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freebsd-nq/sys/kern/kern_lock.c
Ivan Voras 2573ea5f76 Print out process name and thread id in the debugging message. 
This is useful because the message can end up in system logs in
non-debugging operation.

Reviewed by:	attilio (earlier version)
2012-03-05 14:19:43 +00:00

1464 lines
39 KiB
C
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/*-
* Copyright (c) 2008 Attilio Rao <attilio@FreeBSD.org>
* All rights reserved.
*
* 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(s), this list of conditions and the following disclaimer as
* the first lines of this file unmodified other than the possible
* addition of one or more copyright notices.
* 2. Redistributions in binary form must reproduce the above copyright
* notice(s), 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 COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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.
*/
#include "opt_adaptive_lockmgrs.h"
#include "opt_ddb.h"
#include "opt_kdtrace.h"
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/lock_profile.h>
#include <sys/lockmgr.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sleepqueue.h>
#ifdef DEBUG_LOCKS
#include <sys/stack.h>
#endif
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <machine/cpu.h>
#ifdef DDB
#include <ddb/ddb.h>
#endif
CTASSERT(((LK_ADAPTIVE | LK_NOSHARE) & LO_CLASSFLAGS) ==
(LK_ADAPTIVE | LK_NOSHARE));
CTASSERT(LK_UNLOCKED == (LK_UNLOCKED &
~(LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS)));
#define SQ_EXCLUSIVE_QUEUE 0
#define SQ_SHARED_QUEUE 1
#ifndef INVARIANTS
#define _lockmgr_assert(lk, what, file, line)
#define TD_LOCKS_INC(td)
#define TD_LOCKS_DEC(td)
#else
#define TD_LOCKS_INC(td) ((td)->td_locks++)
#define TD_LOCKS_DEC(td) ((td)->td_locks--)
#endif
#define TD_SLOCKS_INC(td) ((td)->td_lk_slocks++)
#define TD_SLOCKS_DEC(td) ((td)->td_lk_slocks--)
#ifndef DEBUG_LOCKS
#define STACK_PRINT(lk)
#define STACK_SAVE(lk)
#define STACK_ZERO(lk)
#else
#define STACK_PRINT(lk) stack_print_ddb(&(lk)->lk_stack)
#define STACK_SAVE(lk) stack_save(&(lk)->lk_stack)
#define STACK_ZERO(lk) stack_zero(&(lk)->lk_stack)
#endif
#define LOCK_LOG2(lk, string, arg1, arg2) \
if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \
CTR2(KTR_LOCK, (string), (arg1), (arg2))
#define LOCK_LOG3(lk, string, arg1, arg2, arg3) \
if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \
CTR3(KTR_LOCK, (string), (arg1), (arg2), (arg3))
#define GIANT_DECLARE \
int _i = 0; \
WITNESS_SAVE_DECL(Giant)
#define GIANT_RESTORE() do { \
if (_i > 0) { \
while (_i--) \
mtx_lock(&Giant); \
WITNESS_RESTORE(&Giant.lock_object, Giant); \
} \
} while (0)
#define GIANT_SAVE() do { \
if (mtx_owned(&Giant)) { \
WITNESS_SAVE(&Giant.lock_object, Giant); \
while (mtx_owned(&Giant)) { \
_i++; \
mtx_unlock(&Giant); \
} \
} \
} while (0)
#define LK_CAN_SHARE(x) \
(((x) & LK_SHARE) && (((x) & LK_EXCLUSIVE_WAITERS) == 0 || \
((x) & LK_EXCLUSIVE_SPINNERS) == 0 || \
curthread->td_lk_slocks || (curthread->td_pflags & TDP_DEADLKTREAT)))
#define LK_TRYOP(x) \
((x) & LK_NOWAIT)
#define LK_CAN_WITNESS(x) \
(((x) & LK_NOWITNESS) == 0 && !LK_TRYOP(x))
#define LK_TRYWIT(x) \
(LK_TRYOP(x) ? LOP_TRYLOCK : 0)
#define LK_CAN_ADAPT(lk, f) \
(((lk)->lock_object.lo_flags & LK_ADAPTIVE) != 0 && \
((f) & LK_SLEEPFAIL) == 0)
#define lockmgr_disowned(lk) \
(((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == LK_KERNPROC)
#define lockmgr_xlocked(lk) \
(((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == (uintptr_t)curthread)
static void assert_lockmgr(const struct lock_object *lock, int how);
#ifdef DDB
static void db_show_lockmgr(const struct lock_object *lock);
#endif
static void lock_lockmgr(struct lock_object *lock, int how);
#ifdef KDTRACE_HOOKS
static int owner_lockmgr(const struct lock_object *lock,
struct thread **owner);
#endif
static int unlock_lockmgr(struct lock_object *lock);
struct lock_class lock_class_lockmgr = {
.lc_name = "lockmgr",
.lc_flags = LC_RECURSABLE | LC_SLEEPABLE | LC_SLEEPLOCK | LC_UPGRADABLE,
.lc_assert = assert_lockmgr,
#ifdef DDB
.lc_ddb_show = db_show_lockmgr,
#endif
.lc_lock = lock_lockmgr,
.lc_unlock = unlock_lockmgr,
#ifdef KDTRACE_HOOKS
.lc_owner = owner_lockmgr,
#endif
};
#ifdef ADAPTIVE_LOCKMGRS
static u_int alk_retries = 10;
static u_int alk_loops = 10000;
static SYSCTL_NODE(_debug, OID_AUTO, lockmgr, CTLFLAG_RD, NULL,
"lockmgr debugging");
SYSCTL_UINT(_debug_lockmgr, OID_AUTO, retries, CTLFLAG_RW, &alk_retries, 0, "");
SYSCTL_UINT(_debug_lockmgr, OID_AUTO, loops, CTLFLAG_RW, &alk_loops, 0, "");
#endif
static __inline struct thread *
lockmgr_xholder(const struct lock *lk)
{
uintptr_t x;
x = lk->lk_lock;
return ((x & LK_SHARE) ? NULL : (struct thread *)LK_HOLDER(x));
}
/*
* It assumes sleepq_lock held and returns with this one unheld.
