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freebsd-dev/sys/kern/subr_turnstile.c
Bosko Milekic 5746a1d866 - Place back STR string declarations for lock/unlock strings used for KTR_LOCK 
tracing in order to avoid duplication.
- Insert some tracepoints back into the mutex acq/rel code, thus ensuring
  that we can trace all lock acq/rel's again.
- All CURPROC != NULL checks are MPASS()es (under MUTEX_DEBUG) because they
  signify a serious mutex corruption.
- Change up some KASSERT()s to MPASS()es, and vice-versa, depending on the
  type of problem we're debugging (INVARIANTS is used here to check that
  the API is being used properly whereas MUTEX_DEBUG is used to ensure that
  something general isn't happening that will have bad impact on mutex
  locks).

Reminded by: jhb, jake, asmodai
2001-02-11 02:54:16 +00:00

1706 lines
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/*-
* Copyright (c) 1998 Berkeley Software Design, Inc. 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, 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. Berkeley Software Design Inc's name may not be used to endorse or
* promote products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``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 BERKELEY SOFTWARE DESIGN INC 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.
*
* from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
* and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
* $FreeBSD$
*/
/*
* Machine independent bits of mutex implementation and implementation of
* `witness' structure & related debugging routines.
*/
/*
* Main Entry: witness
* Pronunciation: 'wit-n&s
* Function: noun
* Etymology: Middle English witnesse, from Old English witnes knowledge,
* testimony, witness, from 2wit
* Date: before 12th century
* 1 : attestation of a fact or event : TESTIMONY
* 2 : one that gives evidence; specifically : one who testifies in
* a cause or before a judicial tribunal
* 3 : one asked to be present at a transaction so as to be able to
* testify to its having taken place
* 4 : one who has personal knowledge of something
* 5 a : something serving as evidence or proof : SIGN
* b : public affirmation by word or example of usually
* religious faith or conviction <the heroic witness to divine
* life -- Pilot>
* 6 capitalized : a member of the Jehovah's Witnesses
*/
#include "opt_ddb.h"
#include "opt_witness.h"
#include <sys/param.h>
#include <sys/bus.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/vmmeter.h>
#include <sys/ktr.h>
#include <machine/atomic.h>
#include <machine/bus.h>
#include <machine/clock.h>
#include <machine/cpu.h>
#include <ddb/ddb.h>
#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <sys/mutex.h>
/*
* The WITNESS-enabled mutex debug structure.
*/
#ifdef WITNESS
struct mtx_debug {
struct witness *mtxd_witness;
LIST_ENTRY(mtx) mtxd_held;
const char *mtxd_file;
int mtxd_line;
};
#define mtx_held mtx_debug->mtxd_held
#define mtx_file mtx_debug->mtxd_file
#define mtx_line mtx_debug->mtxd_line
#define mtx_witness mtx_debug->mtxd_witness
#endif /* WITNESS */
/*
* Internal utility macros.
*/
#define mtx_unowned(m) ((m)->mtx_lock == MTX_UNOWNED)
#define mtx_owner(m) (mtx_unowned((m)) ? NULL \
: (struct proc *)((m)->mtx_lock & MTX_FLAGMASK))
#define RETIP(x) *(((uintptr_t *)(&x)) - 1)
#define SET_PRIO(p, pri) (p)->p_priority = (pri)
/*
* Early WITNESS-enabled declarations.
*/
#ifdef WITNESS
/*
* Internal WITNESS routines which must be prototyped early.
*
* XXX: When/if witness code is cleaned up, it would be wise to place all
* witness prototyping early in this file.
*/
static void witness_init(struct mtx *, int flag);
static void witness_destroy(struct mtx *);
static void witness_display(void(*)(const char *fmt, ...));
MALLOC_DEFINE(M_WITNESS, "witness", "witness mtx_debug structure");
/* All mutexes in system (used for debug/panic) */
static struct mtx_debug all_mtx_debug = { NULL, {NULL, NULL}, NULL, 0 };
/*
* This global is set to 0 once it becomes safe to use the witness code.
*/
static int witness_cold = 1;
#else /* WITNESS */
/* XXX XXX XXX
* flag++ is sleazoid way of shuting up warning
*/
#define witness_init(m, flag) flag++
#define witness_destroy(m)
#define witness_try_enter(m, t, f, l)
#endif /* WITNESS */
/*
* All mutex locks in system are kept on the all_mtx list.
*/
static struct mtx all_mtx = { MTX_UNOWNED, 0, 0, 0, "All mutexes queue head",
TAILQ_HEAD_INITIALIZER(all_mtx.mtx_blocked),
{ NULL, NULL }, &all_mtx, &all_mtx,
#ifdef WITNESS
&all_mtx_debug
#else
NULL
#endif
};
/*
* Global variables for book keeping.
*/
static int mtx_cur_cnt;
static int mtx_max_cnt;
/*
* Couple of strings for KTR_LOCK tracing in order to avoid duplicates.
*/
char STR_mtx_lock_slp[] = "GOT (sleep) %s [%p] r=%d at %s:%d";
char STR_mtx_unlock_slp[] = "REL (sleep) %s [%p] r=%d at %s:%d";
char STR_mtx_lock_spn[] = "GOT (spin) %s [%p] r=%d at %s:%d";
char STR_mtx_unlock_spn[] = "REL (spin) %s [%p] r=%d at %s:%d";
/*
* Prototypes for non-exported routines.
*
* NOTE: Prototypes for witness routines are placed at the bottom of the file.
*/
static void propagate_priority(struct proc *);
static void
propagate_priority(struct proc *p)
{
int pri = p->p_priority;
struct mtx *m = p->p_blocked;
mtx_assert(&sched_lock, MA_OWNED);
for (;;) {
struct proc *p1;
p = mtx_owner(m);
if (p == NULL) {
/*
* This really isn't quite right. Really
* ought to bump priority of process that
* next acquires the mutex.
