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      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 
     48 struct pserialize {
     49 	char			psz_dummy;
     50 };
     51 
     52 static kmutex_t			psz_lock	__cacheline_aligned;
     53 static struct evcnt		psz_ev_excl	__cacheline_aligned =
     54     EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "pserialize", "exclusive access");
     55 EVCNT_ATTACH_STATIC(psz_ev_excl);
     56 
     57 /*
     58  * pserialize_init:
     59  *
     60  *	Initialize passive serialization structures.
     61  */
     62 void
     63 pserialize_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  */
     74 pserialize_t
     75 pserialize_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  */
     88 void
     89 pserialize_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  */
    100 void
    101 pserialize_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 
    126 int
    127 pserialize_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 
    137 void
    138 pserialize_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  */
    158 bool
    159 pserialize_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  */
    174 bool
    175 pserialize_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