Root/kernel/rcu.h

1/*
2 * Read-Copy Update definitions shared among RCU implementations.
3 *
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.
8 *
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.
13 *
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.
17 *
18 * Copyright IBM Corporation, 2011
19 *
20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
21 */
22
23#ifndef __LINUX_RCU_H
24#define __LINUX_RCU_H
25
26#ifdef CONFIG_RCU_TRACE
27#define RCU_TRACE(stmt) stmt
28#else /* #ifdef CONFIG_RCU_TRACE */
29#define RCU_TRACE(stmt)
30#endif /* #else #ifdef CONFIG_RCU_TRACE */
31
32/*
33 * Process-level increment to ->dynticks_nesting field. This allows for
34 * architectures that use half-interrupts and half-exceptions from
35 * process context.
36 *
37 * DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH
38 * that counts the number of process-based reasons why RCU cannot
39 * consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE
40 * is the value used to increment or decrement this field.
41 *
42 * The rest of the bits could in principle be used to count interrupts,
43 * but this would mean that a negative-one value in the interrupt
44 * field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field.
45 * We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK
46 * that is set to DYNTICK_TASK_FLAG upon initial exit from idle.
47 * The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon
48 * initial exit from idle.
49 */
50#define DYNTICK_TASK_NEST_WIDTH 7
51#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1)
52#define DYNTICK_TASK_NEST_MASK (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1)
53#define DYNTICK_TASK_FLAG ((DYNTICK_TASK_NEST_VALUE / 8) * 2)
54#define DYNTICK_TASK_MASK ((DYNTICK_TASK_NEST_VALUE / 8) * 3)
55#define DYNTICK_TASK_EXIT_IDLE (DYNTICK_TASK_NEST_VALUE + \
56                    DYNTICK_TASK_FLAG)
57
58/*
59 * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
60 * by call_rcu() and rcu callback execution, and are therefore not part of the
61 * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
62 */
63
64#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
65# define STATE_RCU_HEAD_READY 0
66# define STATE_RCU_HEAD_QUEUED 1
67
68extern struct debug_obj_descr rcuhead_debug_descr;
69
70static inline void debug_rcu_head_queue(struct rcu_head *head)
71{
72    debug_object_activate(head, &rcuhead_debug_descr);
73    debug_object_active_state(head, &rcuhead_debug_descr,
74                  STATE_RCU_HEAD_READY,
75                  STATE_RCU_HEAD_QUEUED);
76}
77
78static inline void debug_rcu_head_unqueue(struct rcu_head *head)
79{
80    debug_object_active_state(head, &rcuhead_debug_descr,
81                  STATE_RCU_HEAD_QUEUED,
82                  STATE_RCU_HEAD_READY);
83    debug_object_deactivate(head, &rcuhead_debug_descr);
84}
85#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
86static inline void debug_rcu_head_queue(struct rcu_head *head)
87{
88}
89
90static inline void debug_rcu_head_unqueue(struct rcu_head *head)
91{
92}
93#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
94
95extern void kfree(const void *);
96
97static inline bool __rcu_reclaim(char *rn, struct rcu_head *head)
98{
99    unsigned long offset = (unsigned long)head->func;
100
101    if (__is_kfree_rcu_offset(offset)) {
102        RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
103        kfree((void *)head - offset);
104        return 1;
105    } else {
106        RCU_TRACE(trace_rcu_invoke_callback(rn, head));
107        head->func(head);
108        return 0;
109    }
110}
111
112#endif /* __LINUX_RCU_H */
113

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