*/
MPASS(m->mtx_lock == MTX_CONTESTED);
return;
}
MPASS(p->p_magic == P_MAGIC);
KASSERT(p->p_stat != SSLEEP, ("sleeping process owns a mutex"));
if (p->p_priority <= pri)
return;
/*
* Bump this process' priority.
*/
SET_PRIO(p, pri);
/*
* If lock holder is actually running, just bump priority.
*/
#ifdef SMP
/*
* For SMP, we can check the p_oncpu field to see if we are
* running.
*/
if (p->p_oncpu != 0xff) {
MPASS(p->p_stat == SRUN || p->p_stat == SZOMB);
return;
}
#else
/*
* For UP, we check to see if p is curproc (this shouldn't
* ever happen however as it would mean we are in a deadlock.)
*/
if (p == curproc) {
panic("Deadlock detected");
return;
}
#endif
/*
* If on run queue move to new run queue, and
* quit.
*/
if (p->p_stat == SRUN) {
printf("XXX: moving proc %d(%s) to a new run queue\n",
p->p_pid, p->p_comm);
MPASS(p->p_blocked == NULL);
remrunqueue(p);
setrunqueue(p);
return;
}
/*
* If we aren't blocked on a mutex, we should be.
*/
KASSERT(p->p_stat == SMTX, (
"process %d(%s):%d holds %s but isn't blocked on a mutex\n",
p->p_pid, p->p_comm, p->p_stat,
m->mtx_description));
/*
* Pick up the mutex that p is blocked on.
*/
m = p->p_blocked;
MPASS(m != NULL);
printf("XXX: process %d(%s) is blocked on %s\n", p->p_pid,
p->p_comm, m->mtx_description);
/*
* Check if the proc needs to be moved up on
* the blocked chain
*/
if (p == TAILQ_FIRST(&m->mtx_blocked)) {
printf("XXX: process at head of run queue\n");
continue;
}
p1 = TAILQ_PREV(p, rq, p_procq);
if (p1->p_priority <= pri) {
printf(
"XXX: previous process %d(%s) has higher priority\n",
p->p_pid, p->p_comm);
continue;
}
/*
* Remove proc from blocked chain and determine where
* it should be moved up to. Since we know that p1 has
* a lower priority than p, we know that at least one
* process in the chain has a lower priority and that
* p1 will thus not be NULL after the loop.
*/
TAILQ_REMOVE(&m->mtx_blocked, p, p_procq);
TAILQ_FOREACH(p1, &m->mtx_blocked, p_procq) {
MPASS(p1->p_magic == P_MAGIC);
if (p1->p_priority > pri)
break;
}
MPASS(p1 != NULL);
TAILQ_INSERT_BEFORE(p1, p, p_procq);
CTR4(KTR_LOCK,
"propagate_priority: p %p moved before %p on [%p] %s",
p, p1, m, m->mtx_description);
}
}
/*
* The important part of mtx_trylock{,_flags}()
* Tries to acquire lock `m.' We do NOT handle recursion here; we assume that
* if we're called, it's because we know we don't already own this lock.
*/
int
_mtx_trylock(struct mtx *m, int opts, const char *file, int line)
{
int rval;
MPASS(CURPROC != NULL);
/*
* _mtx_trylock does not accept MTX_NOSWITCH option.
*/
KASSERT((opts & MTX_NOSWITCH) == 0,
("mtx_trylock() called with invalid option flag(s) %d", opts));
rval = _obtain_lock(m, CURTHD);
#ifdef WITNESS
if (rval && m->mtx_witness != NULL) {
/*
* We do not handle recursion in _mtx_trylock; see the
* note at the top of the routine.
*/
KASSERT(!mtx_recursed(m),
("mtx_trylock() called on a recursed mutex"));
witness_try_enter(m, (opts | m->mtx_flags), file, line);
}
#endif /* WITNESS */
if ((opts & MTX_QUIET) == 0)
CTR5(KTR_LOCK, "TRY_ENTER %s [%p] result=%d at %s:%d",
m->mtx_description, m, rval, file, line);
return rval;
}
/*
* _mtx_lock_sleep: the tougher part of acquiring an MTX_DEF lock.
*
* We call this if the lock is either contested (i.e. we need to go to
* sleep waiting for it), or if we need to recurse on it.
*/
void
_mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
{
struct proc *p = CURPROC;
if ((m->mtx_lock & MTX_FLAGMASK) == (uintptr_t)p) {
m->mtx_recurse++;
atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
if ((opts & MTX_QUIET) == 0)
CTR1(KTR_LOCK, "_mtx_lock_sleep: %p recursing", m);
return;
}
if ((opts & MTX_QUIET) == 0)
CTR3(KTR_LOCK, "_mtx_lock_sleep: %p contested (lock=%p) [%p]",
m, (void *)m->mtx_lock, (void *)RETIP(m));
/*
* Save our priority. Even though p_nativepri is protected by
* sched_lock, we don't obtain it here as it can be expensive.
* Since this is the only place p_nativepri is set, and since two
* CPUs will not be executing the same process concurrently, we know
* that no other CPU is going to be messing with this. Also,
* p_nativepri is only read when we are blocked on a mutex, so that
* can't be happening right now either.
*/
p->p_nativepri = p->p_priority;
while (!_obtain_lock(m, p)) {
uintptr_t v;
struct proc *p1;
mtx_lock_spin(&sched_lock);
/*
* Check if the lock has been released while spinning for
* the sched_lock.
*/
if ((v = m->mtx_lock) == MTX_UNOWNED) {
mtx_unlock_spin(&sched_lock);
continue;
}
/*
* The mutex was marked contested on release. This means that
* there are processes blocked on it.
*/
if (v == MTX_CONTESTED) {
p1 = TAILQ_FIRST(&m->mtx_blocked);
MPASS(p1 != NULL);
m->mtx_lock = (uintptr_t)p | MTX_CONTESTED;
if (p1->p_priority < p->p_priority)
SET_PRIO(p, p1->p_priority);
mtx_unlock_spin(&sched_lock);
return;
}
/*
* If the mutex isn't already contested and a failure occurs
* setting the contested bit, the mutex was either released
* or the state of the MTX_RECURSED bit changed.
