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 <paul.mckenney@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/cache.h>
39 #include <linux/spinlock.h>
40 #include <linux/threads.h>
41 #include <linux/percpu.h>
42 #include <linux/cpumask.h>
43 #include <linux/seqlock.h>
46 * struct rcu_head - callback structure for use with RCU
47 * @next: next update requests in a list
48 * @func: actual update function to call after the grace period.
51 struct rcu_head *next;
52 void (*func)(struct rcu_head *head);
55 #define RCU_HEAD_INIT(head) { .next = NULL, .func = NULL }
56 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head)
57 #define INIT_RCU_HEAD(ptr) do { \
58 (ptr)->next = NULL; (ptr)->func = NULL; \
63 /* Global control variables for rcupdate callback mechanism. */
65 long cur; /* Current batch number. */
66 long completed; /* Number of the last completed batch */
67 int next_pending; /* Is the next batch already waiting? */
68 seqcount_t lock; /* For atomic reads of cur and next_pending. */
69 } ____cacheline_maxaligned_in_smp;
71 /* Is batch a before batch b ? */
72 static inline int rcu_batch_before(long a, long b)
77 /* Is batch a after batch b ? */
78 static inline int rcu_batch_after(long a, long b)
84 * Per-CPU data for Read-Copy UPdate.
85 * nxtlist - new callbacks are added here
86 * curlist - current batch for which quiescent cycle started if any
89 /* 1) quiescent state handling : */
90 long quiescbatch; /* Batch # for grace period */
91 long qsctr; /* User-mode/idle loop etc. */
92 long last_qsctr; /* value of qsctr at beginning */
93 /* of rcu grace period */
94 int qs_pending; /* core waits for quiesc state */
96 /* 2) batch handling */
97 long batch; /* Batch # for current RCU batch */
98 struct rcu_head *nxtlist;
99 struct rcu_head **nxttail;
100 struct rcu_head *curlist;
103 DECLARE_PER_CPU(struct rcu_data, rcu_data);
104 extern struct rcu_ctrlblk rcu_ctrlblk;
106 #define RCU_quiescbatch(cpu) (per_cpu(rcu_data, (cpu)).quiescbatch)
107 #define RCU_qsctr(cpu) (per_cpu(rcu_data, (cpu)).qsctr)
108 #define RCU_last_qsctr(cpu) (per_cpu(rcu_data, (cpu)).last_qsctr)
109 #define RCU_qs_pending(cpu) (per_cpu(rcu_data, (cpu)).qs_pending)
110 #define RCU_batch(cpu) (per_cpu(rcu_data, (cpu)).batch)
111 #define RCU_nxtlist(cpu) (per_cpu(rcu_data, (cpu)).nxtlist)
112 #define RCU_curlist(cpu) (per_cpu(rcu_data, (cpu)).curlist)
113 #define RCU_nxttail(cpu) (per_cpu(rcu_data, (cpu)).nxttail)
115 static inline int rcu_pending(int cpu)
117 /* This cpu has pending rcu entries and the grace period
118 * for them has completed.
120 if (RCU_curlist(cpu) &&
121 !rcu_batch_before(rcu_ctrlblk.completed,RCU_batch(cpu)))
124 /* This cpu has no pending entries, but there are new entries */
125 if (!RCU_curlist(cpu) && RCU_nxtlist(cpu))
128 /* The rcu core waits for a quiescent state from the cpu */
129 if (RCU_quiescbatch(cpu) != rcu_ctrlblk.cur || RCU_qs_pending(cpu))
136 #define rcu_read_lock() preempt_disable()
137 #define rcu_read_unlock() preempt_enable()
139 extern void rcu_init(void);
140 extern void rcu_check_callbacks(int cpu, int user);
141 extern void rcu_restart_cpu(int cpu);
143 /* Exported interfaces */
144 extern void FASTCALL(call_rcu(struct rcu_head *head,
145 void (*func)(struct rcu_head *head)));
146 extern void synchronize_kernel(void);
148 #endif /* __KERNEL__ */
149 #endif /* __LINUX_RCUPDATE_H */