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/*
* Copyright (c) 2018 Richard Braun.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*
* Read-Copy Update.
*
* This module provides a synchronization framework for read-only lockless
* operations, best used on read-mostly data structures.
*
* To learn more about RCU, see "Is Parallel Programming Hard, And, If So,
* What Can You Do About It ?" by Paul E. McKenney.
*
* A thorough discussion of RCU's requirements can be found at [1].
* However, the memory model and terminology used in that document being
* different from C11, the memory barrier guarantees are hereby translated
* into memory ordering guarantees :
*
* 1. Release-acquire ordering is enforced between the end of all
* read-side critical sections starting before a grace period starts
* and the start of all works deferred before the same grace period
* starts.
* 2. Release-acquire ordering is enforced between the start of all
* read-side critical sections ending after a grace period ends
* and all the work deferrals done before the same grace period
* starts.
* 3. Release-acquire ordering is enforced between all the work deferrals
* done before a grace period starts and the start of all works deferred
* before the same grace period starts.
*
* [1] https://www.kernel.org/doc/Documentation/RCU/Design/Requirements/Requirements.html.
*/
#ifndef KERN_RCU_H
#define KERN_RCU_H
#include <kern/atomic.h>
#include <kern/init.h>
#include <kern/rcu_i.h>
#include <kern/rcu_types.h>
#include <kern/thread.h>
#include <kern/work.h>
/*
* Thread-local RCU data.
*/
struct rcu_reader;
/*
* Safely store a pointer.
*
* This macro enforces release ordering on the given pointer.
*/
#define rcu_store_ptr(ptr, value) atomic_store(&(ptr), value, ATOMIC_RELEASE)
/*
* Safely load a pointer.
*
* This macro enforces consume ordering on the given pointer.
*/
#define rcu_load_ptr(ptr) atomic_load(&(ptr), ATOMIC_CONSUME)
/*
* Read-side critical section functions.
*
* Critical sections are preemptible, may safely nest, and may safely
* be used in interrupt context. It is not allowed to sleep inside a
* read-side critical section. However, it is allowed to acquire locks
* that don't sleep, such as spin locks.
*
* Entering or leaving a critical section doesn't provide any memory
* ordering guarantee.
*/
static inline void
rcu_read_enter(void)
{
rcu_reader_inc(thread_rcu_reader(thread_self()));
barrier();
}
static inline void
rcu_read_leave(void)
{
barrier();
rcu_reader_dec(thread_rcu_reader(thread_self()));
}
/*
* Initialize a RCU reader.
*/
void rcu_reader_init(struct rcu_reader *reader);
/*
* Report a context switch on the current processor.
*
* The argument is the RCU reader of the preempted thread.
*
* Interrupts and preemption must be disabled when calling this function.
*/
void rcu_report_context_switch(struct rcu_reader *reader);
/*
* Report a periodic event on the current processor.
*
* Interrupts and preemption must be disabled when calling this function.
*/
void rcu_report_periodic_event(void);
/*
* Defer a work until all existing read-side references are dropped,
* without blocking.
*
* The given work is scheduled when all existing read-side references
* are dropped.
*/
void rcu_defer(struct work *work);
/*
* Wait for all existing read-side references to be dropped.
*
* This function sleeps, and may do so for a moderately long duration,
* at leat a few system timer ticks, sometimes a lot more.
*/
void rcu_wait(void);
/*
* This init operation provides :
* - read-side critical sections usable
*/
INIT_OP_DECLARE(rcu_bootstrap);
#endif /* KERN_RCU_H */
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