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NetBSD/sys/kern/kern_mutex.c

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/* $NetBSD: kern_mutex.c,v 1.41 2008/05/19 17:06:02 ad Exp $ */
/*-
* Copyright (c) 2002, 2006, 2007, 2008 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.
*
* 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.
*/
#define __MUTEX_PRIVATE
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.41 2008/05/19 17:06:02 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 <sys/atomic.h>
#include <sys/intr.h>
#include <sys/lock.h>
#include <sys/pool.h>
#include <dev/lockstat.h>
#include <machine/lock.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_DEBUG_P(mtx), (mtx), \
(uintptr_t)__builtin_return_address(0), false, false)
#define MUTEX_LOCKED(mtx) \
LOCKDEBUG_LOCKED(MUTEX_DEBUG_P(mtx), (mtx), \
(uintptr_t)__builtin_return_address(0), 0)
#define MUTEX_UNLOCKED(mtx) \
LOCKDEBUG_UNLOCKED(MUTEX_DEBUG_P(mtx), (mtx), \
(uintptr_t)__builtin_return_address(0), 0)
#define MUTEX_ABORT(mtx, msg) \
mutex_abort(mtx, __func__, 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; \
int x__cnt, s; \
s = splraiseipl(mtx->mtx_ipl); \
x__ci = curcpu(); \
x__cnt = x__ci->ci_mtx_count--; \
__insn_barrier(); \
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_HAS_WAITERS(mtx) \
(((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0)
#define MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug) \
do { \
if (dodebug) \
(mtx)->mtx_owner |= MUTEX_BIT_DEBUG; \
} while (/* CONSTCOND */ 0);
#define MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl) \
do { \
(mtx)->mtx_owner = MUTEX_BIT_SPIN; \
if (dodebug) \
(mtx)->mtx_owner |= MUTEX_BIT_DEBUG; \
(mtx)->mtx_ipl = makeiplcookie((ipl)); \
__cpu_simple_lock_init(&(mtx)->mtx_lock); \
} while (/* CONSTCOND */ 0)
#define MUTEX_DESTROY(mtx) \
do { \
(mtx)->mtx_owner = MUTEX_THREAD; \
} 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_DEBUG_P(mtx) (((mtx)->mtx_owner & MUTEX_BIT_DEBUG) != 0)
#if defined(LOCKDEBUG)
#define MUTEX_OWNED(owner) (((owner) & ~MUTEX_BIT_DEBUG) != 0)
#define MUTEX_INHERITDEBUG(new, old) (new) |= (old) & MUTEX_BIT_DEBUG
#else /* defined(LOCKDEBUG) */
#define MUTEX_OWNED(owner) ((owner) != 0)
#define MUTEX_INHERITDEBUG(new, old) /* nothing */
#endif /* defined(LOCKDEBUG) */
static inline int
MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
{
int rv;
uintptr_t old = 0;
uintptr_t new = curthread;
MUTEX_INHERITDEBUG(old, mtx->mtx_owner);
MUTEX_INHERITDEBUG(new, old);
rv = MUTEX_CAS(&mtx->mtx_owner, old, new);
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)
{
uintptr_t new;
MUTEX_GIVE(mtx);
new = 0;
MUTEX_INHERITDEBUG(new, mtx->mtx_owner);
mtx->mtx_owner = new;
}
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 **);
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,
(void *)mutex_owner,
};
/* Mutex cache */
#define MUTEX_OBJ_MAGIC 0x5aa3c85d
struct kmutexobj {
kmutex_t mo_lock;
u_int mo_magic;
u_int mo_refcnt;
};
static int mutex_obj_ctor(void *, void *, int);
static pool_cache_t mutex_obj_cache;
/*
* 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(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)
{
bool dodebug;
memset(mtx, 0, sizeof(*mtx));
switch (type) {
case MUTEX_ADAPTIVE:
KASSERT(ipl == IPL_NONE);
break;
case MUTEX_DEFAULT:
case MUTEX_DRIVER:
if (ipl == IPL_NONE || ipl == IPL_SOFTCLOCK ||
ipl == IPL_SOFTBIO || ipl == IPL_SOFTNET ||
ipl == IPL_SOFTSERIAL) {
type = MUTEX_ADAPTIVE;
} else {
type = MUTEX_SPIN;
}
break;
default:
break;
}
switch (type) {
case MUTEX_NODEBUG:
dodebug = LOCKDEBUG_ALLOC(mtx, NULL,
(uintptr_t)__builtin_return_address(0));
MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
break;
case MUTEX_ADAPTIVE:
dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops,
(uintptr_t)__builtin_return_address(0));
MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug);
break;
case MUTEX_SPIN:
dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops,
(uintptr_t)__builtin_return_address(0));
MUTEX_INITIALIZE_SPIN(mtx, dodebug, 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, !__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock));
}
LOCKDEBUG_FREE(MUTEX_DEBUG_P(mtx), 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
* must release it. This is necessary to avoid deadlock.
