Commit dad81a20 authored by Paul E. McKenney's avatar Paul E. McKenney

srcu: Introduce CLASSIC_SRCU Kconfig option

The TREE_SRCU rewrite is large and a bit on the non-simple side, so
this commit helps reduce risk by allowing the old v4.11 SRCU algorithm
to be selected using a new CLASSIC_SRCU Kconfig option that depends
on RCU_EXPERT.  The default is to use the new TREE_SRCU and TINY_SRCU
algorithms, in order to help get these the testing that they need.
However, if your users do not require the update-side scalability that
is to be provided by TREE_SRCU, select RCU_EXPERT and then CLASSIC_SRCU
to revert back to the old classic SRCU algorithm.
Signed-off-by: default avatarPaul E. McKenney <>
parent 32071141
......@@ -60,6 +60,8 @@ int init_srcu_struct(struct srcu_struct *sp);
#include <linux/srcutiny.h>
#elif defined(CONFIG_TREE_SRCU)
#include <linux/srcutree.h>
#elif defined(CONFIG_CLASSIC_SRCU)
#include <linux/srcuclassic.h>
#error "Unknown SRCU implementation specified to kernel configuration"
* Sleepable Read-Copy Update mechanism for mutual exclusion,
* classic v4.11 variant.
* 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 2 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
* 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, you can access it online at
* Copyright (C) IBM Corporation, 2017
* Author: Paul McKenney <>
struct srcu_array {
unsigned long lock_count[2];
unsigned long unlock_count[2];
struct rcu_batch {
struct rcu_head *head, **tail;
#define RCU_BATCH_INIT(name) { NULL, &(name.head) }
struct srcu_struct {
unsigned long completed;
struct srcu_array __percpu *per_cpu_ref;
spinlock_t queue_lock; /* protect ->batch_queue, ->running */
bool running;
/* callbacks just queued */
struct rcu_batch batch_queue;
/* callbacks try to do the first check_zero */
struct rcu_batch batch_check0;
/* callbacks done with the first check_zero and the flip */
struct rcu_batch batch_check1;
struct rcu_batch batch_done;
struct delayed_work work;
struct lockdep_map dep_map;
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
void process_srcu(struct work_struct *work);
#define __SRCU_STRUCT_INIT(name) \
{ \
.completed = -300, \
.per_cpu_ref = &name##_srcu_array, \
.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \
.running = false, \
.batch_queue = RCU_BATCH_INIT(name.batch_queue), \
.batch_check0 = RCU_BATCH_INIT(name.batch_check0), \
.batch_check1 = RCU_BATCH_INIT(name.batch_check1), \
.batch_done = RCU_BATCH_INIT(name.batch_done), \
.work = __DELAYED_WORK_INITIALIZER(, process_srcu, 0),\
* Define and initialize a srcu struct at build time.
* Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
* Note that although DEFINE_STATIC_SRCU() hides the name from other
* files, the per-CPU variable rules nevertheless require that the
* chosen name be globally unique. These rules also prohibit use of
* DEFINE_STATIC_SRCU() within a function. If these rules are too
* restrictive, declare the srcu_struct manually. For example, in
* each file:
* static struct srcu_struct my_srcu;
* Then, before the first use of each my_srcu, manually initialize it:
* init_srcu_struct(&my_srcu);
* See include/linux/percpu-defs.h for the rules on per-CPU variables.
#define __DEFINE_SRCU(name, is_static) \
static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\
is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
#define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */)
#define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static)
void synchronize_srcu_expedited(struct srcu_struct *sp);
void srcu_barrier(struct srcu_struct *sp);
unsigned long srcu_batches_completed(struct srcu_struct *sp);
......@@ -526,15 +526,32 @@ config SRCU
permits arbitrary sleeping or blocking within RCU read-side critical
bool "Use v4.11 classic SRCU implementation"
default n
depends on RCU_EXPERT && SRCU
This option selects the traditional well-tested classic SRCU
implementation from v4.11, as might be desired for enterprise
Linux distributions. Without this option, the shiny new
Tiny SRCU and Tree SRCU implementations are used instead.
At some point, it is hoped that Tiny SRCU and Tree SRCU
will accumulate enough test time and confidence to allow
Classic SRCU to be dropped entirely.
Say Y if you need a rock-solid SRCU.
Say N if you would like help test Tree SRCU.
config TINY_SRCU
default y if TINY_RCU
default y if TINY_RCU && !CLASSIC_SRCU
This option selects the single-CPU non-preemptible version of SRCU.
config TREE_SRCU
default y if !TINY_RCU
default y if !TINY_RCU && !CLASSIC_SRCU
This option selects the full-fledged version of SRCU.
......@@ -3,7 +3,8 @@
obj-y += update.o sync.o
obj-$(CONFIG_TREE_SRCU) += srcu.o
obj-$(CONFIG_CLASSIC_SRCU) += srcu.o
obj-$(CONFIG_TREE_SRCU) += srcutree.o
obj-$(CONFIG_TINY_SRCU) += srcutiny.o
obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
......@@ -562,7 +562,7 @@ static void srcu_torture_stats(void)
int __maybe_unused cpu;
int idx;
idx = srcu_ctlp->completed & 0x1;
pr_alert("%s%s Tree SRCU per-CPU(idx=%d):",
torture_type, TORTURE_FLAG, idx);
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