920 lines
23 KiB
C
920 lines
23 KiB
C
/* $NetBSD: kern_mutex.c,v 1.13 2007/03/12 22:34:08 ad Exp $ */
|
|
|
|
/*-
|
|
* Copyright (c) 2002, 2006, 2007 The NetBSD Foundation, Inc.
|
|
* All rights reserved.
|
|
*
|
|
* This code is derived from software contributed to The NetBSD Foundation
|
|
* by Jason R. Thorpe and Andrew Doran.
|
|
*
|
|
* Redistribution and use in source and binary forms, with or without
|
|
* modification, are permitted provided that the following conditions
|
|
* are met:
|
|
* 1. Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimer.
|
|
* 2. Redistributions in binary form must reproduce the above copyright
|
|
* notice, this list of conditions and the following disclaimer in the
|
|
* documentation and/or other materials provided with the distribution.
|
|
* 3. All advertising materials mentioning features or use of this software
|
|
* must display the following acknowledgement:
|
|
* This product includes software developed by the NetBSD
|
|
* Foundation, Inc. and its contributors.
|
|
* 4. Neither the name of The NetBSD Foundation nor the names of its
|
|
* contributors may be used to endorse or promote products derived
|
|
* from this software without specific prior written permission.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
|
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
|
|
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
|
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
|
|
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
|
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
|
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
|
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
* POSSIBILITY OF SUCH DAMAGE.
|
|
*/
|
|
|
|
/*
|
|
* Kernel mutex implementation, modeled after those found in Solaris,
|
|
* a description of which can be found in:
|
|
*
|
|
* Solaris Internals: Core Kernel Architecture, Jim Mauro and
|
|
* Richard McDougall.
|
|
*/
|
|
|
|
#include "opt_multiprocessor.h"
|
|
|
|
#define __MUTEX_PRIVATE
|
|
|
|
#include <sys/cdefs.h>
|
|
__KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.13 2007/03/12 22:34:08 ad Exp $");
|
|
|
|
#include <sys/param.h>
|
|
#include <sys/proc.h>
|
|
#include <sys/mutex.h>
|
|
#include <sys/sched.h>
|
|
#include <sys/sleepq.h>
|
|
#include <sys/systm.h>
|
|
#include <sys/lockdebug.h>
|
|
#include <sys/kernel.h>
|
|
|
|
#include <dev/lockstat.h>
|
|
|
|
#include <machine/intr.h>
|
|
|
|
/*
|
|
* When not running a debug kernel, spin mutexes are not much
|
|
* more than an splraiseipl() and splx() pair.
|
|
*/
|
|
|
|
#if defined(DIAGNOSTIC) || defined(MULTIPROCESSOR) || defined(LOCKDEBUG)
|
|
#define FULL
|
|
#endif
|
|
|
|
/*
|
|
* Debugging support.
|
|
*/
|
|
|
|
#define MUTEX_WANTLOCK(mtx) \
|
|
LOCKDEBUG_WANTLOCK(MUTEX_GETID(mtx), \
|
|
(uintptr_t)__builtin_return_address(0), 0)
|
|
#define MUTEX_LOCKED(mtx) \
|
|
LOCKDEBUG_LOCKED(MUTEX_GETID(mtx), \
|
|
(uintptr_t)__builtin_return_address(0), 0)
|
|
#define MUTEX_UNLOCKED(mtx) \
|
|
LOCKDEBUG_UNLOCKED(MUTEX_GETID(mtx), \
|
|
(uintptr_t)__builtin_return_address(0), 0)
|
|
#define MUTEX_ABORT(mtx, msg) \
|
|
mutex_abort(mtx, __FUNCTION__, msg)
|
|
|
|
#if defined(LOCKDEBUG)
|
|
|
|
#define MUTEX_DASSERT(mtx, cond) \
|
|
do { \
|
|
if (!(cond)) \
|
|
MUTEX_ABORT(mtx, "assertion failed: " #cond); \
|
|
} while (/* CONSTCOND */ 0);
|
|
|
|
#else /* LOCKDEBUG */
|
|
|
|
#define MUTEX_DASSERT(mtx, cond) /* nothing */
|
|
|
|
#endif /* LOCKDEBUG */
|
|
|
|
#if defined(DIAGNOSTIC)
|
|
|
|
#define MUTEX_ASSERT(mtx, cond) \
|
|
do { \
|
|
if (!(cond)) \
|
|
MUTEX_ABORT(mtx, "assertion failed: " #cond); \
|
|
} while (/* CONSTCOND */ 0)
|
|
|
|
#else /* DIAGNOSTIC */
|
|
|
|
#define MUTEX_ASSERT(mtx, cond) /* nothing */
|
|
|
|
#endif /* DIAGNOSTIC */
|
|
|
|
/*
|
|
* Spin mutex SPL save / restore.