* It also assumes the generic interlock is sane and previously checked.
* If LK_INTERLOCK is specified the interlock is not reacquired after the
* sleep.
*/
static __inline int
sleeplk(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *wmesg, int pri, int timo, int queue)
{
GIANT_DECLARE;
struct lock_class *class;
int catch, error;
class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
catch = pri & PCATCH;
pri &= PRIMASK;
error = 0;
LOCK_LOG3(lk, "%s: %p blocking on the %s sleepqueue", __func__, lk,
(queue == SQ_EXCLUSIVE_QUEUE) ? "exclusive" : "shared");
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
if (queue == SQ_EXCLUSIVE_QUEUE && (flags & LK_SLEEPFAIL) != 0)
lk->lk_exslpfail++;
GIANT_SAVE();
sleepq_add(&lk->lock_object, NULL, wmesg, SLEEPQ_LK | (catch ?
SLEEPQ_INTERRUPTIBLE : 0), queue);
if ((flags & LK_TIMELOCK) && timo)
sleepq_set_timeout(&lk->lock_object, timo);
/*
* Decisional switch for real sleeping.
*/
if ((flags & LK_TIMELOCK) && timo && catch)
error = sleepq_timedwait_sig(&lk->lock_object, pri);
else if ((flags & LK_TIMELOCK) && timo)
error = sleepq_timedwait(&lk->lock_object, pri);
else if (catch)
error = sleepq_wait_sig(&lk->lock_object, pri);
else
sleepq_wait(&lk->lock_object, pri);
GIANT_RESTORE();
if ((flags & LK_SLEEPFAIL) && error == 0)
error = ENOLCK;
return (error);
}
static __inline int
wakeupshlk(struct lock *lk, const char *file, int line)
{
uintptr_t v, x;
u_int realexslp;
int queue, wakeup_swapper;
TD_LOCKS_DEC(curthread);
TD_SLOCKS_DEC(curthread);
WITNESS_UNLOCK(&lk->lock_object, 0, file, line);
LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, file, line);
wakeup_swapper = 0;
for (;;) {
x = lk->lk_lock;
/*
* If there is more than one shared lock held, just drop one
* and return.
*/
if (LK_SHARERS(x) > 1) {
if (atomic_cmpset_rel_ptr(&lk->lk_lock, x,
x - LK_ONE_SHARER))
break;
continue;
}
/*
* If there are not waiters on the exclusive queue, drop the
* lock quickly.
*/
if ((x & LK_ALL_WAITERS) == 0) {
MPASS((x & ~LK_EXCLUSIVE_SPINNERS) ==
LK_SHARERS_LOCK(1));
if (atomic_cmpset_rel_ptr(&lk->lk_lock, x, LK_UNLOCKED))
break;
continue;
}
/*
* We should have a sharer with waiters, so enter the hard
* path in order to handle wakeups correctly.
*/
sleepq_lock(&lk->lock_object);
x = lk->lk_lock & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
v = LK_UNLOCKED;
/*
* If the lock has exclusive waiters, give them preference in
* order to avoid deadlock with shared runners up.
* If interruptible sleeps left the exclusive queue empty
* avoid a starvation for the threads sleeping on the shared
* queue by giving them precedence and cleaning up the
* exclusive waiters bit anyway.
* Please note that lk_exslpfail count may be lying about
* the real number of waiters with the LK_SLEEPFAIL flag on
* because they may be used in conjuction with interruptible
* sleeps so lk_exslpfail might be considered an 'upper limit'
* bound, including the edge cases.
*/
realexslp = sleepq_sleepcnt(&lk->lock_object,
SQ_EXCLUSIVE_QUEUE);
if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) {
if (lk->lk_exslpfail < realexslp) {
lk->lk_exslpfail = 0;
queue = SQ_EXCLUSIVE_QUEUE;
v |= (x & LK_SHARED_WAITERS);
} else {
lk->lk_exslpfail = 0;
LOCK_LOG2(lk,
"%s: %p has only LK_SLEEPFAIL sleepers",
__func__, lk);
LOCK_LOG2(lk,
"%s: %p waking up threads on the exclusive queue",
__func__, lk);
wakeup_swapper =
sleepq_broadcast(&lk->lock_object,
SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE);
queue = SQ_SHARED_QUEUE;
}
} else {
/*
* Exclusive waiters sleeping with LK_SLEEPFAIL on
* and using interruptible sleeps/timeout may have
* left spourious lk_exslpfail counts on, so clean
* it up anyway.
