149 lines
3.9 KiB
C
149 lines
3.9 KiB
C
/*
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* Copyright (c) 2009
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* The President and Fellows of Harvard College.
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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 University nor the names of its 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 UNIVERSITY 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 UNIVERSITY 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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/* Make sure to build out-of-line versions of inline functions */
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#define SPINLOCK_INLINE /* empty */
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#define MEMBAR_INLINE /* empty */
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#include <types.h>
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#include <lib.h>
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#include <cpu.h>
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#include <spl.h>
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#include <spinlock.h>
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#include <membar.h>
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#include <current.h> /* for curcpu */
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/*
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* Spinlocks.
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*/
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/*
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* Initialize spinlock.
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*/
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void
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spinlock_init(struct spinlock *splk)
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{
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spinlock_data_set(&splk->splk_lock, 0);
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splk->splk_holder = NULL;
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}
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/*
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* Clean up spinlock.
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*/
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void
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spinlock_cleanup(struct spinlock *splk)
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{
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KASSERT(splk->splk_holder == NULL);
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KASSERT(spinlock_data_get(&splk->splk_lock) == 0);
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}
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/*
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* Get the lock.
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*
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* First disable interrupts (otherwise, if we get a timer interrupt we
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* might come back to this lock and deadlock), then use a machine-level
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* atomic operation to wait for the lock to be free.
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*/
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void
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spinlock_acquire(struct spinlock *splk)
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{
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struct cpu *mycpu;
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splraise(IPL_NONE, IPL_HIGH);
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/* this must work before curcpu initialization */
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if (CURCPU_EXISTS()) {
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mycpu = curcpu->c_self;
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if (splk->splk_holder == mycpu) {
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panic("Deadlock on spinlock %p\n", splk);
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}
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mycpu->c_spinlocks++;
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}
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else {
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mycpu = NULL;
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}
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while (1) {
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/*
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* Do test-test-and-set, that is, read first before
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* doing test-and-set, to reduce bus contention.
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*
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* Test-and-set is a machine-level atomic operation
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* that writes 1 into the lock word and returns the
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* previous value. If that value was 0, the lock was
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* previously unheld and we now own it. If it was 1,
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* we don't.
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*/
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if (spinlock_data_get(&splk->splk_lock) != 0) {
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continue;
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}
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if (spinlock_data_testandset(&splk->splk_lock) != 0) {
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continue;
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}
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break;
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}
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membar_store_any();
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splk->splk_holder = mycpu;
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}
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/*
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* Release the lock.
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*/
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void
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spinlock_release(struct spinlock *splk)
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{
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/* this must work before curcpu initialization */
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if (CURCPU_EXISTS()) {
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KASSERT(splk->splk_holder == curcpu->c_self);
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KASSERT(curcpu->c_spinlocks > 0);
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curcpu->c_spinlocks--;
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}
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splk->splk_holder = NULL;
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membar_any_store();
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spinlock_data_set(&splk->splk_lock, 0);
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spllower(IPL_HIGH, IPL_NONE);
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}
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/*
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* Check if the current cpu holds the lock.
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*/
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bool
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spinlock_do_i_hold(struct spinlock *splk)
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{
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if (!CURCPU_EXISTS()) {
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return true;
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}
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/* Assume we can read splk_holder atomically enough for this to work */
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return (splk->splk_holder == curcpu->c_self);
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}
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