|
|
*/
|
|
#ifndef MUTEX_COUNT_BIAS
|
|
#define MUTEX_COUNT_BIAS 0
|
|
#endif
|
|
|
|
#define MUTEX_SPIN_SPLRAISE(mtx) \
|
|
do { \
|
|
struct cpu_info *x__ci = curcpu(); \
|
|
int x__cnt, s; \
|
|
x__cnt = x__ci->ci_mtx_count--; \
|
|
s = splraiseipl(mtx->mtx_ipl); \
|
|
if (x__cnt == MUTEX_COUNT_BIAS) \
|
|
x__ci->ci_mtx_oldspl = (s); \
|
|
} while (/* CONSTCOND */ 0)
|
|
|
|
#define MUTEX_SPIN_SPLRESTORE(mtx) \
|
|
do { \
|
|
struct cpu_info *x__ci = curcpu(); \
|
|
int s = x__ci->ci_mtx_oldspl; \
|
|
__insn_barrier(); \
|
|
if (++(x__ci->ci_mtx_count) == MUTEX_COUNT_BIAS) \
|
|
splx(s); \
|
|
} while (/* CONSTCOND */ 0)
|
|
|
|
/*
|
|
* For architectures that provide 'simple' mutexes: they provide a
|
|
* CAS function that is either MP-safe, or does not need to be MP
|
|
* safe. Adaptive mutexes on these architectures do not require an
|
|
* additional interlock.
|
|
*/
|
|
|
|
#ifdef __HAVE_SIMPLE_MUTEXES
|
|
|
|
#define MUTEX_OWNER(owner) \
|
|
(owner & MUTEX_THREAD)
|
|
#define MUTEX_OWNED(owner) \
|
|
(owner != 0)
|
|
#define MUTEX_HAS_WAITERS(mtx) \
|
|
(((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0)
|
|
|
|
#define MUTEX_INITIALIZE_ADAPTIVE(mtx, id) \
|
|
do { \
|
|
(mtx)->mtx_id = (id); \
|
|
} while (/* CONSTCOND */ 0);
|
|
|
|
#define MUTEX_INITIALIZE_SPIN(mtx, id, ipl) \
|
|
do { \
|
|
(mtx)->mtx_owner = MUTEX_BIT_SPIN; \
|
|
(mtx)->mtx_ipl = makeiplcookie((ipl)); \
|
|
(mtx)->mtx_id = (id); \
|
|
__cpu_simple_lock_init(&(mtx)->mtx_lock); \
|
|
} while (/* CONSTCOND */ 0)
|
|
|
|
#define MUTEX_DESTROY(mtx) \
|
|
do { \
|
|
(mtx)->mtx_owner = MUTEX_THREAD; \
|
|
(mtx)->mtx_id = -1; \
|
|
} while (/* CONSTCOND */ 0);
|
|
|
|
#define MUTEX_SPIN_P(mtx) \
|
|
(((mtx)->mtx_owner & MUTEX_BIT_SPIN) != 0)
|
|
#define MUTEX_ADAPTIVE_P(mtx) \
|
|
(((mtx)->mtx_owner & MUTEX_BIT_SPIN) == 0)
|
|
|
|
#define MUTEX_GETID(mtx) ((mtx)->mtx_id)
|
|
|
|
static inline int
|
|
MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
|
|
{
|
|
int rv;
|
|
rv = MUTEX_CAS(&mtx->mtx_owner, 0UL, curthread);
|
|
MUTEX_RECEIVE(mtx);
|
|
return rv;
|
|
}
|
|
|
|
static inline int
|
|
MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
|
|
{
|
|
int rv;
|
|
rv = MUTEX_CAS(&mtx->mtx_owner, owner, owner | MUTEX_BIT_WAITERS);
|
|
MUTEX_RECEIVE(mtx);
|
|
return rv;
|
|
}
|
|
|
|
static inline void
|
|
MUTEX_RELEASE(kmutex_t *mtx)
|
|
{
|
|
MUTEX_GIVE(mtx);
|
|
mtx->mtx_owner = 0;
|
|
}
|
|
|
|
static inline void
|
|
MUTEX_CLEAR_WAITERS(kmutex_t *mtx)
|
|
{
|
|
/* nothing */
|
|
}
|
|
#endif /* __HAVE_SIMPLE_MUTEXES */
|
|
|
|
/*
|
|
* Patch in stubs via strong alias where they are not available.
