2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright (C) IBM Corporation, 2001
20 * Author: Dipankar Sarma <dipankar@in.ibm.com>
22 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
23 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 * For detailed explanation of Read-Copy Update mechanism see -
29 * http://lse.sourceforge.net/locking/rcupdate.html
33 #ifndef __LINUX_RCUPDATE_H
34 #define __LINUX_RCUPDATE_H
38 #include <linux/config.h>
39 #include <linux/cache.h>
40 #include <linux/spinlock.h>
41 #include <linux/threads.h>
44 #error "SMP configurations not supported for RCU backport."
48 * struct rcu_head - callback structure for use with RCU
49 * @next: next update requests in a list
50 * @func: actual update function to call after the grace period.
53 struct rcu_head *next;
54 void (*func)(struct rcu_head *head);
57 #define RCU_HEAD_INIT { }
58 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
59 #define INIT_RCU_HEAD(ptr) do { } while (0)
64 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
66 * When synchronize_rcu() is invoked on one CPU while other CPUs
67 * are within RCU read-side critical sections, then the
68 * synchronize_rcu() is guaranteed to block until after all the other
69 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
70 * on one CPU while other CPUs are within RCU read-side critical
71 * sections, invocation of the corresponding RCU callback is deferred
72 * until after the all the other CPUs exit their critical sections.
74 * Note, however, that RCU callbacks are permitted to run concurrently
75 * with RCU read-side critical sections. One way that this can happen
76 * is via the following sequence of events: (1) CPU 0 enters an RCU
77 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
78 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
79 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
80 * callback is invoked. This is legal, because the RCU read-side critical
81 * section that was running concurrently with the call_rcu() (and which
82 * therefore might be referencing something that the corresponding RCU
83 * callback would free up) has completed before the corresponding
84 * RCU callback is invoked.
86 * RCU read-side critical sections may be nested. Any deferred actions
87 * will be deferred until the outermost RCU read-side critical section
90 * It is illegal to block while in an RCU read-side critical section.
92 #define rcu_read_lock() \
96 * rcu_read_unlock - marks the end of an RCU read-side critical section.
98 * See rcu_read_lock() for more information.
100 #define rcu_read_unlock() \
104 * So where is rcu_write_lock()? It does not exist, as there is no
105 * way for writers to lock out RCU readers. This is a feature, not
106 * a bug -- this property is what provides RCU's performance benefits.
107 * Of course, writers must coordinate with each other. The normal
108 * spinlock primitives work well for this, but any other technique may be
109 * used as well. RCU does not care how the writers keep out of each
110 * others' way, as long as they do so.
114 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
116 * This is equivalent of rcu_read_lock(), but to be used when updates
117 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
118 * consider completion of a softirq handler to be a quiescent state,
119 * a process in RCU read-side critical section must be protected by
120 * disabling softirqs. Read-side critical sections in interrupt context
121 * can use just rcu_read_lock().
124 #define rcu_read_lock_bh() \
126 local_bh_disable(); \
130 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
132 * See rcu_read_lock_bh() for more information.
134 #define rcu_read_unlock_bh() \
140 * rcu_dereference - fetch an RCU-protected pointer in an
141 * RCU read-side critical section. This pointer may later
142 * be safely dereferenced.
144 * Inserts memory barriers on architectures that require them
145 * (currently only the Alpha), and, more importantly, documents
146 * exactly which pointers are protected by RCU.
149 #define rcu_dereference(p) ({ \
150 typeof(p) _________p1 = p; \
151 smp_read_barrier_depends(); \
156 * rcu_assign_pointer - assign (publicize) a pointer to a newly
157 * initialized structure that will be dereferenced by RCU read-side
158 * critical sections. Returns the value assigned.
160 * Inserts memory barriers on architectures that require them
161 * (pretty much all of them other than x86), and also prevents
162 * the compiler from reordering the code that initializes the
163 * structure after the pointer assignment. More importantly, this
164 * call documents which pointers will be dereferenced by RCU read-side
168 #define rcu_assign_pointer(p, v) ({ \
174 * synchronize_sched - block until all CPUs have exited any non-preemptive
175 * kernel code sequences.
177 * This means that all preempt_disable code sequences, including NMI and
178 * hardware-interrupt handlers, in progress on entry will have completed
179 * before this primitive returns. However, this does not guarantee that
180 * softirq handlers will have completed, since in some kernels, these
181 * handlers can run in process context, and can block.
183 * This primitive provides the guarantees made by the (now removed)
184 * synchronize_kernel() API. In contrast, synchronize_rcu() only
185 * guarantees that rcu_read_lock() sections will have completed.
186 * In "classic RCU", these two guarantees happen to be one and
187 * the same, but can differ in realtime RCU implementations.
189 #define synchronize_sched() synchronize_rcu()
191 /* Exported interfaces */
192 void synchronize_rcu(void);
193 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *head));
195 static inline void call_rcu_bh(struct rcu_head *head,
196 void (*func)(struct rcu_head *head))
201 void synchronize_idle(void);
202 extern void rcu_barrier(void);
204 #endif /* __KERNEL__ */
205 #endif /* __LINUX_RCUPDATE_H */