1/*	$NetBSD: subr_pserialize.c,v 1.24 2023/10/04 20:28:06 ad Exp $	*/
2
3/*-
4 * Copyright (c) 2010, 2011, 2023 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
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.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
17 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
18 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
19 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
20 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 */
28
29/*
30 * Passive serialization.
31 */
32
33#include <sys/cdefs.h>
34__KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.24 2023/10/04 20:28:06 ad Exp $");
35
36#include <sys/param.h>
37
38#include <sys/atomic.h>
39#include <sys/cpu.h>
40#include <sys/evcnt.h>
41#include <sys/kernel.h>
42#include <sys/kmem.h>
43#include <sys/lwp.h>
44#include <sys/mutex.h>
45#include <sys/pserialize.h>
46#include <sys/xcall.h>
47
48struct pserialize {
49	char			psz_dummy;
50};
51
52static kmutex_t			psz_lock	__cacheline_aligned;
53static struct evcnt		psz_ev_excl	__cacheline_aligned =
54    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "pserialize", "exclusive access");
55EVCNT_ATTACH_STATIC(psz_ev_excl);
56
57/*
58 * pserialize_init:
59 *
60 *	Initialize passive serialization structures.
61 */
62void
63pserialize_init(void)
64{
65
66	mutex_init(&psz_lock, MUTEX_DEFAULT, IPL_NONE);
67}
68
69/*
70 * pserialize_create:
71 *
72 *	Create and initialize a passive serialization object.
73 */
74pserialize_t
75pserialize_create(void)
76{
77	pserialize_t psz;
78
79	psz = kmem_zalloc(sizeof(*psz), KM_SLEEP);
80	return psz;
81}
82
83/*
84 * pserialize_destroy:
85 *
86 *	Destroy a passive serialization object.
87 */
88void
89pserialize_destroy(pserialize_t psz)
90{
91
92	kmem_free(psz, sizeof(*psz));
93}
94
95/*
96 * pserialize_perform:
97 *
98 *	Perform the write side of passive serialization.
99 */
100void
101pserialize_perform(pserialize_t psz)
102{
103
104	KASSERT(!cpu_intr_p());
105	KASSERT(!cpu_softintr_p());
106
107	if (__predict_false(panicstr != NULL)) {
108		return;
109	}
110
111	if (__predict_false(mp_online == false)) {
112		psz_ev_excl.ev_count++;
113		return;
114	}
115
116	/*
117	 * Broadcast a NOP to all CPUs and wait until all of them complete.
118	 */
119	xc_barrier(XC_HIGHPRI);
120
121	mutex_enter(&psz_lock);
122	psz_ev_excl.ev_count++;
123	mutex_exit(&psz_lock);
124}
125
126int
127pserialize_read_enter(void)
128{
129	int s;
130
131	s = splsoftserial();
132	curcpu()->ci_psz_read_depth++;
133	__insn_barrier();
134	return s;
135}
136
137void
138pserialize_read_exit(int s)
139{
140
141	KASSERT(__predict_false(cold) || kpreempt_disabled());
142
143	__insn_barrier();
144	if (__predict_false(curcpu()->ci_psz_read_depth-- == 0))
145		panic("mismatching pserialize_read_exit()");
146	splx(s);
147}
148
149/*
150 * pserialize_in_read_section:
151 *
152 *	True if the caller is in a pserialize read section.  To be used
153 *	only for diagnostic assertions where we want to guarantee the
154 *	condition like:
155 *
156 *		KASSERT(pserialize_in_read_section());
157 */
158bool
159pserialize_in_read_section(void)
160{
161
162	return kpreempt_disabled() && curcpu()->ci_psz_read_depth > 0;
163}
164
165/*
166 * pserialize_not_in_read_section:
167 *
168 *	True if the caller is not in a pserialize read section.  To be
169 *	used only for diagnostic assertions where we want to guarantee
170 *	the condition like:
171 *
172 *		KASSERT(pserialize_not_in_read_section());
173 */
174bool
175pserialize_not_in_read_section(void)
176{
177	bool notin;
178	long pctr;
179
180	pctr = lwp_pctr();
181	notin = __predict_true(curcpu()->ci_psz_read_depth == 0);
182
183	/*
184	 * If we had a context switch, we're definitely not in a
185	 * pserialize read section because pserialize read sections
186	 * block preemption.
187	 */
188	if (__predict_false(pctr != lwp_pctr()))
189		notin = true;
190
191	return notin;
192}
193