|
|
*/
|
|
|
|
#if defined(LOCKDEBUG)
|
|
#undef __HAVE_MUTEX_STUBS
|
|
#undef __HAVE_SPIN_MUTEX_STUBS
|
|
#endif
|
|
|
|
#ifndef __HAVE_MUTEX_STUBS
|
|
__strong_alias(mutex_enter,mutex_vector_enter);
|
|
__strong_alias(mutex_exit,mutex_vector_exit);
|
|
#endif
|
|
|
|
#ifndef __HAVE_SPIN_MUTEX_STUBS
|
|
__strong_alias(mutex_spin_enter,mutex_vector_enter);
|
|
__strong_alias(mutex_spin_exit,mutex_vector_exit);
|
|
#endif
|
|
|
|
void mutex_abort(kmutex_t *, const char *, const char *);
|
|
void mutex_dump(volatile void *);
|
|
int mutex_onproc(uintptr_t, struct cpu_info **);
|
|
static struct lwp *mutex_owner(wchan_t);
|
|
|
|
lockops_t mutex_spin_lockops = {
|
|
"Mutex",
|
|
0,
|
|
mutex_dump
|
|
};
|
|
|
|
lockops_t mutex_adaptive_lockops = {
|
|
"Mutex",
|
|
1,
|
|
mutex_dump
|
|
};
|
|
|
|
syncobj_t mutex_syncobj = {
|
|
SOBJ_SLEEPQ_SORTED,
|
|
turnstile_unsleep,
|
|
turnstile_changepri,
|
|
sleepq_lendpri,
|
|
mutex_owner,
|
|
};
|
|
|
|
/*
|
|
* mutex_dump:
|
|
*
|
|
* Dump the contents of a mutex structure.
|
|
*/
|
|
void
|
|
mutex_dump(volatile void *cookie)
|
|
{
|
|
volatile kmutex_t *mtx = cookie;
|
|
|
|
printf_nolog("owner field : %#018lx wait/spin: %16d/%d\n",
|
|
(long)MUTEX_OWNER(mtx->mtx_owner), MUTEX_HAS_WAITERS(mtx),
|
|
MUTEX_SPIN_P(mtx));
|
|
}
|
|
|
|
/*
|
|
* mutex_abort:
|
|
*
|
|
* Dump information about an error and panic the system. This
|
|
* generates a lot of machine code in the DIAGNOSTIC case, so
|
|
* we ask the compiler to not inline it.
|
|
*/
|
|
|
|
#if __GNUC_PREREQ__(3, 0)
|
|
__attribute ((noinline)) __attribute ((noreturn))
|
|
#endif
|
|
void
|
|
mutex_abort(kmutex_t *mtx, const char *func, const char *msg)
|
|
{
|
|
|
|
LOCKDEBUG_ABORT(MUTEX_GETID(mtx), mtx, (MUTEX_SPIN_P(mtx) ?
|
|
&mutex_spin_lockops : &mutex_adaptive_lockops), func, msg);
|
|
/* NOTREACHED */
|
|
}
|
|
|
|
/*
|
|
* mutex_init:
|
|
*
|
|
* Initialize a mutex for use. Note that adaptive mutexes are in
|
|
* essence spin mutexes that can sleep to avoid deadlock and wasting
|
|
* CPU time. We can't easily provide a type of mutex that always
|
|
* sleeps - see comments in mutex_vector_enter() about releasing
|
|
* mutexes unlocked.
|
|
*/
|
|
void
|
|
mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl)
|
|
{
|
|
u_int id;
|
|
|
|
memset(mtx, 0, sizeof(*mtx));
|
|
|
|
if (type == MUTEX_DRIVER)
|
|
type = (ipl == IPL_NONE ? MUTEX_ADAPTIVE : MUTEX_SPIN);
|
|
|
|
switch (type) {
|
|
case MUTEX_NODEBUG:
|
|
KASSERT(ipl == IPL_NONE);
|
|
id = LOCKDEBUG_ALLOC(mtx, NULL);
|
|
MUTEX_INITIALIZE_ADAPTIVE(mtx, id);
|
|
break;
|
|
case MUTEX_ADAPTIVE:
|
|
case MUTEX_DEFAULT:
|
|
KASSERT(ipl == IPL_NONE);
|
|
id = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops);
|
|
MUTEX_INITIALIZE_ADAPTIVE(mtx, id);
|
|
break;
|
|
case MUTEX_SPIN:
|
|
id = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops);
|
|
MUTEX_INITIALIZE_SPIN(mtx, id, ipl);
|
|
break;
|
|
default:
|
|
panic("mutex_init: impossible type");
|
|
break;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* mutex_destroy:
|
|
*
|
|
* Tear down a mutex.