*/
lk->lk_exslpfail = 0;
queue = SQ_SHARED_QUEUE;
}
if (!atomic_cmpset_rel_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x,
v)) {
sleepq_release(&lk->lock_object);
continue;
}
LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue",
__func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
"exclusive");
wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK,
0, queue);
sleepq_release(&lk->lock_object);
break;
}
lock_profile_release_lock(&lk->lock_object);
return (wakeup_swapper);
}
static void
assert_lockmgr(const struct lock_object *lock, int what)
{
panic("lockmgr locks do not support assertions");
}
static void
lock_lockmgr(struct lock_object *lock, int how)
{
panic("lockmgr locks do not support sleep interlocking");
}
static int
unlock_lockmgr(struct lock_object *lock)
{
panic("lockmgr locks do not support sleep interlocking");
}
#ifdef KDTRACE_HOOKS
static int
owner_lockmgr(const struct lock_object *lock, struct thread **owner)
{
panic("lockmgr locks do not support owner inquiring");
}
#endif
void
lockinit(struct lock *lk, int pri, const char *wmesg, int timo, int flags)
{
int iflags;
MPASS((flags & ~LK_INIT_MASK) == 0);
ASSERT_ATOMIC_LOAD_PTR(lk->lk_lock,
("%s: lockmgr not aligned for %s: %p", __func__, wmesg,
&lk->lk_lock));
iflags = LO_SLEEPABLE | LO_UPGRADABLE;
if (flags & LK_CANRECURSE)
iflags |= LO_RECURSABLE;
if ((flags & LK_NODUP) == 0)
iflags |= LO_DUPOK;
if (flags & LK_NOPROFILE)
iflags |= LO_NOPROFILE;
if ((flags & LK_NOWITNESS) == 0)
iflags |= LO_WITNESS;
if (flags & LK_QUIET)
iflags |= LO_QUIET;
iflags |= flags & (LK_ADAPTIVE | LK_NOSHARE);
lk->lk_lock = LK_UNLOCKED;
lk->lk_recurse = 0;
lk->lk_exslpfail = 0;
lk->lk_timo = timo;
lk->lk_pri = pri;
lock_init(&lk->lock_object, &lock_class_lockmgr, wmesg, NULL, iflags);
STACK_ZERO(lk);
}
/*
* XXX: Gross hacks to manipulate external lock flags after
* initialization. Used for certain vnode and buf locks.
*/
void
lockallowshare(struct lock *lk)
{
lockmgr_assert(lk, KA_XLOCKED);
lk->lock_object.lo_flags &= ~LK_NOSHARE;
}
void
lockallowrecurse(struct lock *lk)
{
lockmgr_assert(lk, KA_XLOCKED);
lk->lock_object.lo_flags |= LO_RECURSABLE;
}
void
lockdisablerecurse(struct lock *lk)
{
lockmgr_assert(lk, KA_XLOCKED);
lk->lock_object.lo_flags &= ~LO_RECURSABLE;
}
void
lockdestroy(struct lock *lk)
{
KASSERT(lk->lk_lock == LK_UNLOCKED, ("lockmgr still held"));
KASSERT(lk->lk_recurse == 0, ("lockmgr still recursed"));
KASSERT(lk->lk_exslpfail == 0, ("lockmgr still exclusive waiters"));
lock_destroy(&lk->lock_object);
}
int
__lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *wmesg, int pri, int timo, const char *file, int line)
{
GIANT_DECLARE;
struct lock_class *class;
const char *iwmesg;
uintptr_t tid, v, x;
u_int op, realexslp;
int error, ipri, itimo, queue, wakeup_swapper;
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
int contested = 0;
#endif
#ifdef ADAPTIVE_LOCKMGRS
volatile struct thread *owner;
u_int i, spintries = 0;
#endif
error = 0;
tid = (uintptr_t)curthread;
op = (flags & LK_TYPE_MASK);
iwmesg = (wmesg == LK_WMESG_DEFAULT) ? lk->lock_object.lo_name : wmesg;
ipri = (pri == LK_PRIO_DEFAULT) ? lk->lk_pri : pri;
itimo = (timo == LK_TIMO_DEFAULT) ? lk->lk_timo : timo;
MPASS((flags & ~LK_TOTAL_MASK) == 0);
KASSERT((op & (op - 1)) == 0,
("%s: Invalid requested operation @ %s:%d", __func__, file, line));
KASSERT((flags & (LK_NOWAIT | LK_SLEEPFAIL)) == 0 ||
(op != LK_DOWNGRADE && op != LK_RELEASE),
("%s: Invalid flags in regard of the operation desired @ %s:%d",
__func__, file, line));
KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL,
("%s: LK_INTERLOCK passed without valid interlock @ %s:%d",
__func__, file, line));
class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
if (panicstr != NULL) {
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
return (0);
}
if (lk->lock_object.lo_flags & LK_NOSHARE) {
switch (op) {
case LK_SHARED:
op = LK_EXCLUSIVE;
break;
case LK_UPGRADE:
case LK_DOWNGRADE:
_lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED,
file, line);
return (0);
}
}
wakeup_swapper = 0;
switch (op) {
case LK_SHARED:
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
file, line, ilk);
for (;;) {
x = lk->lk_lock;
/*
* If no other thread has an exclusive lock, or
* no exclusive waiter is present, bump the count of
* sharers. Since we have to preserve the state of
* waiters, if we fail to acquire the shared lock
* loop back and retry.
*/
if (LK_CAN_SHARE(x)) {
if (atomic_cmpset_acq_ptr(&lk->lk_lock, x,
x + LK_ONE_SHARER))
break;
continue;
}
lock_profile_obtain_lock_failed(&lk->lock_object,
&contested, &waittime);
/*
* If the lock is already held by curthread in
* exclusive way avoid a deadlock.