*/
if ((v & MTX_CONTESTED) == 0 &&
!atomic_cmpset_ptr(&m->mtx_lock, (void *)v,
(void *)(v | MTX_CONTESTED))) {
mtx_unlock_spin(&sched_lock);
continue;
}
/*
* We deffinately must sleep for this lock.
*/
mtx_assert(m, MA_NOTOWNED);
#ifdef notyet
/*
* If we're borrowing an interrupted thread's VM context, we
* must clean up before going to sleep.
*/
if (p->p_flag & (P_ITHD | P_SITHD)) {
ithd_t *it = (ithd_t *)p;
if (it->it_interrupted) {
if ((opts & MTX_QUIET) == 0)
CTR2(KTR_LOCK,
"_mtx_lock_sleep: 0x%x interrupted 0x%x",
it, it->it_interrupted);
intr_thd_fixup(it);
}
}
#endif
/*
* Put us on the list of threads blocked on this mutex.
*/
if (TAILQ_EMPTY(&m->mtx_blocked)) {
p1 = (struct proc *)(m->mtx_lock & MTX_FLAGMASK);
LIST_INSERT_HEAD(&p1->p_contested, m, mtx_contested);
TAILQ_INSERT_TAIL(&m->mtx_blocked, p, p_procq);
} else {
TAILQ_FOREACH(p1, &m->mtx_blocked, p_procq)
if (p1->p_priority > p->p_priority)
break;
if (p1)
TAILQ_INSERT_BEFORE(p1, p, p_procq);
else
TAILQ_INSERT_TAIL(&m->mtx_blocked, p, p_procq);
}
/*
* Save who we're blocked on.
*/
p->p_blocked = m;
p->p_mtxname = m->mtx_description;
p->p_stat = SMTX;
#if 0
propagate_priority(p);
#endif
if ((opts & MTX_QUIET) == 0)
CTR3(KTR_LOCK,
"_mtx_lock_sleep: p %p blocked on [%p] %s", p, m,
m->mtx_description);
mi_switch();
if ((opts & MTX_QUIET) == 0)
CTR3(KTR_LOCK,
"_mtx_lock_sleep: p %p free from blocked on [%p] %s",
p, m, m->mtx_description);
mtx_unlock_spin(&sched_lock);
}
return;
}
/*
* _mtx_lock_spin: the tougher part of acquiring an MTX_SPIN lock.
*
* This is only called if we need to actually spin for the lock. Recursion
* is handled inline.
*/
void
_mtx_lock_spin(struct mtx *m, int opts, u_int mtx_intr, const char *file,
int line)
{
int i = 0;
if ((opts & MTX_QUIET) == 0)
CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
for (;;) {
if (_obtain_lock(m, CURPROC))
break;
while (m->mtx_lock != MTX_UNOWNED) {
if (i++ < 1000000)
continue;
if (i++ < 6000000)
DELAY(1);
#ifdef DDB
else if (!db_active)
#else
else
#endif
panic("spin lock %s held by %p for > 5 seconds",
m->mtx_description, (void *)m->mtx_lock);
}
}
m->mtx_saveintr = mtx_intr;
if ((opts & MTX_QUIET) == 0)
CTR1(KTR_LOCK, "_mtx_lock_spin: %p spin done", m);
return;
}
/*
* _mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock.
*
* We are only called here if the lock is recursed or contested (i.e. we
* need to wake up a blocked thread).
*/
void
_mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
{
struct proc *p, *p1;
struct mtx *m1;
int pri;
p = CURPROC;
MPASS4(mtx_owned(m), "mtx_owned(mpp)", file, line);
if (mtx_recursed(m)) {
if (--(m->mtx_recurse) == 0)
atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED);
if ((opts & MTX_QUIET) == 0)
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p unrecurse", m);
return;
}
mtx_lock_spin(&sched_lock);
if ((opts & MTX_QUIET) == 0)
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
p1 = TAILQ_FIRST(&m->mtx_blocked);
MPASS(p->p_magic == P_MAGIC);
MPASS(p1->p_magic == P_MAGIC);
TAILQ_REMOVE(&m->mtx_blocked, p1, p_procq);
if (TAILQ_EMPTY(&m->mtx_blocked)) {
LIST_REMOVE(m, mtx_contested);
_release_lock_quick(m);
if ((opts & MTX_QUIET) == 0)
CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p not held", m);
} else
atomic_store_rel_ptr(&m->mtx_lock, (void *)MTX_CONTESTED);
pri = MAXPRI;
LIST_FOREACH(m1, &p->p_contested, mtx_contested) {
int cp = TAILQ_FIRST(&m1->mtx_blocked)->p_priority;
if (cp < pri)
pri = cp;
}
if (pri > p->p_nativepri)
pri = p->p_nativepri;
SET_PRIO(p, pri);
if ((opts & MTX_QUIET) == 0)
CTR2(KTR_LOCK, "_mtx_unlock_sleep: %p contested setrunqueue %p",
m, p1);
p1->p_blocked = NULL;
p1->p_mtxname = NULL;
p1->p_stat = SRUN;
setrunqueue(p1);
if ((opts & MTX_NOSWITCH) == 0 && p1->p_priority < pri) {
#ifdef notyet
if (p->p_flag & (P_ITHD | P_SITHD)) {
ithd_t *it = (ithd_t *)p;
if (it->it_interrupted) {
if ((opts & MTX_QUIET) == 0)
CTR2(KTR_LOCK,
"_mtx_unlock_sleep: 0x%x interrupted 0x%x",
it, it->it_interrupted);
intr_thd_fixup(it);
}
}
#endif
setrunqueue(p);
if ((opts & MTX_QUIET) == 0)
CTR2(KTR_LOCK,
"_mtx_unlock_sleep: %p switching out lock=%p", m,
(void *)m->mtx_lock);
mi_switch();
if ((opts & MTX_QUIET) == 0)
CTR2(KTR_LOCK, "_mtx_unlock_sleep: %p resuming lock=%p",
m, (void *)m->mtx_lock);
}
mtx_unlock_spin(&sched_lock);
return;
}
/*
* All the unlocking of MTX_SPIN locks is done inline.