|
|
*/
|
|
void
|
|
mutex_destroy(kmutex_t *mtx)
|
|
{
|
|
|
|
if (MUTEX_ADAPTIVE_P(mtx)) {
|
|
MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) &&
|
|
!MUTEX_HAS_WAITERS(mtx));
|
|
} else {
|
|
MUTEX_ASSERT(mtx, mtx->mtx_lock != __SIMPLELOCK_LOCKED);
|
|
}
|
|
|
|
LOCKDEBUG_FREE(mtx, MUTEX_GETID(mtx));
|
|
MUTEX_DESTROY(mtx);
|
|
}
|
|
|
|
/*
|
|
* mutex_onproc:
|
|
*
|
|
* Return true if an adaptive mutex owner is running on a CPU in the
|
|
* system. If the target is waiting on the kernel big lock, then we
|
|
* return false immediately. This is necessary to avoid deadlock
|
|
* against the big lock.
|
|
*
|
|
* Note that we can't use the mutex owner field as an LWP pointer. We
|
|
* don't have full control over the timing of our execution, and so the
|
|
* pointer could be completely invalid by the time we dereference it.
|
|
*
|
|
* XXX This should be optimised further to reduce potential cache line
|
|
* ping-ponging and skewing of the spin time while busy waiting.
|
|
*/
|
|
#ifdef MULTIPROCESSOR
|
|
int
|
|
mutex_onproc(uintptr_t owner, struct cpu_info **cip)
|
|
{
|
|
CPU_INFO_ITERATOR cii;
|
|
struct cpu_info *ci;
|
|
struct lwp *l;
|
|
|
|
if (!MUTEX_OWNED(owner))
|
|
return 0;
|
|
l = (struct lwp *)MUTEX_OWNER(owner);
|
|
|
|
if ((ci = *cip) != NULL && ci->ci_curlwp == l)
|
|
return ci->ci_biglock_wanted != l;
|
|
|
|
for (CPU_INFO_FOREACH(cii, ci)) {
|
|
if (ci->ci_curlwp == l) {
|
|
*cip = ci;
|
|
return ci->ci_biglock_wanted != l;
|
|
}
|
|
}
|
|
|
|
*cip = NULL;
|
|
return 0;
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* mutex_vector_enter:
|
|
*
|
|
* Support routine for mutex_enter() that must handles all cases. In
|
|
* the LOCKDEBUG case, mutex_enter() is always aliased here, even if
|
|
* fast-path stubs are available. If an mutex_spin_enter() stub is
|
|
* not available, then it is also aliased directly here.
|
|
*/
|
|
void
|
|
mutex_vector_enter(kmutex_t *mtx)
|
|
{
|
|
uintptr_t owner, curthread;
|
|
turnstile_t *ts;
|
|
#ifdef MULTIPROCESSOR
|
|
struct cpu_info *ci = NULL;
|
|
u_int count;
|
|
#endif
|
|
LOCKSTAT_COUNTER(spincnt);
|
|
LOCKSTAT_COUNTER(slpcnt);
|
|
LOCKSTAT_TIMER(spintime);
|
|
LOCKSTAT_TIMER(slptime);
|
|
LOCKSTAT_FLAG(lsflag);
|
|
|
|
/*
|
|
* Handle spin mutexes.
|
|
*/
|
|
if (MUTEX_SPIN_P(mtx)) {
|
|
#if defined(LOCKDEBUG) && defined(MULTIPROCESSOR)
|
|
u_int spins = 0;
|
|
#endif
|
|
MUTEX_SPIN_SPLRAISE(mtx);
|
|
MUTEX_WANTLOCK(mtx);
|
|
#ifdef FULL
|
|
if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
|
|
MUTEX_LOCKED(mtx);
|
|
return;
|
|
}
|
|
#if !defined(MULTIPROCESSOR)
|
|
MUTEX_ABORT(mtx, "locking against myself");
|
|
#else /* !MULTIPROCESSOR */
|
|
|
|
LOCKSTAT_ENTER(lsflag);
|
|
LOCKSTAT_START_TIMER(lsflag, spintime);
|
|
count = SPINLOCK_BACKOFF_MIN;
|
|
|
|
/*
|
|
* Spin testing the lock word and do exponential backoff
|
|
* to reduce cache line ping-ponging between CPUs.