*/
if (LK_HOLDER(x) == tid) {
LOCK_LOG2(lk,
"%s: %p already held in exclusive mode",
__func__, lk);
error = EDEADLK;
break;
}
/*
* If the lock is expected to not sleep just give up
* and return.
*/
if (LK_TRYOP(flags)) {
LOCK_LOG2(lk, "%s: %p fails the try operation",
__func__, lk);
error = EBUSY;
break;
}
#ifdef ADAPTIVE_LOCKMGRS
/*
* If the owner is running on another CPU, spin until
* the owner stops running or the state of the lock
* changes. We need a double-state handle here
* because for a failed acquisition the lock can be
* either held in exclusive mode or shared mode
* (for the writer starvation avoidance technique).
*/
if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 &&
LK_HOLDER(x) != LK_KERNPROC) {
owner = (struct thread *)LK_HOLDER(x);
if (LOCK_LOG_TEST(&lk->lock_object, 0))
CTR3(KTR_LOCK,
"%s: spinning on %p held by %p",
__func__, lk, owner);
/*
* If we are holding also an interlock drop it
* in order to avoid a deadlock if the lockmgr
* owner is adaptively spinning on the
* interlock itself.
*/
if (flags & LK_INTERLOCK) {
class->lc_unlock(ilk);
flags &= ~LK_INTERLOCK;
}
GIANT_SAVE();
while (LK_HOLDER(lk->lk_lock) ==
(uintptr_t)owner && TD_IS_RUNNING(owner))
cpu_spinwait();
GIANT_RESTORE();
continue;
} else if (LK_CAN_ADAPT(lk, flags) &&
(x & LK_SHARE) != 0 && LK_SHARERS(x) &&
spintries < alk_retries) {
if (flags & LK_INTERLOCK) {
class->lc_unlock(ilk);
flags &= ~LK_INTERLOCK;
}
GIANT_SAVE();
spintries++;
for (i = 0; i < alk_loops; i++) {
if (LOCK_LOG_TEST(&lk->lock_object, 0))
CTR4(KTR_LOCK,
"%s: shared spinning on %p with %u and %u",
__func__, lk, spintries, i);
x = lk->lk_lock;
if ((x & LK_SHARE) == 0 ||
LK_CAN_SHARE(x) != 0)
break;
cpu_spinwait();
}
GIANT_RESTORE();
if (i != alk_loops)
continue;
}
#endif
/*
* Acquire the sleepqueue chain lock because we
* probabilly will need to manipulate waiters flags.
*/
sleepq_lock(&lk->lock_object);
x = lk->lk_lock;
/*
* if the lock can be acquired in shared mode, try
* again.
*/
if (LK_CAN_SHARE(x)) {
sleepq_release(&lk->lock_object);
continue;
}
#ifdef ADAPTIVE_LOCKMGRS
/*
* The current lock owner might have started executing
* on another CPU (or the lock could have changed
* owner) while we were waiting on the turnstile
* chain lock. If so, drop the turnstile lock and try
* again.
*/
if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 &&
LK_HOLDER(x) != LK_KERNPROC) {
owner = (struct thread *)LK_HOLDER(x);
if (TD_IS_RUNNING(owner)) {
sleepq_release(&lk->lock_object);
continue;
}
}
#endif
/*
* Try to set the LK_SHARED_WAITERS flag. If we fail,
* loop back and retry.
*/
if ((x & LK_SHARED_WAITERS) == 0) {
if (!atomic_cmpset_acq_ptr(&lk->lk_lock, x,
x | LK_SHARED_WAITERS)) {
sleepq_release(&lk->lock_object);
continue;
}
LOCK_LOG2(lk, "%s: %p set shared waiters flag",
__func__, lk);
}
/*
* As far as we have been unable to acquire the
* shared lock and the shared waiters flag is set,
* we will sleep.
*/
error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
SQ_SHARED_QUEUE);
flags &= ~LK_INTERLOCK;
if (error) {
LOCK_LOG3(lk,
"%s: interrupted sleep for %p with %d",
__func__, lk, error);
break;
}
LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
__func__, lk);
}
if (error == 0) {
lock_profile_obtain_lock_success(&lk->lock_object,
contested, waittime, file, line);
LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, file,
line);
WITNESS_LOCK(&lk->lock_object, LK_TRYWIT(flags), file,
line);
TD_LOCKS_INC(curthread);
TD_SLOCKS_INC(curthread);
STACK_SAVE(lk);
}
break;
case LK_UPGRADE:
_lockmgr_assert(lk, KA_SLOCKED, file, line);
v = lk->lk_lock;
x = v & LK_ALL_WAITERS;
v &= LK_EXCLUSIVE_SPINNERS;
/*
* Try to switch from one shared lock to an exclusive one.
* We need to preserve waiters flags during the operation.
*/
if (atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x | v,
tid | x)) {
LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file,
line);
WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
TD_SLOCKS_DEC(curthread);
break;
}
/*
* We have been unable to succeed in upgrading, so just
* give up the shared lock.
*/
wakeup_swapper |= wakeupshlk(lk, file, line);
/* FALLTHROUGH */
case LK_EXCLUSIVE:
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
LOP_EXCLUSIVE, file, line, ilk);
/*
* If curthread already holds the lock and this one is
* allowed to recurse, simply recurse on it.
*/
if (lockmgr_xlocked(lk)) {
if ((flags & LK_CANRECURSE) == 0 &&
(lk->lock_object.lo_flags & LO_RECURSABLE) == 0) {
/*
* If the lock is expected to not panic just
* give up and return.
