bf16c50390
implementation is by no means perfect as far as some of the algorithms that it uses and the fact that it is missing some functionality (try locks and upgrades/downgrades are not there yet), however it does seem to work in my local testing. There is more detail in the comments in the code, but the short version follows. A reader/writer lock is very much like a regular mutex: it cannot be held across a voluntary sleep; it can be acquired in an interrupt thread; if the lock is held by a writer then the priority of any threads that block on the lock will be lent to the owner; the simple case lock operations all are done in a single atomic op. It also shares some similiarities with sx locks: it supports reader/writer semantics (multiple readers, but single writers); readers are allowed to recurse, but writers are not. We can extend this implementation further by either improving algorithms or adding new functionality, but this should at least give us a base to work with now. Reviewed by: arch (in theory) Tested on: i386 (4 cpu box with a kernel module that used 4 threads that randomly chose between read locks and write locks that ran w/o panicing for over a day solid. It usually panic'd within a few seconds when there were bugs during testing. :) The kernel module source is available on request.)
116 lines
3.4 KiB
C
116 lines
3.4 KiB
C
/*-
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* Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the author nor the names of any co-contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* This module holds the global variables and functions used to maintain
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* lock_object structures.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "opt_ddb.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/ktr.h>
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#include <sys/linker_set.h>
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#include <sys/lock.h>
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#ifdef DDB
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#include <ddb/ddb.h>
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#endif
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CTASSERT(LOCK_CLASS_MAX == 15);
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struct lock_class *lock_classes[LOCK_CLASS_MAX + 1] = {
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&lock_class_mtx_spin,
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&lock_class_mtx_sleep,
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&lock_class_sx,
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&lock_class_rw,
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};
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void
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lock_init(struct lock_object *lock, struct lock_class *class, const char *name,
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const char *type, int flags)
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{
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int i;
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/* Check for double-init and zero object. */
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KASSERT(!lock_initalized(lock), ("lock \"%s\" %p already initialized",
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name, lock));
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/* Look up lock class to find its index. */
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for (i = 0; i < LOCK_CLASS_MAX; i++)
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if (lock_classes[i] == class) {
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lock->lo_flags = i << LO_CLASSSHIFT;
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break;
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}
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KASSERT(i < LOCK_CLASS_MAX, ("unknown lock class %p", class));
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/* Initialize the lock object. */
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lock->lo_name = name;
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lock->lo_type = type != NULL ? type : name;
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lock->lo_flags |= flags | LO_INITIALIZED;
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LOCK_LOG_INIT(lock, 0);
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WITNESS_INIT(lock);
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}
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void
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lock_destroy(struct lock_object *lock)
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{
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KASSERT(lock_initalized(lock), ("lock %p is not initialized", lock));
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WITNESS_DESTROY(lock);
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LOCK_LOG_DESTROY(lock, 0);
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lock->lo_flags &= ~LO_INITIALIZED;
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}
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#ifdef DDB
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DB_SHOW_COMMAND(lock, db_show_lock)
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{
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struct lock_object *lock;
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struct lock_class *class;
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if (!have_addr)
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return;
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lock = (struct lock_object *)addr;
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if (LO_CLASSINDEX(lock) > LOCK_CLASS_MAX) {
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db_printf("Unknown lock class: %d\n", LO_CLASSINDEX(lock));
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return;
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}
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class = LOCK_CLASS(lock);
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db_printf(" class: %s\n", class->lc_name);
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db_printf(" name: %s\n", lock->lo_name);
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if (lock->lo_type && lock->lo_type != lock->lo_name)
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db_printf(" type: %s\n", lock->lo_type);
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class->lc_ddb_show(lock);
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}
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#endif
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