|
|
*/
|
|
do {
|
|
if (panicstr != NULL)
|
|
break;
|
|
while (mtx->mtx_lock == __SIMPLELOCK_LOCKED) {
|
|
SPINLOCK_BACKOFF(count);
|
|
#ifdef LOCKDEBUG
|
|
if (SPINLOCK_SPINOUT(spins))
|
|
MUTEX_ABORT(mtx, "spinout");
|
|
#endif /* LOCKDEBUG */
|
|
}
|
|
} while (!__cpu_simple_lock_try(&mtx->mtx_lock));
|
|
|
|
if (count != SPINLOCK_BACKOFF_MIN) {
|
|
LOCKSTAT_STOP_TIMER(lsflag, spintime);
|
|
LOCKSTAT_EVENT(lsflag, mtx,
|
|
LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
|
|
}
|
|
LOCKSTAT_EXIT(lsflag);
|
|
#endif /* !MULTIPROCESSOR */
|
|
#endif /* FULL */
|
|
MUTEX_LOCKED(mtx);
|
|
return;
|
|
}
|
|
|
|
curthread = (uintptr_t)curlwp;
|
|
|
|
MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
|
|
MUTEX_ASSERT(mtx, curthread != 0);
|
|
MUTEX_WANTLOCK(mtx);
|
|
|
|
#ifdef LOCKDEBUG
|
|
if (panicstr == NULL) {
|
|
simple_lock_only_held(NULL, "mutex_enter");
|
|
#ifdef MULTIPROCESSOR
|
|
LOCKDEBUG_BARRIER(&kernel_lock, 1);
|
|
#else
|
|
LOCKDEBUG_BARRIER(NULL, 1);
|
|
#endif
|
|
}
|
|
#endif
|
|
|
|
LOCKSTAT_ENTER(lsflag);
|
|
|
|
/*
|
|
* Adaptive mutex; spin trying to acquire the mutex. If we
|
|
* determine that the owner is not running on a processor,
|
|
* then we stop spinning, and sleep instead.
|
|
*/
|
|
for (;;) {
|
|
owner = mtx->mtx_owner;
|
|
if (!MUTEX_OWNED(owner)) {
|
|
/*
|
|
* Mutex owner clear could mean two things:
|
|
*
|
|
* * The mutex has been released.
|
|
* * The owner field hasn't been set yet.
|
|
*
|
|
* Try to acquire it again. If that fails,
|
|
* we'll just loop again.
|
|
*/
|
|
if (MUTEX_ACQUIRE(mtx, curthread))
|
|
break;
|
|
continue;
|
|
}
|
|
|
|
if (panicstr != NULL)
|
|
return;
|
|
if (MUTEX_OWNER(owner) == curthread)
|
|
MUTEX_ABORT(mtx, "locking against myself");
|
|
|
|
#ifdef MULTIPROCESSOR
|
|
/*
|
|
* Check to see if the owner is running on a processor.
|
|
* If so, then we should just spin, as the owner will
|
|
* likely release the lock very soon.
|
|
*/
|
|
if (mutex_onproc(owner, &ci)) {
|
|
LOCKSTAT_START_TIMER(lsflag, spintime);
|
|
count = SPINLOCK_BACKOFF_MIN;
|
|
for (;;) {
|
|
owner = mtx->mtx_owner;
|
|
if (!mutex_onproc(owner, &ci))
|
|
break;
|
|
SPINLOCK_BACKOFF(count);
|
|
}
|
|
LOCKSTAT_STOP_TIMER(lsflag, spintime);
|
|
LOCKSTAT_COUNT(spincnt, 1);
|
|
if (!MUTEX_OWNED(owner))
|
|
continue;
|
|
}
|
|
#endif
|
|
|
|
ts = turnstile_lookup(mtx);
|
|
|
|
/*
|
|
* Once we have the turnstile chain interlock, mark the
|
|
* mutex has having waiters. If that fails, spin again:
|
|
* chances are that the mutex has been released.
|
|
*/
|
|
if (!MUTEX_SET_WAITERS(mtx, owner)) {
|
|
turnstile_exit(mtx);
|
|
continue;
|
|
}
|
|
|
|
#ifdef MULTIPROCESSOR
|
|
/*
|
|
* mutex_exit() is permitted to release the mutex without
|
|
* any interlocking instructions, and the following can
|
|
* occur as a result:
|
|
*
|
|
* CPU 1: MUTEX_SET_WAITERS() CPU2: mutex_exit()
|
|
* ---------------------------- ----------------------------
|
|
* .. acquire cache line
|
|
* .. test for waiters
|
|
* acquire cache line <- lose cache line
|
|
* lock cache line ..