*
* 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.
*/
#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);
/* See if the target is running on a CPU somewhere. */
if ((ci = *cip) != NULL && ci->ci_curlwp == l)
goto run;
for (CPU_INFO_FOREACH(cii, ci))
if (ci->ci_curlwp == l)
goto run;
/* No: it may be safe to block now. */
*cip = NULL;
return 0;
run:
/* Target is running; do we need to block? */
*cip = ci;
return ci->ci_biglock_wanted != l;
}
#endif /* MULTIPROCESSOR */
/*
* 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 (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
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);
if (panicstr == NULL) {
LOCKDEBUG_BARRIER(&kernel_lock, 1);
}
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;
owner = mtx->mtx_owner;
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 (;;) {
SPINLOCK_BACKOFF(count);
owner = mtx->mtx_owner;
if (!mutex_onproc(owner, &ci))
break;
}
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);
owner = mtx->mtx_owner;
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 - guaranteed
* 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 mi_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 opportunity 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 ((membar_consumer(), mutex_onproc(owner, &ci)) ||
(membar_consumer(), !MUTEX_HAS_WAITERS(mtx))) {
turnstile_exit(mtx);
owner = mtx->mtx_owner;
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);
owner = mtx->mtx_owner;
}
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 (__predict_false(!__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock))) {
if (panicstr != NULL)
return;
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);
#ifdef LOCKDEBUG
/*
* Avoid having to take the turnstile chain lock every time
* around. Raise the priority level to splhigh() in order
* to disable preemption and so make the following atomic.
*/
{
int s = splhigh();
if (!MUTEX_HAS_WAITERS(mtx)) {
MUTEX_RELEASE(mtx);
splx(s);
return;
}
splx(s);
}
#endif
/*
* 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 (mtx == NULL)
return 0;
if (MUTEX_ADAPTIVE_P(mtx))
return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp;
#ifdef FULL
return __SIMPLELOCK_LOCKED_P(&mtx->mtx_lock);
#else
return 1;
#endif
}
/*
* mutex_owner:
*
* Return the current owner of an adaptive mutex. Used for
* priority inheritance.
*/
lwp_t *
mutex_owner(kmutex_t *mtx)
{
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 (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
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) */
/*
* mutex_obj_init:
*
* Initialize the mutex object store.
*/
void
mutex_obj_init(void)
{
mutex_obj_cache = pool_cache_init(sizeof(struct kmutexobj),
coherency_unit, 0, 0, "mutex", NULL, IPL_NONE, mutex_obj_ctor,
NULL, NULL);
}
/*
* mutex_obj_ctor:
*
* Initialize a new lock for the cache.
*/
static int
mutex_obj_ctor(void *arg, void *obj, int flags)
{
struct kmutexobj * mo = obj;
mo->mo_magic = MUTEX_OBJ_MAGIC;
return 0;
}
/*
* mutex_obj_alloc:
*
* Allocate a single lock object.
*/
kmutex_t *
mutex_obj_alloc(kmutex_type_t type, int ipl)
{
struct kmutexobj *mo;
mo = pool_cache_get(mutex_obj_cache, PR_WAITOK);
mutex_init(&mo->mo_lock, type, ipl);
mo->mo_refcnt = 1;
return (kmutex_t *)mo;
}
/*
* mutex_obj_hold:
*
* Add a single reference to a lock object. A reference to the object
* must already be held, and must be held across this call.
*/
void
mutex_obj_hold(kmutex_t *lock)
{
struct kmutexobj *mo = (struct kmutexobj *)lock;
KASSERT(mo->mo_magic == MUTEX_OBJ_MAGIC);
KASSERT(mo->mo_refcnt > 0);
atomic_inc_uint(&mo->mo_refcnt);
}
/*
* mutex_obj_free:
*
* Drop a reference from a lock object. If the last reference is being
* dropped, free the object and return true. Otherwise, return false.
*/
bool
mutex_obj_free(kmutex_t *lock)
{
struct kmutexobj *mo = (struct kmutexobj *)lock;
KASSERT(mo->mo_magic == MUTEX_OBJ_MAGIC);
KASSERT(mo->mo_refcnt > 0);
if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) {
return false;
}
mutex_destroy(&mo->mo_lock);
pool_cache_put(mutex_obj_cache, mo);
return true;
}
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