* See the _rel_spin_lock() macro for the details.
*/
/*
* The INVARIANTS-enabled mtx_assert()
*/
#ifdef INVARIANTS
void
_mtx_assert(struct mtx *m, int what, const char *file, int line)
{
switch ((what)) {
case MA_OWNED:
case MA_OWNED | MA_RECURSED:
case MA_OWNED | MA_NOTRECURSED:
if (!mtx_owned((m)))
panic("mutex %s not owned at %s:%d",
(m)->mtx_description, file, line);
if (mtx_recursed((m))) {
if (((what) & MA_NOTRECURSED) != 0)
panic("mutex %s recursed at %s:%d",
(m)->mtx_description, file, line);
} else if (((what) & MA_RECURSED) != 0) {
panic("mutex %s unrecursed at %s:%d",
(m)->mtx_description, file, line);
}
break;
case MA_NOTOWNED:
if (mtx_owned((m)))
panic("mutex %s owned at %s:%d",
(m)->mtx_description, file, line);
break;
default:
panic("unknown mtx_assert at %s:%d", file, line);
}
}
#endif
/*
* The MUTEX_DEBUG-enabled mtx_validate()
*/
#define MV_DESTROY 0 /* validate before destory */
#define MV_INIT 1 /* validate before init */
#ifdef MUTEX_DEBUG
int mtx_validate __P((struct mtx *, int));
int
mtx_validate(struct mtx *m, int when)
{
struct mtx *mp;
int i;
int retval = 0;
#ifdef WITNESS
if (witness_cold)
return 0;
#endif
if (m == &all_mtx || cold)
return 0;
mtx_lock(&all_mtx);
/*
* XXX - When kernacc() is fixed on the alpha to handle K0_SEG memory properly
* we can re-enable the kernacc() checks.
*/
#ifndef __alpha__
MPASS(kernacc((caddr_t)all_mtx.mtx_next, sizeof(uintptr_t),
VM_PROT_READ) == 1);
#endif
MPASS(all_mtx.mtx_next->mtx_prev == &all_mtx);
for (i = 0, mp = all_mtx.mtx_next; mp != &all_mtx; mp = mp->mtx_next) {
#ifndef __alpha__
if (kernacc((caddr_t)mp->mtx_next, sizeof(uintptr_t),
VM_PROT_READ) != 1) {
panic("mtx_validate: mp=%p mp->mtx_next=%p",
mp, mp->mtx_next);
}
#endif
i++;
if (i > mtx_cur_cnt) {
panic("mtx_validate: too many in chain, known=%d\n",
mtx_cur_cnt);
}
}
MPASS(i == mtx_cur_cnt);
switch (when) {
case MV_DESTROY:
for (mp = all_mtx.mtx_next; mp != &all_mtx; mp = mp->mtx_next)
if (mp == m)
break;
MPASS(mp == m);
break;
case MV_INIT:
for (mp = all_mtx.mtx_next; mp != &all_mtx; mp = mp->mtx_next)
if (mp == m) {
/*
* Not good. This mutex already exists.
*/
printf("re-initing existing mutex %s\n",
m->mtx_description);
MPASS(m->mtx_lock == MTX_UNOWNED);
retval = 1;
}
}
mtx_unlock(&all_mtx);
return (retval);
}
#endif
/*
* Mutex initialization routine; initialize lock `m' of type contained in
* `opts' with options contained in `opts' and description `description.'
* Place on "all_mtx" queue.
*/
void
mtx_init(struct mtx *m, const char *description, int opts)
{
if ((opts & MTX_QUIET) == 0)
CTR2(KTR_LOCK, "mtx_init %p (%s)", m, description);
#ifdef MUTEX_DEBUG
/* Diagnostic and error correction */
if (mtx_validate(m, MV_INIT))
return;
#endif
bzero((void *)m, sizeof *m);
TAILQ_INIT(&m->mtx_blocked);
#ifdef WITNESS
if (!witness_cold) {
m->mtx_debug = malloc(sizeof(struct mtx_debug),
M_WITNESS, M_NOWAIT | M_ZERO);
MPASS(m->mtx_debug != NULL);
}
#endif
m->mtx_description = description;
m->mtx_flags = opts;
m->mtx_lock = MTX_UNOWNED;
/* Put on all mutex queue */
mtx_lock(&all_mtx);
m->mtx_next = &all_mtx;
m->mtx_prev = all_mtx.mtx_prev;
m->mtx_prev->mtx_next = m;
all_mtx.mtx_prev = m;
if (++mtx_cur_cnt > mtx_max_cnt)
mtx_max_cnt = mtx_cur_cnt;
mtx_unlock(&all_mtx);
#ifdef WITNESS
if (!witness_cold)
witness_init(m, opts);
#endif
}
/*
* Remove lock `m' from all_mtx queue.
*/
void
mtx_destroy(struct mtx *m)
{
#ifdef WITNESS
KASSERT(!witness_cold, ("%s: Cannot destroy while still cold\n",
__FUNCTION__));
#endif
CTR2(KTR_LOCK, "mtx_destroy %p (%s)", m, m->mtx_description);
#ifdef MUTEX_DEBUG
if (m->mtx_next == NULL)
panic("mtx_destroy: %p (%s) already destroyed",
m, m->mtx_description);
if (!mtx_owned(m)) {
MPASS(m->mtx_lock == MTX_UNOWNED);
} else {
MPASS((m->mtx_lock & (MTX_RECURSED|MTX_CONTESTED)) == 0);
}
/* diagnostic */
mtx_validate(m, MV_DESTROY);
#endif
#ifdef WITNESS
if (m->mtx_witness)
witness_destroy(m);
#endif /* WITNESS */
/* Remove from the all mutex queue */
mtx_lock(&all_mtx);
m->mtx_next->mtx_prev = m->mtx_prev;
m->mtx_prev->mtx_next = m->mtx_next;
#ifdef MUTEX_DEBUG
m->mtx_next = m->mtx_prev = NULL;
#endif
#ifdef WITNESS
free(m->mtx_debug, M_WITNESS);
m->mtx_debug = NULL;
#endif
mtx_cur_cnt--;
mtx_unlock(&all_mtx);
}
/*
* The WITNESS-enabled diagnostic code.