|
|
* verify mutex is held ..
|
|
* set waiters ..
|
|
* unlock cache line ..
|
|
* lose cache line -> acquire cache line
|
|
* .. clear lock word, waiters
|
|
* return success
|
|
*
|
|
* There is a another race that can occur: a third CPU could
|
|
* acquire the mutex as soon as it is released. Since
|
|
* adaptive mutexes are primarily spin mutexes, this is not
|
|
* something that we need to worry about too much. What we
|
|
* do need to ensure is that the waiters bit gets set.
|
|
*
|
|
* To allow the unlocked release, we need to make some
|
|
* assumptions here:
|
|
*
|
|
* o Release is the only non-atomic/unlocked operation
|
|
* that can be performed on the mutex. (It must still
|
|
* be atomic on the local CPU, e.g. in case interrupted
|
|
* or preempted).
|
|
*
|
|
* o At any given time, MUTEX_SET_WAITERS() can only ever
|
|
* be in progress on one CPU in the system - guarenteed
|
|
* by the turnstile chain lock.
|
|
*
|
|
* o No other operations other than MUTEX_SET_WAITERS()
|
|
* and release can modify a mutex with a non-zero
|
|
* owner field.
|
|
*
|
|
* o The result of a successful MUTEX_SET_WAITERS() call
|
|
* is an unbuffered write that is immediately visible
|
|
* to all other processors in the system.
|
|
*
|
|
* o If the holding LWP switches away, it posts a store
|
|
* fence before changing curlwp, ensuring that any
|
|
* overwrite of the mutex waiters flag by mutex_exit()
|
|
* completes before the modification of curlwp becomes
|
|
* visible to this CPU.
|
|
*
|
|
* o cpu_switch() posts a store fence before setting curlwp
|
|
* and before resuming execution of an LWP.
|
|
*
|
|
* o _kernel_lock() posts a store fence before setting
|
|
* curcpu()->ci_biglock_wanted, and after clearing it.
|
|
* This ensures that any overwrite of the mutex waiters
|
|
* flag by mutex_exit() completes before the modification
|
|
* of ci_biglock_wanted becomes visible.
|
|
*
|
|
* We now post a read memory barrier (after setting the
|
|
* waiters field) and check the lock holder's status again.
|
|
* Some of the possible outcomes (not an exhaustive list):
|
|
*
|
|
* 1. The onproc check returns true: the holding LWP is
|
|
* running again. The lock may be released soon and
|
|
* we should spin. Importantly, we can't trust the
|
|
* value of the waiters flag.
|
|
*
|
|
* 2. The onproc check returns false: the holding LWP is
|
|
* not running. We now have the oppertunity to check
|
|
* if mutex_exit() has blatted the modifications made
|
|
* by MUTEX_SET_WAITERS().
|
|
*
|
|
* 3. The onproc check returns false: the holding LWP may
|
|
* or may not be running. It has context switched at
|
|
* some point during our check. Again, we have the
|
|
* chance to see if the waiters bit is still set or
|
|
* has been overwritten.
|
|
*
|
|
* 4. The onproc check returns false: the holding LWP is
|
|
* running on a CPU, but wants the big lock. It's OK
|
|
* to check the waiters field in this case.
|
|
*
|
|
* 5. The has-waiters check fails: the mutex has been
|
|
* released, the waiters flag cleared and another LWP
|
|
* now owns the mutex.
|
|
*
|
|
* 6. The has-waiters check fails: the mutex has been
|
|
* released.
|
|
*
|
|
* If the waiters bit is not set it's unsafe to go asleep,
|
|
* as we might never be awoken.
|
|
*/
|
|
if ((mb_read(), mutex_onproc(owner, &ci)) ||
|
|
(mb_read(), !MUTEX_HAS_WAITERS(mtx))) {
|
|
turnstile_exit(mtx);
|
|
continue;
|
|
}
|
|
#endif /* MULTIPROCESSOR */
|
|
|
|
LOCKSTAT_START_TIMER(lsflag, slptime);
|
|
|
|
turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj);
|
|
|
|
LOCKSTAT_STOP_TIMER(lsflag, slptime);
|
|
LOCKSTAT_COUNT(slpcnt, 1);
|
|
|
|
turnstile_unblock();
|
|
}
|
|
|
|
LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1,
|
|
slpcnt, slptime);
|
|
LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN,
|
|
spincnt, spintime);
|
|
LOCKSTAT_EXIT(lsflag);
|
|
|
|
MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
|
|
MUTEX_LOCKED(mtx);
|
|
}
|
|
|
|
/*
|
|
* mutex_vector_exit:
|
|
*
|
|
* Support routine for mutex_exit() that handles all cases.
