h>
  26 #include <linux/mm.h>
  27
  28 #include "rcu.h"
  29
  30 /* Global control variables for rcupdate callback mechanism. */
  31 struct rcu_ctrlblk {
  32         struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
  33         struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
  34         struct rcu_head **curtail;      /* ->next pointer of last CB. */
  35         unsigned long gp_seq;           /* Grace-period counter. */
  36 };
  37
  38 /* Definition for rcupdate control block. */
  39 static struct rcu_ctrlblk rcu_ctrlblk = {
  40         .donetail       = &rcu_ctrlblk.rcucblist,
  41         .curtail        = &rcu_ctrlblk.rcucblist,
  42         .gp_seq         = 0 - 300UL,
  43 };
  44
  45 void rcu_barrier(void)
  46 {
  47         wait_rcu_gp(call_rcu);
  48 }
  49 EXPORT_SYMBOL(rcu_barrier);
  50
  51 /* Record an rcu quiescent state.  */
  52 void rcu_qs(void)
  53 {
  54         unsigned long flags;
  55
  56         local_irq_save(flags);
  57         if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
  58                 rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
  59                 raise_softirq_irqoff(RCU_SOFTIRQ);
  60         }
  61         WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 1);
  62         local_irq_restore(flags);
  63 }
  64
  65 /*
  66  * Check to see if the scheduling-clock interrupt came from an extended
  67  * quiescent state, and, if so, tell RCU about it.  This function must
  68  * be called from hardirq context.  It is normally called from the
  69  * scheduling-clock interrupt.
  70  */
  71 void rcu_sched_clock_irq(int user)
  72 {
  73         if (user) {
  74                 rcu_qs();
  75         } else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
  76                 set_tsk_need_resched(current);
  77                 set_preempt_need_resched();
  78         }
  79 }
  80
  81 /*
  82  * Reclaim the specified callback, either by invoking it for non-kfree cases or
  83  * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
  84  */
  85 static inline bool rcu_reclaim_tiny(struct rcu_head *head)
  86 {
  87         rcu_callback_t f;
  88         unsigned long offset = (unsigned long)head->func;
  89
  90         rcu_lock_acquire(&rcu_callback_map);
  91         if (__is_kvfree_rcu_offset(offset)) {
  92                 trace_rcu_invoke_kvfree_callback("", head, offset);
  93                 kvfree((void *)head - offset);
  94                 rcu_lock_release(&rcu_callback_map);
  95                 return true;
  96         }
  97
  98         trace_rcu_invoke_callback("", head);
  99         f = head->func;
 100         WRITE_ONCE(head->func, (rcu_callback_t)0L);
 101         f(head);
 102         rcu_lock_release(&rcu_callback_map);
 103         return false;
 104 }
 105
 106 /* Invoke the RCU callbacks whose grace period has elapsed.  */
 107 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
 108 {
 109         struct rcu_head *next, *list;
 110         unsigned long flags;
 111
 112         /* Move the ready-to-invoke callbacks to a local list. */
 113         local_irq_save(flags);
 114         if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
 115                 /* No callbacks ready, so just leave. */
 116                 local_irq_restore(flags);
 117                 return;
 118         }
 119         list = rcu_ctrlblk.rcucblist;
 120         rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
 121         *rcu_ctrlblk.donetail = NULL;
 122         if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
 123                 rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
 124         rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
 125         local_irq_restore(flags);
 126
 127         /* Invoke the callbacks on the local list. */
 128         while (list) {
 129                 next = list->next;
 130                 prefetch(next);
 131                 debug_rcu_head_unqueue(list);
 132                 local_bh_disable();
 133                 rcu_reclaim_tiny(list);
 134                 local_bh_enable();
 135                 list = next;
 136         }
 137 }
 138
 139 /*
 140  * Wait for a grace period to elapse.  But it is illegal to invoke
 141  * synchronize_rcu() from within an RCU read-side critical section.
 142  * Therefore, any legal call to synchronize_rcu() is a quiescent
 143  * state, and so on a UP system, synchronize_rcu() need do nothing.
 144  * (But Lai Jiangshan points out the benefits of doing might_sleep()
 145  * to reduce latency.)
 146  *
 147  * Cool, huh?  (Due to Josh Triplett.)
 148  */
 149 void synchronize_rcu(void)
 150 {
 151         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
 152                          lock_is_held(&rcu_lock_map) ||
 153                          lock_is_held(&rcu_sched_lock_map),
 154                          "Illegal synchronize_rcu() in RCU read-side critical section");
 155 }
 156 EXPORT_SYMBOL_GPL(synchronize_rcu);
 157
 158 /*
 159  * Post an RCU callback to be invoked after the end of an RCU grace
 160  * period.  But since we have but one CPU, that would be after any
 161  * quiescent state.
 162  */
 163 void call_rcu(struct rcu_head *head, rcu_callback_t func)
 164 {
 165         unsigned long flags;
 166
 167         debug_rcu_head_queue(head);
 168         head->func = func;
 169         head->next = NULL;
 170
 171         local_irq_save(flags);
 172         *rcu_ctrlblk.curtail = head;
 173         rcu_ctrlblk.curtail = &head->next;
 174         local_irq_restore(flags);
 175
 176         if (unlikely(is_idle_task(current))) {
 177                 /* force scheduling for rcu_qs() */
 178                 resched_cpu(0);
 179         }
 180 }
 181 EXPORT_SYMBOL_GPL(call_rcu);
 182
 183 /*
 184  * Return a grace-period-counter "cookie".  For more information,
 185  * see the Tree RCU header comment.
 186  */
 187 unsigned long get_state_synchronize_rcu(void)
 188 {
 189         return READ_ONCE(rcu_ctrlblk.gp_seq);
 190 }
 191 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
 192
 193 /*
 194  * Return a grace-period-counter "cookie" and ensure that a future grace
 195  * period completes.  For more information, see the Tree RCU header comment.
 196  */
 197 unsigned long start_poll_synchronize_rcu(void)
 198 {
 199         unsigned long gp_seq = get_state_synchronize_rcu();
 200
 201         if (unlikely(is_idle_task(current))) {
 202                 /* force scheduling for rcu_qs() */
 203                 resched_cpu(0);
 204         }
 205         return gp_seq;
 206 }
 207 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
 208
 209 /*
 210  * Return true if the grace period corresponding to oldstate has completed
 211  * and false otherwise.  For more information, see the Tree RCU header
 212  * comment.
 213  */
 214 bool poll_state_synchronize_rcu(unsigned long oldstate)
 215 {
 216         return READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate;
 217 }
 218 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
 219
 220 void __init rcu_init(void)
 221 {
 222         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 223         rcu_early_boot_tests();
 224 }