*/
if (LK_TRYOP(flags)) {
LOCK_LOG2(lk,
"%s: %p fails the try operation",
__func__, lk);
error = EBUSY;
break;
}
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
panic("%s: recursing on non recursive lockmgr %s @ %s:%d\n",
__func__, iwmesg, file, line);
}
lk->lk_recurse++;
LOCK_LOG2(lk, "%s: %p recursing", __func__, lk);
LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0,
lk->lk_recurse, file, line);
WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
TD_LOCKS_INC(curthread);
break;
}
while (!atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED,
tid)) {
lock_profile_obtain_lock_failed(&lk->lock_object,
&contested, &waittime);
/*
* If the lock is expected to not sleep just give up
* and return.
*/
if (LK_TRYOP(flags)) {
LOCK_LOG2(lk, "%s: %p fails the try operation",
__func__, lk);
error = EBUSY;
break;
}
#ifdef ADAPTIVE_LOCKMGRS
/*
* If the owner is running on another CPU, spin until
* the owner stops running or the state of the lock
* changes.
*/
x = lk->lk_lock;
if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 &&
LK_HOLDER(x) != LK_KERNPROC) {
owner = (struct thread *)LK_HOLDER(x);
if (LOCK_LOG_TEST(&lk->lock_object, 0))
CTR3(KTR_LOCK,
"%s: spinning on %p held by %p",
__func__, lk, owner);
/*
* If we are holding also an interlock drop it
* in order to avoid a deadlock if the lockmgr
* owner is adaptively spinning on the
* interlock itself.
*/
if (flags & LK_INTERLOCK) {
class->lc_unlock(ilk);
flags &= ~LK_INTERLOCK;
}
GIANT_SAVE();
while (LK_HOLDER(lk->lk_lock) ==
(uintptr_t)owner && TD_IS_RUNNING(owner))
cpu_spinwait();
GIANT_RESTORE();
continue;
} else if (LK_CAN_ADAPT(lk, flags) &&
(x & LK_SHARE) != 0 && LK_SHARERS(x) &&
spintries < alk_retries) {
if ((x & LK_EXCLUSIVE_SPINNERS) == 0 &&
!atomic_cmpset_ptr(&lk->lk_lock, x,
x | LK_EXCLUSIVE_SPINNERS))
continue;
if (flags & LK_INTERLOCK) {
class->lc_unlock(ilk);
flags &= ~LK_INTERLOCK;
}
GIANT_SAVE();
spintries++;
for (i = 0; i < alk_loops; i++) {
if (LOCK_LOG_TEST(&lk->lock_object, 0))
CTR4(KTR_LOCK,
"%s: shared spinning on %p with %u and %u",
__func__, lk, spintries, i);
if ((lk->lk_lock &
LK_EXCLUSIVE_SPINNERS) == 0)
break;
cpu_spinwait();
}
GIANT_RESTORE();
if (i != alk_loops)
continue;
}
#endif
/*
* Acquire the sleepqueue chain lock because we
* probabilly will need to manipulate waiters flags.
*/
sleepq_lock(&lk->lock_object);
x = lk->lk_lock;
/*
* if the lock has been released while we spun on
* the sleepqueue chain lock just try again.
*/
if (x == LK_UNLOCKED) {
sleepq_release(&lk->lock_object);
continue;
}
#ifdef ADAPTIVE_LOCKMGRS
/*
* The current lock owner might have started executing
* on another CPU (or the lock could have changed
* owner) while we were waiting on the turnstile
* chain lock. If so, drop the turnstile lock and try
* again.
*/
if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 &&
LK_HOLDER(x) != LK_KERNPROC) {
owner = (struct thread *)LK_HOLDER(x);
if (TD_IS_RUNNING(owner)) {
sleepq_release(&lk->lock_object);
continue;
}
}
#endif
/*
* The lock can be in the state where there is a
* pending queue of waiters, but still no owner.
* This happens when the lock is contested and an
* owner is going to claim the lock.
* If curthread is the one successfully acquiring it
* claim lock ownership and return, preserving waiters
* flags.
*/
v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
if ((x & ~v) == LK_UNLOCKED) {
v &= ~LK_EXCLUSIVE_SPINNERS;
if (atomic_cmpset_acq_ptr(&lk->lk_lock, x,
tid | v)) {
sleepq_release(&lk->lock_object);
LOCK_LOG2(lk,
"%s: %p claimed by a new writer",
__func__, lk);
break;
}
sleepq_release(&lk->lock_object);
continue;
}
/*
* Try to set the LK_EXCLUSIVE_WAITERS flag. If we
* fail, loop back and retry.
*/
if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
if (!atomic_cmpset_ptr(&lk->lk_lock, x,
x | LK_EXCLUSIVE_WAITERS)) {
sleepq_release(&lk->lock_object);
continue;
}
LOCK_LOG2(lk, "%s: %p set excl waiters flag",
__func__, lk);
}
/*
* As far as we have been unable to acquire the
* exclusive lock and the exclusive waiters flag
* is set, we will sleep.