|
|
*/
|
|
void
|
|
mutex_vector_exit(kmutex_t *mtx)
|
|
{
|
|
turnstile_t *ts;
|
|
uintptr_t curthread;
|
|
|
|
if (MUTEX_SPIN_P(mtx)) {
|
|
#ifdef FULL
|
|
if (mtx->mtx_lock != __SIMPLELOCK_LOCKED)
|
|
MUTEX_ABORT(mtx, "exiting unheld spin mutex");
|
|
MUTEX_UNLOCKED(mtx);
|
|
__cpu_simple_unlock(&mtx->mtx_lock);
|
|
#endif
|
|
MUTEX_SPIN_SPLRESTORE(mtx);
|
|
return;
|
|
}
|
|
|
|
if (__predict_false((uintptr_t)panicstr | cold)) {
|
|
MUTEX_UNLOCKED(mtx);
|
|
MUTEX_RELEASE(mtx);
|
|
return;
|
|
}
|
|
|
|
curthread = (uintptr_t)curlwp;
|
|
MUTEX_DASSERT(mtx, curthread != 0);
|
|
MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
|
|
MUTEX_UNLOCKED(mtx);
|
|
|
|
/*
|
|
* Get this lock's turnstile. This gets the interlock on
|
|
* the sleep queue. Once we have that, we can clear the
|
|
* lock. If there was no turnstile for the lock, there
|
|
* were no waiters remaining.
|
|
*/
|
|
ts = turnstile_lookup(mtx);
|
|
|
|
if (ts == NULL) {
|
|
MUTEX_RELEASE(mtx);
|
|
turnstile_exit(mtx);
|
|
} else {
|
|
MUTEX_RELEASE(mtx);
|
|
turnstile_wakeup(ts, TS_WRITER_Q,
|
|
TS_WAITERS(ts, TS_WRITER_Q), NULL);
|
|
}
|
|
}
|
|
|
|
#ifndef __HAVE_SIMPLE_MUTEXES
|
|
/*
|
|
* mutex_wakeup:
|
|
*
|
|
* Support routine for mutex_exit() that wakes up all waiters.
|
|
* We assume that the mutex has been released, but it need not
|
|
* be.
|
|
*/
|
|
void
|
|
mutex_wakeup(kmutex_t *mtx)
|
|
{
|
|
turnstile_t *ts;
|
|
|
|
ts = turnstile_lookup(mtx);
|
|
if (ts == NULL) {
|
|
turnstile_exit(mtx);
|
|
return;
|
|
}
|
|
MUTEX_CLEAR_WAITERS(mtx);
|
|
turnstile_wakeup(ts, TS_WRITER_Q, TS_WAITERS(ts, TS_WRITER_Q), NULL);
|
|
}
|
|
#endif /* !__HAVE_SIMPLE_MUTEXES */
|
|
|
|
/*
|
|
* mutex_owned:
|
|
*
|
|
* Return true if the current LWP (adaptive) or CPU (spin)
|
|
* holds the mutex.
|
|
*/
|
|
int
|
|
mutex_owned(kmutex_t *mtx)
|
|
{
|
|
|
|
if (MUTEX_ADAPTIVE_P(mtx))
|
|
return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp;
|
|
#ifdef FULL
|
|
return mtx->mtx_lock == __SIMPLELOCK_LOCKED;
|
|
#else
|
|
return 1;
|
|
#endif
|
|
}
|
|
|
|
/*
|
|
* mutex_owner:
|
|
*
|
|
* Return the current owner of an adaptive mutex. Used for
|
|
* priority inheritance.
|
|
*/
|
|
static struct lwp *
|
|
mutex_owner(wchan_t obj)
|
|
{
|
|
kmutex_t *mtx = (void *)(uintptr_t)obj; /* discard qualifiers */
|
|
|
|
MUTEX_ASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
|
|
return (struct lwp *)MUTEX_OWNER(mtx->mtx_owner);
|
|
}
|
|
|
|
/*
|
|
* mutex_tryenter:
|
|
*
|
|
* Try to acquire the mutex; return non-zero if we did.
|
|
*/
|
|
int
|
|
mutex_tryenter(kmutex_t *mtx)
|
|
{
|
|
uintptr_t curthread;
|
|
|
|
/*
|
|
* Handle spin mutexes.
