2 * SPDX-License-Identifier: BSD-2-Clause
4 * Copyright (c) 2019, 2020 Jeffrey Roberson <jeff@FreeBSD.org>
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
9 * 1. Redistributions of source code must retain the above copyright
10 * notice unmodified, this list of conditions, and the following
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 #ifndef _SYS_SMR_TYPES_H_
29 #define _SYS_SMR_TYPES_H_
34 * SMR Accessors are meant to provide safe access to SMR protected
35 * pointers and prevent misuse and accidental access.
37 * Accessors are grouped by type:
38 * entered - Use while in a read section (between smr_enter/smr_exit())
39 * serialized - Use while holding a lock that serializes writers. Updates
40 * are synchronized with readers via included barriers.
41 * unserialized - Use after the memory is out of scope and not visible to
44 * All acceses include a parameter for an assert to verify the required
45 * synchronization. For example, a writer might use:
47 * smr_serialized_store(pointer, value, mtx_owned(&writelock));
49 * These are only enabled in INVARIANTS kernels.
52 /* Type restricting pointer access to force smr accessors. */
53 #define SMR_POINTER(type) \
55 type __ptr; /* Do not access directly */ \
59 * Read from an SMR protected pointer while in a read section.
61 #define smr_entered_load(p, smr) ({ \
62 SMR_ASSERT(SMR_ENTERED((smr)), "smr_entered_load"); \
63 (__typeof((p)->__ptr))atomic_load_acq_ptr((uintptr_t *)&(p)->__ptr); \
67 * Read from an SMR protected pointer while serialized by an
68 * external mechanism. 'ex' should contain an assert that the
69 * external mechanism is held. i.e. mtx_owned()
71 #define smr_serialized_load(p, ex) ({ \
72 SMR_ASSERT(ex, "smr_serialized_load"); \
73 (__typeof((p)->__ptr))atomic_load_ptr(&(p)->__ptr); \
77 * Store 'v' to an SMR protected pointer while serialized by an
78 * external mechanism. 'ex' should contain an assert that the
79 * external mechanism is held. i.e. mtx_owned()
81 * Writers that are serialized with mutual exclusion or on a single
82 * thread should use smr_serialized_store() rather than swap.
84 #define smr_serialized_store(p, v, ex) do { \
85 SMR_ASSERT(ex, "smr_serialized_store"); \
86 __typeof((p)->__ptr) _v = (v); \
87 atomic_store_rel_ptr((uintptr_t *)&(p)->__ptr, (uintptr_t)_v); \
91 * swap 'v' with an SMR protected pointer and return the old value
92 * while serialized by an external mechanism. 'ex' should contain
93 * an assert that the external mechanism is provided. i.e. mtx_owned()
95 * Swap permits multiple writers to update a pointer concurrently.
97 #define smr_serialized_swap(p, v, ex) ({ \
98 SMR_ASSERT(ex, "smr_serialized_swap"); \
99 __typeof((p)->__ptr) _v = (v); \
100 /* Release barrier guarantees contents are visible to reader */ \
101 atomic_thread_fence_rel(); \
102 (__typeof((p)->__ptr))atomic_swap_ptr( \
103 (uintptr_t *)&(p)->__ptr, (uintptr_t)_v); \
107 * Read from an SMR protected pointer when no serialization is required
108 * such as in the destructor callback or when the caller guarantees other
111 #define smr_unserialized_load(p, ex) ({ \
112 SMR_ASSERT(ex, "smr_unserialized_load"); \
113 (__typeof((p)->__ptr))atomic_load_ptr(&(p)->__ptr); \
117 * Store to an SMR protected pointer when no serialiation is required
118 * such as in the destructor callback or when the caller guarantees other
121 #define smr_unserialized_store(p, v, ex) do { \
122 SMR_ASSERT(ex, "smr_unserialized_store"); \
123 __typeof((p)->__ptr) _v = (v); \
124 atomic_store_ptr((uintptr_t *)&(p)->__ptr, (uintptr_t)_v); \
130 * Load an SMR protected pointer when accessing kernel data structures through
133 #define smr_kvm_load(p) ((p)->__ptr)
135 #endif /* !_KERNEL */
136 #endif /* !_SYS_SMR_TYPES_H_ */