*/
error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
SQ_EXCLUSIVE_QUEUE);
flags &= ~LK_INTERLOCK;
if (error) {
LOCK_LOG3(lk,
"%s: interrupted sleep for %p with %d",
__func__, lk, error);
break;
}
LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
__func__, lk);
}
if (error == 0) {
lock_profile_obtain_lock_success(&lk->lock_object,
contested, waittime, file, line);
LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0,
lk->lk_recurse, file, line);
WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
TD_LOCKS_INC(curthread);
STACK_SAVE(lk);
}
break;
case LK_DOWNGRADE:
_lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, file, line);
LOCK_LOG_LOCK("XDOWNGRADE", &lk->lock_object, 0, 0, file, line);
WITNESS_DOWNGRADE(&lk->lock_object, 0, file, line);
TD_SLOCKS_INC(curthread);
/*
* In order to preserve waiters flags, just spin.
*/
for (;;) {
x = lk->lk_lock;
MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
x &= LK_ALL_WAITERS;
if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
LK_SHARERS_LOCK(1) | x))
break;
cpu_spinwait();
}
break;
case LK_RELEASE:
_lockmgr_assert(lk, KA_LOCKED, file, line);
x = lk->lk_lock;
if ((x & LK_SHARE) == 0) {
/*
* As first option, treact the lock as if it has not
* any waiter.
* Fix-up the tid var if the lock has been disowned.
*/
if (LK_HOLDER(x) == LK_KERNPROC)
tid = LK_KERNPROC;
else {
WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE,
file, line);
TD_LOCKS_DEC(curthread);
}
LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0,
lk->lk_recurse, file, line);
/*
* The lock is held in exclusive mode.
* If the lock is recursed also, then unrecurse it.
*/
if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) {
LOCK_LOG2(lk, "%s: %p unrecursing", __func__,
lk);
lk->lk_recurse--;
break;
}
if (tid != LK_KERNPROC)
lock_profile_release_lock(&lk->lock_object);
if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid,
LK_UNLOCKED))
break;
sleepq_lock(&lk->lock_object);
x = lk->lk_lock;
v = LK_UNLOCKED;
/*
* If the lock has exclusive waiters, give them
* preference in order to avoid deadlock with
* shared runners up.
* If interruptible sleeps left the exclusive queue
* empty avoid a starvation for the threads sleeping
* on the shared queue by giving them precedence
* and cleaning up the exclusive waiters bit anyway.
* Please note that lk_exslpfail count may be lying
* about the real number of waiters with the
* LK_SLEEPFAIL flag on because they may be used in
* conjuction with interruptible sleeps so
* lk_exslpfail might be considered an 'upper limit'
* bound, including the edge cases.
*/
MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
realexslp = sleepq_sleepcnt(&lk->lock_object,
SQ_EXCLUSIVE_QUEUE);
if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) {
if (lk->lk_exslpfail < realexslp) {
lk->lk_exslpfail = 0;
queue = SQ_EXCLUSIVE_QUEUE;
v |= (x & LK_SHARED_WAITERS);
} else {
lk->lk_exslpfail = 0;
LOCK_LOG2(lk,
"%s: %p has only LK_SLEEPFAIL sleepers",
__func__, lk);
LOCK_LOG2(lk,
"%s: %p waking up threads on the exclusive queue",
__func__, lk);
wakeup_swapper =
sleepq_broadcast(&lk->lock_object,
SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE);
queue = SQ_SHARED_QUEUE;
}
} else {
/*
* Exclusive waiters sleeping with LK_SLEEPFAIL
* on and using interruptible sleeps/timeout
* may have left spourious lk_exslpfail counts
* on, so clean it up anyway.
*/
lk->lk_exslpfail = 0;
queue = SQ_SHARED_QUEUE;
}
LOCK_LOG3(lk,
"%s: %p waking up threads on the %s queue",
__func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
"exclusive");
atomic_store_rel_ptr(&lk->lk_lock, v);
wakeup_swapper |= sleepq_broadcast(&lk->lock_object,
SLEEPQ_LK, 0, queue);
sleepq_release(&lk->lock_object);
break;
} else
wakeup_swapper = wakeupshlk(lk, file, line);
break;
case LK_DRAIN:
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
LOP_EXCLUSIVE, file, line, ilk);
/*
* Trying to drain a lock we already own will result in a
* deadlock.
*/
if (lockmgr_xlocked(lk)) {
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
panic("%s: draining %s with the lock held @ %s:%d\n",
__func__, iwmesg, file, line);
}
while (!atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
lock_profile_obtain_lock_failed(&lk->lock_object,
&contested, &waittime);
/*
* If the lock is expected to not sleep just give up
* and return.
*/
if (LK_TRYOP(flags)) {
LOCK_LOG2(lk, "%s: %p fails the try operation",
__func__, lk);
error = EBUSY;
break;
}
/*
* Acquire the sleepqueue chain lock because we
* probabilly will need to manipulate waiters flags.
*/
sleepq_lock(&lk->lock_object);
x = lk->lk_lock;
/*
* if the lock has been released while we spun on
* the sleepqueue chain lock just try again.
*/
if (x == LK_UNLOCKED) {
sleepq_release(&lk->lock_object);
continue;
}
v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
if ((x & ~v) == LK_UNLOCKED) {
v = (x & ~LK_EXCLUSIVE_SPINNERS);
/*
* If interruptible sleeps left the exclusive
* queue empty avoid a starvation for the
* threads sleeping on the shared queue by
* giving them precedence and cleaning up the
* exclusive waiters bit anyway.
* Please note that lk_exslpfail count may be
* lying about the real number of waiters with
* the LK_SLEEPFAIL flag on because they may
* be used in conjuction with interruptible
* sleeps so lk_exslpfail might be considered
* an 'upper limit' bound, including the edge
* cases.