|
|
*/
|
|
if (MUTEX_SPIN_P(mtx)) {
|
|
MUTEX_SPIN_SPLRAISE(mtx);
|
|
#ifdef FULL
|
|
if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
|
|
MUTEX_WANTLOCK(mtx);
|
|
MUTEX_LOCKED(mtx);
|
|
return 1;
|
|
}
|
|
MUTEX_SPIN_SPLRESTORE(mtx);
|
|
#else
|
|
MUTEX_WANTLOCK(mtx);
|
|
MUTEX_LOCKED(mtx);
|
|
return 1;
|
|
#endif
|
|
} else {
|
|
curthread = (uintptr_t)curlwp;
|
|
MUTEX_ASSERT(mtx, curthread != 0);
|
|
if (MUTEX_ACQUIRE(mtx, curthread)) {
|
|
MUTEX_WANTLOCK(mtx);
|
|
MUTEX_LOCKED(mtx);
|
|
MUTEX_DASSERT(mtx,
|
|
MUTEX_OWNER(mtx->mtx_owner) == curthread);
|
|
return 1;
|
|
}
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
#if defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL)
|
|
/*
|
|
* mutex_spin_retry:
|
|
*
|
|
* Support routine for mutex_spin_enter(). Assumes that the caller
|
|
* has already raised the SPL, and adjusted counters.
|
|
*/
|
|
void
|
|
mutex_spin_retry(kmutex_t *mtx)
|
|
{
|
|
#ifdef MULTIPROCESSOR
|
|
u_int count;
|
|
LOCKSTAT_TIMER(spintime);
|
|
LOCKSTAT_FLAG(lsflag);
|
|
#ifdef LOCKDEBUG
|
|
u_int spins = 0;
|
|
#endif /* LOCKDEBUG */
|
|
|
|
MUTEX_WANTLOCK(mtx);
|
|
|
|
LOCKSTAT_ENTER(lsflag);
|
|
LOCKSTAT_START_TIMER(lsflag, spintime);
|
|
count = SPINLOCK_BACKOFF_MIN;
|
|
|
|
/*
|
|
* Spin testing the lock word and do exponential backoff
|
|
* to reduce cache line ping-ponging between CPUs.
|
|
*/
|
|
do {
|
|
if (panicstr != NULL)
|
|
break;
|
|
while (mtx->mtx_lock == __SIMPLELOCK_LOCKED) {
|
|
SPINLOCK_BACKOFF(count);
|
|
#ifdef LOCKDEBUG
|
|
if (SPINLOCK_SPINOUT(spins))
|
|
MUTEX_ABORT(mtx, "spinout");
|
|
#endif /* LOCKDEBUG */
|
|
}
|
|
} while (!__cpu_simple_lock_try(&mtx->mtx_lock));
|
|
|
|
LOCKSTAT_STOP_TIMER(lsflag, spintime);
|
|
LOCKSTAT_EVENT(lsflag, mtx, LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
|
|
LOCKSTAT_EXIT(lsflag);
|
|
|
|
MUTEX_LOCKED(mtx);
|
|
#else /* MULTIPROCESSOR */
|
|
MUTEX_ABORT(mtx, "locking against myself");
|
|
#endif /* MULTIPROCESSOR */
|
|
}
|
|
#endif /* defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) */
|
|
|
|
/*
|
|
* sched_lock_idle:
|
|
*
|
|
* XXX Ugly hack for cpu_switch().
|
|
*/
|
|
void
|
|
sched_lock_idle(void)
|
|
{
|
|
#ifdef FULL
|
|
kmutex_t *mtx = &sched_mutex;
|
|
|
|
curcpu()->ci_mtx_count--;
|
|
|
|
if (!__cpu_simple_lock_try(&mtx->mtx_lock)) {
|
|
mutex_spin_retry(mtx);
|
|
return;
|
|
}
|
|
|
|
MUTEX_LOCKED(mtx);
|
|
#else
|
|
curcpu()->ci_mtx_count--;
|
|
#endif /* FULL */
|
|
}
|
|
|
|
/*
|
|
* sched_unlock_idle:
|
|
*
|
|
* XXX Ugly hack for cpu_switch().
|
|
*/
|
|
void
|
|
sched_unlock_idle(void)
|
|
{
|
|
#ifdef FULL
|
|
kmutex_t *mtx = &sched_mutex;
|
|
|
|
if (mtx->mtx_lock != __SIMPLELOCK_LOCKED)
|
|
MUTEX_ABORT(mtx, "sched_mutex not locked");
|
|
|
|
MUTEX_UNLOCKED(mtx);
|
|
__cpu_simple_unlock(&mtx->mtx_lock);
|
|
#endif /* FULL */
|
|
curcpu()->ci_mtx_count++;
|
|
}
|