*/
#ifdef WITNESS
static void
witness_fixup(void *dummy __unused)
{
struct mtx *mp;
/*
* We have to release Giant before initializing its witness
* structure so that WITNESS doesn't get confused.
*/
mtx_unlock(&Giant);
mtx_assert(&Giant, MA_NOTOWNED);
mtx_lock(&all_mtx);
/* Iterate through all mutexes and finish up mutex initialization. */
for (mp = all_mtx.mtx_next; mp != &all_mtx; mp = mp->mtx_next) {
mp->mtx_debug = malloc(sizeof(struct mtx_debug),
M_WITNESS, M_NOWAIT | M_ZERO);
MPASS(mp->mtx_debug != NULL);
witness_init(mp, mp->mtx_flags);
}
mtx_unlock(&all_mtx);
/* Mark the witness code as being ready for use. */
atomic_store_rel_int(&witness_cold, 0);
mtx_lock(&Giant);
}
SYSINIT(wtnsfxup, SI_SUB_MUTEX, SI_ORDER_FIRST, witness_fixup, NULL)
#define WITNESS_COUNT 200
#define WITNESS_NCHILDREN 2
int witness_watch = 1;
struct witness {
struct witness *w_next;
const char *w_description;
const char *w_file;
int w_line;
struct witness *w_morechildren;
u_char w_childcnt;
u_char w_Giant_squawked:1;
u_char w_other_squawked:1;
u_char w_same_squawked:1;
u_char w_spin:1; /* MTX_SPIN type mutex. */
u_int w_level;
struct witness *w_children[WITNESS_NCHILDREN];
};
struct witness_blessed {
char *b_lock1;
char *b_lock2;
};
#ifdef DDB
/*
* When DDB is enabled and witness_ddb is set to 1, it will cause the system to
* drop into kdebug() when:
* - a lock heirarchy violation occurs
* - locks are held when going to sleep.
*/
int witness_ddb;
#ifdef WITNESS_DDB
TUNABLE_INT_DECL("debug.witness_ddb", 1, witness_ddb);
#else
TUNABLE_INT_DECL("debug.witness_ddb", 0, witness_ddb);
#endif
SYSCTL_INT(_debug, OID_AUTO, witness_ddb, CTLFLAG_RW, &witness_ddb, 0, "");
#endif /* DDB */
int witness_skipspin;
#ifdef WITNESS_SKIPSPIN
TUNABLE_INT_DECL("debug.witness_skipspin", 1, witness_skipspin);
#else
TUNABLE_INT_DECL("debug.witness_skipspin", 0, witness_skipspin);
#endif
SYSCTL_INT(_debug, OID_AUTO, witness_skipspin, CTLFLAG_RD, &witness_skipspin, 0,
"");
/*
* Witness-enabled globals
*/
static struct mtx w_mtx;
static struct witness *w_free;
static struct witness *w_all;
static int w_inited;
static int witness_dead; /* fatal error, probably no memory */
static struct witness w_data[WITNESS_COUNT];
/*
* Internal witness routine prototypes
*/
static struct witness *enroll(const char *description, int flag);
static int itismychild(struct witness *parent, struct witness *child);
static void removechild(struct witness *parent, struct witness *child);
static int isitmychild(struct witness *parent, struct witness *child);
static int isitmydescendant(struct witness *parent, struct witness *child);
static int dup_ok(struct witness *);
static int blessed(struct witness *, struct witness *);
static void
witness_displaydescendants(void(*)(const char *fmt, ...), struct witness *);
static void witness_leveldescendents(struct witness *parent, int level);
static void witness_levelall(void);
static struct witness * witness_get(void);
static void witness_free(struct witness *m);
static char *ignore_list[] = {
"witness lock",
NULL
};
static char *spin_order_list[] = {
#if defined(__i386__) && defined (SMP)
"com",
#endif
"sio",
#ifdef __i386__
"cy",
#endif
"sched lock",
#ifdef __i386__
"clk",
#endif
"callout",
/*
* leaf locks
*/
"ithread table lock",
"ithread list lock",
#ifdef SMP
#ifdef __i386__
"ap boot",
"imen",
#endif
"smp rendezvous",
#endif
NULL
};
static char *order_list[] = {
"Giant", "proctree", "allproc", "process lock", "uidinfo hash",
"uidinfo struct", NULL,
NULL
};
static char *dup_list[] = {
NULL
};
static char *sleep_list[] = {
"Giant",
NULL
};
/*
* Pairs of locks which have been blessed
* Don't complain about order problems with blessed locks
*/
static struct witness_blessed blessed_list[] = {
};
static int blessed_count =
sizeof(blessed_list) / sizeof(struct witness_blessed);
static void
witness_init(struct mtx *m, int flag)
{
m->mtx_witness = enroll(m->mtx_description, flag);
}
static void
witness_destroy(struct mtx *m)
{
struct mtx *m1;
struct proc *p;
p = CURPROC;
LIST_FOREACH(m1, &p->p_heldmtx, mtx_held) {
if (m1 == m) {
LIST_REMOVE(m, mtx_held);
break;
}
}
return;
}
static void
witness_display(void(*prnt)(const char *fmt, ...))
{
struct witness *w, *w1;
int level, found;
KASSERT(!witness_cold, ("%s: witness_cold\n", __FUNCTION__));
witness_levelall();
/*
* First, handle sleep mutexes which have been acquired at least
* once.