*/
if (v & LK_EXCLUSIVE_WAITERS) {
queue = SQ_EXCLUSIVE_QUEUE;
v &= ~LK_EXCLUSIVE_WAITERS;
} else {
/*
* Exclusive waiters sleeping with
* LK_SLEEPFAIL on and using
* interruptible sleeps/timeout may
* have left spourious lk_exslpfail
* counts on, so clean it up anyway.
*/
MPASS(v & LK_SHARED_WAITERS);
lk->lk_exslpfail = 0;
queue = SQ_SHARED_QUEUE;
v &= ~LK_SHARED_WAITERS;
}
if (queue == SQ_EXCLUSIVE_QUEUE) {
realexslp =
sleepq_sleepcnt(&lk->lock_object,
SQ_EXCLUSIVE_QUEUE);
if (lk->lk_exslpfail >= realexslp) {
lk->lk_exslpfail = 0;
queue = SQ_SHARED_QUEUE;
v &= ~LK_SHARED_WAITERS;
if (realexslp != 0) {
LOCK_LOG2(lk,
"%s: %p has only LK_SLEEPFAIL sleepers",
__func__, lk);
LOCK_LOG2(lk,
"%s: %p waking up threads on the exclusive queue",
__func__, lk);
wakeup_swapper =
sleepq_broadcast(
&lk->lock_object,
SLEEPQ_LK, 0,
SQ_EXCLUSIVE_QUEUE);
}
} else
lk->lk_exslpfail = 0;
}
if (!atomic_cmpset_ptr(&lk->lk_lock, x, v)) {
sleepq_release(&lk->lock_object);
continue;
}
LOCK_LOG3(lk,
"%s: %p waking up all threads on the %s queue",
__func__, lk, queue == SQ_SHARED_QUEUE ?
"shared" : "exclusive");
wakeup_swapper |= sleepq_broadcast(
&lk->lock_object, SLEEPQ_LK, 0, queue);
/*
* If shared waiters have been woken up we need
* to wait for one of them to acquire the lock
* before to set the exclusive waiters in
* order to avoid a deadlock.
*/
if (queue == SQ_SHARED_QUEUE) {
for (v = lk->lk_lock;
(v & LK_SHARE) && !LK_SHARERS(v);
v = lk->lk_lock)
cpu_spinwait();
}
}
/*
* Try to set the LK_EXCLUSIVE_WAITERS flag. If we
* fail, loop back and retry.
*/
if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
if (!atomic_cmpset_ptr(&lk->lk_lock, x,
x | LK_EXCLUSIVE_WAITERS)) {
sleepq_release(&lk->lock_object);
continue;
}
LOCK_LOG2(lk, "%s: %p set drain waiters flag",
__func__, lk);
}
/*
* As far as we have been unable to acquire the
* exclusive lock and the exclusive waiters flag
* is set, we will sleep.
*/
if (flags & LK_INTERLOCK) {
class->lc_unlock(ilk);
flags &= ~LK_INTERLOCK;
}
GIANT_SAVE();
sleepq_add(&lk->lock_object, NULL, iwmesg, SLEEPQ_LK,
SQ_EXCLUSIVE_QUEUE);
sleepq_wait(&lk->lock_object, ipri & PRIMASK);
GIANT_RESTORE();
LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
__func__, lk);
}
if (error == 0) {
lock_profile_obtain_lock_success(&lk->lock_object,
contested, waittime, file, line);
LOCK_LOG_LOCK("DRAIN", &lk->lock_object, 0,
lk->lk_recurse, file, line);
WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
TD_LOCKS_INC(curthread);
STACK_SAVE(lk);
}
break;
default:
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
panic("%s: unknown lockmgr request 0x%x\n", __func__, op);
}
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
if (wakeup_swapper)
kick_proc0();
return (error);
}
void
_lockmgr_disown(struct lock *lk, const char *file, int line)
{
uintptr_t tid, x;
if (SCHEDULER_STOPPED())
return;
tid = (uintptr_t)curthread;
_lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, file, line);
/*
* If the owner is already LK_KERNPROC just skip the whole operation.
*/
if (LK_HOLDER(lk->lk_lock) != tid)
return;
lock_profile_release_lock(&lk->lock_object);
LOCK_LOG_LOCK("XDISOWN", &lk->lock_object, 0, 0, file, line);
WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line);
TD_LOCKS_DEC(curthread);
STACK_SAVE(lk);
/*
* In order to preserve waiters flags, just spin.
