// SPDX-License-Identifier: GPL-2.0+
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/*
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* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
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*
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* Copyright IBM Corporation, 2008
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*
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* Author: Paul E. McKenney <paulmck@linux.ibm.com>
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU
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*/
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#include <linux/completion.h>
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#include <linux/interrupt.h>
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#include <linux/notifier.h>
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#include <linux/rcupdate_wait.h>
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/mutex.h>
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#include <linux/sched.h>
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#include <linux/types.h>
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#include <linux/init.h>
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#include <linux/time.h>
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#include <linux/cpu.h>
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#include <linux/prefetch.h>
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#include <linux/slab.h>
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#include <linux/mm.h>
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#include "rcu.h"
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/* Global control variables for rcupdate callback mechanism. */
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struct rcu_ctrlblk {
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struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
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struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
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struct rcu_head **curtail; /* ->next pointer of last CB. */
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};
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/* Definition for rcupdate control block. */
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static struct rcu_ctrlblk rcu_ctrlblk = {
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.donetail = &rcu_ctrlblk.rcucblist,
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.curtail = &rcu_ctrlblk.rcucblist,
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};
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void rcu_barrier(void)
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{
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wait_rcu_gp(call_rcu);
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}
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EXPORT_SYMBOL(rcu_barrier);
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/* Record an rcu quiescent state. */
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void rcu_qs(void)
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{
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unsigned long flags;
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local_irq_save(flags);
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if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
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rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
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raise_softirq_irqoff(RCU_SOFTIRQ);
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}
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local_irq_restore(flags);
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}
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/*
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* Check to see if the scheduling-clock interrupt came from an extended
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* quiescent state, and, if so, tell RCU about it. This function must
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* be called from hardirq context. It is normally called from the
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* scheduling-clock interrupt.
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*/
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void rcu_sched_clock_irq(int user)
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{
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if (user) {
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rcu_qs();
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} else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
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set_tsk_need_resched(current);
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set_preempt_need_resched();
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}
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}
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/*
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* Reclaim the specified callback, either by invoking it for non-kfree cases or
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* freeing it directly (for kfree). Return true if kfreeing, false otherwise.
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*/
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static inline bool rcu_reclaim_tiny(struct rcu_head *head)
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{
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rcu_callback_t f;
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unsigned long offset = (unsigned long)head->func;
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rcu_lock_acquire(&rcu_callback_map);
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if (__is_kvfree_rcu_offset(offset)) {
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trace_rcu_invoke_kvfree_callback("", head, offset);
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kvfree((void *)head - offset);
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rcu_lock_release(&rcu_callback_map);
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return true;
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}
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trace_rcu_invoke_callback("", head);
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f = head->func;
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WRITE_ONCE(head->func, (rcu_callback_t)0L);
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f(head);
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rcu_lock_release(&rcu_callback_map);
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return false;
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}
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/* Invoke the RCU callbacks whose grace period has elapsed. */
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static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
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{
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struct rcu_head *next, *list;
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unsigned long flags;
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/* Move the ready-to-invoke callbacks to a local list. */
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local_irq_save(flags);
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if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
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/* No callbacks ready, so just leave. */
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local_irq_restore(flags);
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return;
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}
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list = rcu_ctrlblk.rcucblist;
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rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
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*rcu_ctrlblk.donetail = NULL;
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if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
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rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
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rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
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local_irq_restore(flags);
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/* Invoke the callbacks on the local list. */
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while (list) {
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next = list->next;
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prefetch(next);
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debug_rcu_head_unqueue(list);
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local_bh_disable();
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rcu_reclaim_tiny(list);
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local_bh_enable();
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list = next;
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}
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}
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/*
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* Wait for a grace period to elapse. But it is illegal to invoke
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* synchronize_rcu() from within an RCU read-side critical section.
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* Therefore, any legal call to synchronize_rcu() is a quiescent
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* state, and so on a UP system, synchronize_rcu() need do nothing.
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* (But Lai Jiangshan points out the benefits of doing might_sleep()
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* to reduce latency.)
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*
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* Cool, huh? (Due to Josh Triplett.)
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*/
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void synchronize_rcu(void)
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{
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RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
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lock_is_held(&rcu_lock_map) ||
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lock_is_held(&rcu_sched_lock_map),
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"Illegal synchronize_rcu() in RCU read-side critical section");
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}
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EXPORT_SYMBOL_GPL(synchronize_rcu);
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/*
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* Post an RCU callback to be invoked after the end of an RCU grace
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* period. But since we have but one CPU, that would be after any
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* quiescent state.
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*/
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void call_rcu(struct rcu_head *head, rcu_callback_t func)
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{
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unsigned long flags;
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debug_rcu_head_queue(head);
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head->func = func;
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head->next = NULL;
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local_irq_save(flags);
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*rcu_ctrlblk.curtail = head;
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rcu_ctrlblk.curtail = &head->next;
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local_irq_restore(flags);
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if (unlikely(is_idle_task(current))) {
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/* force scheduling for rcu_qs() */
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resched_cpu(0);
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}
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}
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EXPORT_SYMBOL_GPL(call_rcu);
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void __init rcu_init(void)
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{
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open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
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rcu_early_boot_tests();
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srcu_init();
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}
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