*/
prnt("Sleep mutexes:\n");
for (w = w_all; w; w = w->w_next) {
if (w->w_file == NULL || w->w_spin)
continue;
for (w1 = w_all; w1; w1 = w1->w_next) {
if (isitmychild(w1, w))
break;
}
if (w1 != NULL)
continue;
/*
* This lock has no anscestors, display its descendants.
*/
witness_displaydescendants(prnt, w);
}
/*
* Now do spin mutexes which have been acquired at least once.
*/
prnt("\nSpin mutexes:\n");
level = 0;
while (level < sizeof(spin_order_list) / sizeof(char *)) {
found = 0;
for (w = w_all; w; w = w->w_next) {
if (w->w_file == NULL || !w->w_spin)
continue;
if (w->w_level == 1 << level) {
witness_displaydescendants(prnt, w);
level++;
found = 1;
}
}
if (found == 0)
level++;
}
/*
* Finally, any mutexes which have not been acquired yet.
*/
prnt("\nMutexes which were never acquired:\n");
for (w = w_all; w; w = w->w_next) {
if (w->w_file != NULL)
continue;
prnt("%s\n", w->w_description);
}
}
void
witness_enter(struct mtx *m, int flags, const char *file, int line)
{
struct witness *w, *w1;
struct mtx *m1;
struct proc *p;
int i;
#ifdef DDB
int go_into_ddb = 0;
#endif /* DDB */
if (witness_cold || m->mtx_witness == NULL || panicstr)
return;
w = m->mtx_witness;
p = CURPROC;
if (flags & MTX_SPIN) {
if ((m->mtx_flags & MTX_SPIN) == 0)
panic("mutex_enter: MTX_SPIN on MTX_DEF mutex %s @"
" %s:%d", m->mtx_description, file, line);
if (mtx_recursed(m)) {
if ((m->mtx_flags & MTX_RECURSE) == 0)
panic("mutex_enter: recursion on non-recursive"
" mutex %s @ %s:%d", m->mtx_description,
file, line);
return;
}
mtx_lock_spin_flags(&w_mtx, MTX_QUIET);
i = PCPU_GET(witness_spin_check);
if (i != 0 && w->w_level < i) {
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
panic("mutex_enter(%s:%x, MTX_SPIN) out of order @"
" %s:%d already holding %s:%x",
m->mtx_description, w->w_level, file, line,
spin_order_list[ffs(i)-1], i);
}
PCPU_SET(witness_spin_check, i | w->w_level);
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
w->w_file = file;
w->w_line = line;
m->mtx_line = line;
m->mtx_file = file;
return;
}
if ((m->mtx_flags & MTX_SPIN) != 0)
panic("mutex_enter: MTX_DEF on MTX_SPIN mutex %s @ %s:%d",
m->mtx_description, file, line);
if (mtx_recursed(m)) {
if ((m->mtx_flags & MTX_RECURSE) == 0)
panic("mutex_enter: recursion on non-recursive"
" mutex %s @ %s:%d", m->mtx_description,
file, line);
return;
}
if (witness_dead)
goto out;
if (cold)
goto out;
if (!mtx_legal2block())
panic("blockable mtx_lock() of %s when not legal @ %s:%d",
m->mtx_description, file, line);
/*
* Is this the first mutex acquired
*/
if ((m1 = LIST_FIRST(&p->p_heldmtx)) == NULL)
goto out;
if ((w1 = m1->mtx_witness) == w) {
if (w->w_same_squawked || dup_ok(w))
goto out;
w->w_same_squawked = 1;
printf("acquring duplicate lock of same type: \"%s\"\n",
m->mtx_description);
printf(" 1st @ %s:%d\n", w->w_file, w->w_line);
printf(" 2nd @ %s:%d\n", file, line);
#ifdef DDB
go_into_ddb = 1;
#endif /* DDB */
goto out;
}
MPASS(!mtx_owned(&w_mtx));
mtx_lock_spin_flags(&w_mtx, MTX_QUIET);
/*
* If we have a known higher number just say ok
*/
if (witness_watch > 1 && w->w_level > w1->w_level) {
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
goto out;
}
if (isitmydescendant(m1->mtx_witness, w)) {
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
goto out;
}
for (i = 0; m1 != NULL; m1 = LIST_NEXT(m1, mtx_held), i++) {
MPASS(i < 200);
w1 = m1->mtx_witness;
if (isitmydescendant(w, w1)) {
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
if (blessed(w, w1))
goto out;
if (m1 == &Giant) {
if (w1->w_Giant_squawked)
goto out;
else
w1->w_Giant_squawked = 1;
} else {
if (w1->w_other_squawked)
goto out;
else
w1->w_other_squawked = 1;
}
printf("lock order reversal\n");
printf(" 1st %s last acquired @ %s:%d\n",
w->w_description, w->w_file, w->w_line);
printf(" 2nd %p %s @ %s:%d\n",
m1, w1->w_description, w1->w_file, w1->w_line);
printf(" 3rd %p %s @ %s:%d\n",
m, w->w_description, file, line);
#ifdef DDB
go_into_ddb = 1;
#endif /* DDB */
goto out;
}
}
m1 = LIST_FIRST(&p->p_heldmtx);
if (!itismychild(m1->mtx_witness, w))
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
out:
#ifdef DDB
if (witness_ddb && go_into_ddb)
Debugger("witness_enter");
#endif /* DDB */
w->w_file = file;
w->w_line = line;
m->mtx_line = line;
m->mtx_file = file;
/*
* If this pays off it likely means that a mutex being witnessed
* is acquired in hardclock. Put it in the ignore list. It is
* likely not the mutex this assert fails on.