*/
for (;;) {
x = lk->lk_lock;
MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
x &= LK_ALL_WAITERS;
if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
LK_KERNPROC | x))
return;
cpu_spinwait();
}
}
void
lockmgr_printinfo(const struct lock *lk)
{
struct thread *td;
uintptr_t x;
if (lk->lk_lock == LK_UNLOCKED)
printf("lock type %s: UNLOCKED\n", lk->lock_object.lo_name);
else if (lk->lk_lock & LK_SHARE)
printf("lock type %s: SHARED (count %ju)\n",
lk->lock_object.lo_name,
(uintmax_t)LK_SHARERS(lk->lk_lock));
else {
td = lockmgr_xholder(lk);
printf("lock type %s: EXCL by thread %p "
"(pid %d, %s, tid %d)\n", lk->lock_object.lo_name, td,
td->td_proc->p_pid, td->td_proc->p_comm, td->td_tid);
}
x = lk->lk_lock;
if (x & LK_EXCLUSIVE_WAITERS)
printf(" with exclusive waiters pending\n");
if (x & LK_SHARED_WAITERS)
printf(" with shared waiters pending\n");
if (x & LK_EXCLUSIVE_SPINNERS)
printf(" with exclusive spinners pending\n");
STACK_PRINT(lk);
}
int
lockstatus(const struct lock *lk)
{
uintptr_t v, x;
int ret;
ret = LK_SHARED;
x = lk->lk_lock;
v = LK_HOLDER(x);
if ((x & LK_SHARE) == 0) {
if (v == (uintptr_t)curthread || v == LK_KERNPROC)
ret = LK_EXCLUSIVE;
else
ret = LK_EXCLOTHER;
} else if (x == LK_UNLOCKED)
ret = 0;
return (ret);
}
#ifdef INVARIANT_SUPPORT
FEATURE(invariant_support,
"Support for modules compiled with INVARIANTS option");
#ifndef INVARIANTS
#undef _lockmgr_assert
#endif
void
_lockmgr_assert(const struct lock *lk, int what, const char *file, int line)
{
int slocked = 0;
if (panicstr != NULL)
return;
switch (what) {
case KA_SLOCKED:
case KA_SLOCKED | KA_NOTRECURSED:
case KA_SLOCKED | KA_RECURSED:
slocked = 1;
case KA_LOCKED:
case KA_LOCKED | KA_NOTRECURSED:
case KA_LOCKED | KA_RECURSED:
#ifdef WITNESS
/*
* We cannot trust WITNESS if the lock is held in exclusive
* mode and a call to lockmgr_disown() happened.
* Workaround this skipping the check if the lock is held in
* exclusive mode even for the KA_LOCKED case.
*/
if (slocked || (lk->lk_lock & LK_SHARE)) {
witness_assert(&lk->lock_object, what, file, line);
break;
}
#endif
if (lk->lk_lock == LK_UNLOCKED ||
((lk->lk_lock & LK_SHARE) == 0 && (slocked ||
(!lockmgr_xlocked(lk) && !lockmgr_disowned(lk)))))
panic("Lock %s not %slocked @ %s:%d\n",
lk->lock_object.lo_name, slocked ? "share" : "",
file, line);
if ((lk->lk_lock & LK_SHARE) == 0) {
if (lockmgr_recursed(lk)) {
if (what & KA_NOTRECURSED)
panic("Lock %s recursed @ %s:%d\n",
lk->lock_object.lo_name, file,
line);
} else if (what & KA_RECURSED)
panic("Lock %s not recursed @ %s:%d\n",
lk->lock_object.lo_name, file, line);
}
break;
case KA_XLOCKED:
case KA_XLOCKED | KA_NOTRECURSED:
case KA_XLOCKED | KA_RECURSED:
if (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk))
panic("Lock %s not exclusively locked @ %s:%d\n",
lk->lock_object.lo_name, file, line);
if (lockmgr_recursed(lk)) {
if (what & KA_NOTRECURSED)
panic("Lock %s recursed @ %s:%d\n",
lk->lock_object.lo_name, file, line);
} else if (what & KA_RECURSED)
panic("Lock %s not recursed @ %s:%d\n",
lk->lock_object.lo_name, file, line);
break;
case KA_UNLOCKED:
if (lockmgr_xlocked(lk) || lockmgr_disowned(lk))
panic("Lock %s exclusively locked @ %s:%d\n",
lk->lock_object.lo_name, file, line);
break;
default:
panic("Unknown lockmgr assertion: %d @ %s:%d\n", what, file,
line);
}
}
#endif
#ifdef DDB
int
lockmgr_chain(struct thread *td, struct thread **ownerp)
{
struct lock *lk;
lk = td->td_wchan;
if (LOCK_CLASS(&lk->lock_object) != &lock_class_lockmgr)
return (0);
db_printf("blocked on lockmgr %s", lk->lock_object.lo_name);
if (lk->lk_lock & LK_SHARE)
db_printf("SHARED (count %ju)\n",
(uintmax_t)LK_SHARERS(lk->lk_lock));
else
db_printf("EXCL\n");
*ownerp = lockmgr_xholder(lk);
return (1);
}
static void
db_show_lockmgr(const struct lock_object *lock)
{
struct thread *td;
const struct lock *lk;
lk = (const struct lock *)lock;
db_printf(" state: ");
if (lk->lk_lock == LK_UNLOCKED)
db_printf("UNLOCKED\n");
else if (lk->lk_lock & LK_SHARE)
db_printf("SLOCK: %ju\n", (uintmax_t)LK_SHARERS(lk->lk_lock));
else {
td = lockmgr_xholder(lk);
if (td == (struct thread *)LK_KERNPROC)
db_printf("XLOCK: LK_KERNPROC\n");
else
db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
td->td_tid, td->td_proc->p_pid,
td->td_proc->p_comm);
if (lockmgr_recursed(lk))
db_printf(" recursed: %d\n", lk->lk_recurse);
}
db_printf(" waiters: ");
switch (lk->lk_lock & LK_ALL_WAITERS) {
case LK_SHARED_WAITERS:
db_printf("shared\n");
break;
case LK_EXCLUSIVE_WAITERS:
db_printf("exclusive\n");
break;
case LK_ALL_WAITERS:
db_printf("shared and exclusive\n");
break;
default:
db_printf("none\n");
}
db_printf(" spinners: ");
if (lk->lk_lock & LK_EXCLUSIVE_SPINNERS)
db_printf("exclusive\n");
else
db_printf("none\n");
}
#endif
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