*/
MPASS(m->mtx_held.le_prev == NULL);
LIST_INSERT_HEAD(&p->p_heldmtx, (struct mtx*)m, mtx_held);
}
void
witness_try_enter(struct mtx *m, int flags, const char *file, int line)
{
struct proc *p;
struct witness *w = m->mtx_witness;
if (witness_cold)
return;
if (panicstr)
return;
if (flags & MTX_SPIN) {
if ((m->mtx_flags & MTX_SPIN) == 0)
panic("mutex_try_enter: "
"MTX_SPIN on MTX_DEF mutex %s @ %s:%d",
m->mtx_description, file, line);
if (mtx_recursed(m)) {
if ((m->mtx_flags & MTX_RECURSE) == 0)
panic("mutex_try_enter: recursion on"
" non-recursive mutex %s @ %s:%d",
m->mtx_description, file, line);
return;
}
mtx_lock_spin_flags(&w_mtx, MTX_QUIET);
PCPU_SET(witness_spin_check,
PCPU_GET(witness_spin_check) | w->w_level);
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
w->w_file = file;
w->w_line = line;
m->mtx_line = line;
m->mtx_file = file;
return;
}
if ((m->mtx_flags & MTX_SPIN) != 0)
panic("mutex_try_enter: MTX_DEF on MTX_SPIN mutex %s @ %s:%d",
m->mtx_description, file, line);
if (mtx_recursed(m)) {
if ((m->mtx_flags & MTX_RECURSE) == 0)
panic("mutex_try_enter: recursion on non-recursive"
" mutex %s @ %s:%d", m->mtx_description, file,
line);
return;
}
w->w_file = file;
w->w_line = line;
m->mtx_line = line;
m->mtx_file = file;
p = CURPROC;
MPASS(m->mtx_held.le_prev == NULL);
LIST_INSERT_HEAD(&p->p_heldmtx, (struct mtx*)m, mtx_held);
}
void
witness_exit(struct mtx *m, int flags, const char *file, int line)
{
struct witness *w;
if (witness_cold || m->mtx_witness == NULL || panicstr)
return;
w = m->mtx_witness;
if (flags & MTX_SPIN) {
if ((m->mtx_flags & MTX_SPIN) == 0)
panic("mutex_exit: MTX_SPIN on MTX_DEF mutex %s @"
" %s:%d", m->mtx_description, file, line);
if (mtx_recursed(m)) {
if ((m->mtx_flags & MTX_RECURSE) == 0)
panic("mutex_exit: recursion on non-recursive"
" mutex %s @ %s:%d", m->mtx_description,
file, line);
return;
}
mtx_lock_spin_flags(&w_mtx, MTX_QUIET);
PCPU_SET(witness_spin_check,
PCPU_GET(witness_spin_check) & ~w->w_level);
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
return;
}
if ((m->mtx_flags & MTX_SPIN) != 0)
panic("mutex_exit: MTX_DEF on MTX_SPIN mutex %s @ %s:%d",
m->mtx_description, file, line);
if (mtx_recursed(m)) {
if ((m->mtx_flags & MTX_RECURSE) == 0)
panic("mutex_exit: recursion on non-recursive"
" mutex %s @ %s:%d", m->mtx_description,
file, line);
return;
}
if ((flags & MTX_NOSWITCH) == 0 && !mtx_legal2block() && !cold)
panic("switchable mtx_unlock() of %s when not legal @ %s:%d",
m->mtx_description, file, line);
LIST_REMOVE(m, mtx_held);
m->mtx_held.le_prev = NULL;
}
int
witness_sleep(int check_only, struct mtx *mtx, const char *file, int line)
{
struct mtx *m;
struct proc *p;
char **sleep;
int n = 0;
KASSERT(!witness_cold, ("%s: witness_cold\n", __FUNCTION__));
p = CURPROC;
LIST_FOREACH(m, &p->p_heldmtx, mtx_held) {
if (m == mtx)
continue;
for (sleep = sleep_list; *sleep!= NULL; sleep++)
if (strcmp(m->mtx_description, *sleep) == 0)
goto next;
if (n == 0)
printf("Whee!\n");
printf("%s:%d: %s with \"%s\" locked from %s:%d\n",
file, line, check_only ? "could sleep" : "sleeping",
m->mtx_description,
m->mtx_witness->w_file, m->mtx_witness->w_line);
n++;
next:
}
#ifdef DDB
if (witness_ddb && n)
Debugger("witness_sleep");
#endif /* DDB */
return (n);
}
static struct witness *
enroll(const char *description, int flag)
{
int i;
struct witness *w, *w1;
char **ignore;
char **order;
if (!witness_watch)
return (NULL);
for (ignore = ignore_list; *ignore != NULL; ignore++)
if (strcmp(description, *ignore) == 0)
return (NULL);
if (w_inited == 0) {
mtx_init(&w_mtx, "witness lock", MTX_SPIN);
for (i = 0; i < WITNESS_COUNT; i++) {
w = &w_data[i];
witness_free(w);
}
w_inited = 1;
for (order = order_list; *order != NULL; order++) {
w = enroll(*order, MTX_DEF);
w->w_file = "order list";
for (order++; *order != NULL; order++) {
w1 = enroll(*order, MTX_DEF);
w1->w_file = "order list";
itismychild(w, w1);
w = w1;
}
}
}
if ((flag & MTX_SPIN) && witness_skipspin)
return (NULL);
mtx_lock_spin_flags(&w_mtx, MTX_QUIET);
for (w = w_all; w; w = w->w_next) {
if (strcmp(description, w->w_description) == 0) {
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
return (w);
}
}
if ((w = witness_get()) == NULL)
return (NULL);
w->w_next = w_all;
w_all = w;
w->w_description = description;
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
if (flag & MTX_SPIN) {
w->w_spin = 1;
i = 1;
for (order = spin_order_list; *order != NULL; order++) {
if (strcmp(description, *order) == 0)
break;
i <<= 1;
}
if (*order == NULL)
panic("spin lock %s not in order list", description);
w->w_level = i;
}
return (w);
}
static int
itismychild(struct witness *parent, struct witness *child)
{
static int recursed;
/*
* Insert "child" after "parent"
*/
while (parent->w_morechildren)
parent = parent->w_morechildren;
if (parent->w_childcnt == WITNESS_NCHILDREN) {
if ((parent->w_morechildren = witness_get()) == NULL)
return (1);
parent = parent->w_morechildren;
}
MPASS(child != NULL);
parent->w_children[parent->w_childcnt++] = child;
/*
* now prune whole tree
*/
if (recursed)
return (0);
recursed = 1;
for (child = w_all; child != NULL; child = child->w_next) {
for (parent = w_all; parent != NULL;
parent = parent->w_next) {
if (!isitmychild(parent, child))
continue;
removechild(parent, child);
if (isitmydescendant(parent, child))
continue;
itismychild(parent, child);
}
}
recursed = 0;
witness_levelall();
return (0);
}
static void
removechild(struct witness *parent, struct witness *child)
{
struct witness *w, *w1;
int i;
for (w = parent; w != NULL; w = w->w_morechildren)
for (i = 0; i < w->w_childcnt; i++)
if (w->w_children[i] == child)
goto found;
return;
found:
for (w1 = w; w1->w_morechildren != NULL; w1 = w1->w_morechildren)
continue;
w->w_children[i] = w1->w_children[--w1->w_childcnt];
MPASS(w->w_children[i] != NULL);
if (w1->w_childcnt != 0)
return;
if (w1 == parent)
return;
for (w = parent; w->w_morechildren != w1; w = w->w_morechildren)
continue;
w->w_morechildren = 0;
witness_free(w1);
}
static int
isitmychild(struct witness *parent, struct witness *child)
{
struct witness *w;
int i;
for (w = parent; w != NULL; w = w->w_morechildren) {
for (i = 0; i < w->w_childcnt; i++) {
if (w->w_children[i] == child)
return (1);
}
}
return (0);
}
static int
isitmydescendant(struct witness *parent, struct witness *child)
{
struct witness *w;
int i;
int j;
for (j = 0, w = parent; w != NULL; w = w->w_morechildren, j++) {
MPASS(j < 1000);
for (i = 0; i < w->w_childcnt; i++) {
if (w->w_children[i] == child)
return (1);
}
for (i = 0; i < w->w_childcnt; i++) {
if (isitmydescendant(w->w_children[i], child))
return (1);
}
}
return (0);
}
void
witness_levelall (void)
{
struct witness *w, *w1;
for (w = w_all; w; w = w->w_next)
if (!(w->w_spin))
w->w_level = 0;
for (w = w_all; w; w = w->w_next) {
if (w->w_spin)
continue;
for (w1 = w_all; w1; w1 = w1->w_next) {
if (isitmychild(w1, w))
break;
}
if (w1 != NULL)
continue;
witness_leveldescendents(w, 0);
}
}
static void
witness_leveldescendents(struct witness *parent, int level)
{
int i;
struct witness *w;
if (parent->w_level < level)
parent->w_level = level;
level++;
for (w = parent; w != NULL; w = w->w_morechildren)
for (i = 0; i < w->w_childcnt; i++)
witness_leveldescendents(w->w_children[i], level);
}
static void
witness_displaydescendants(void(*prnt)(const char *fmt, ...),
struct witness *parent)
{
struct witness *w;
int i;
int level;
level = parent->w_spin ? ffs(parent->w_level) : parent->w_level;
prnt("%d", level);
if (level < 10)
prnt(" ");
for (i = 0; i < level; i++)
prnt(" ");
prnt("%s", parent->w_description);
if (parent->w_file != NULL)
prnt(" -- last acquired @ %s:%d\n", parent->w_file,
parent->w_line);
for (w = parent; w != NULL; w = w->w_morechildren)
for (i = 0; i < w->w_childcnt; i++)
witness_displaydescendants(prnt, w->w_children[i]);
}
static int
dup_ok(struct witness *w)
{
char **dup;
for (dup = dup_list; *dup!= NULL; dup++)
if (strcmp(w->w_description, *dup) == 0)
return (1);
return (0);
}
static int
blessed(struct witness *w1, struct witness *w2)
{
int i;
struct witness_blessed *b;
for (i = 0; i < blessed_count; i++) {
b = &blessed_list[i];
if (strcmp(w1->w_description, b->b_lock1) == 0) {
if (strcmp(w2->w_description, b->b_lock2) == 0)
return (1);
continue;
}
if (strcmp(w1->w_description, b->b_lock2) == 0)
if (strcmp(w2->w_description, b->b_lock1) == 0)
return (1);
}
return (0);
}
static struct witness *
witness_get()
{
struct witness *w;
if ((w = w_free) == NULL) {
witness_dead = 1;
mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
printf("witness exhausted\n");
return (NULL);
}
w_free = w->w_next;
bzero(w, sizeof(*w));
return (w);
}
static void
witness_free(struct witness *w)
{
w->w_next = w_free;
w_free = w;
}
int
witness_list(struct proc *p)
{
struct mtx *m;
int nheld;
KASSERT(!witness_cold, ("%s: witness_cold\n", __FUNCTION__));
nheld = 0;
LIST_FOREACH(m, &p->p_heldmtx, mtx_held) {
printf("\t\"%s\" (%p) locked at %s:%d\n",
m->mtx_description, m,
m->mtx_witness->w_file, m->mtx_witness->w_line);
nheld++;
}
return (nheld);
}
#ifdef DDB
DB_SHOW_COMMAND(mutexes, db_witness_list)
{
witness_list(CURPROC);
}
DB_SHOW_COMMAND(witness, db_witness_display)
{
witness_display(db_printf);
}
#endif
void
witness_save(struct mtx *m, const char **filep, int *linep)
{
KASSERT(!witness_cold, ("%s: witness_cold\n", __FUNCTION__));
if (m->mtx_witness == NULL)
return;
*filep = m->mtx_witness->w_file;
*linep = m->mtx_witness->w_line;
}
void
witness_restore(struct mtx *m, const char *file, int line)
{
KASSERT(!witness_cold, ("%s: witness_cold\n", __FUNCTION__));
if (m->mtx_witness == NULL)
return;
m->mtx_witness->w_file = file;
m->mtx_witness->w_line = line;
}
#endif /* WITNESS */
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