/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org>
*
* 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 AUTHOR 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 AUTHOR 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.
*/
/*
* Machine independent bits of reader/writer lock implementation.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_ddb.h"
#include "opt_hwpmc_hooks.h"
#include "opt_no_adaptive_rwlocks.h"
#include <sys/param.h>
#include <sys/kdb.h>
#include <sys/ktr.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/rwlock.h>
#include <sys/sched.h>
#include <sys/smp.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/turnstile.h>
#include <machine/cpu.h>
#if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS)
#define ADAPTIVE_RWLOCKS
#endif
#ifdef HWPMC_HOOKS
#include <sys/pmckern.h>
PMC_SOFT_DECLARE( , , lock, failed);
#endif
/*
* Return the rwlock address when the lock cookie address is provided.
* This functionality assumes that struct rwlock* have a member named rw_lock.
*/
#define rwlock2rw(c) (__containerof(c, struct rwlock, rw_lock))
#ifdef DDB
#include <ddb/ddb.h>
static void db_show_rwlock(const struct lock_object *lock);
#endif
static void assert_rw(const struct lock_object *lock, int what);
static void lock_rw(struct lock_object *lock, uintptr_t how);
#ifdef KDTRACE_HOOKS
static int owner_rw(const struct lock_object *lock, struct thread **owner);
#endif
static uintptr_t unlock_rw(struct lock_object *lock);
struct lock_class lock_class_rw = {
.lc_name = "rw",
.lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE,
.lc_assert = assert_rw,
#ifdef DDB
.lc_ddb_show = db_show_rwlock,
#endif
.lc_lock = lock_rw,
.lc_unlock = unlock_rw,
#ifdef KDTRACE_HOOKS
.lc_owner = owner_rw,
#endif
};
#ifdef ADAPTIVE_RWLOCKS
#ifdef RWLOCK_CUSTOM_BACKOFF
static u_short __read_frequently rowner_retries;
static u_short __read_frequently rowner_loops;
static SYSCTL_NODE(_debug, OID_AUTO, rwlock,
CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
"rwlock debugging");
SYSCTL_U16(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, "");
SYSCTL_U16(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, "");
static struct lock_delay_config __read_frequently rw_delay;
SYSCTL_U16(_debug_rwlock, OID_AUTO, delay_base, CTLFLAG_RW, &rw_delay.base,
0, "");
SYSCTL_U16(_debug_rwlock, OID_AUTO, delay_max, CTLFLAG_RW, &rw_delay.max,
0, "");
static void
rw_lock_delay_init(void *arg __unused)
{
lock_delay_default_init(&rw_delay);
rowner_retries = 10;
rowner_loops = max(10000, rw_delay.max);
}
LOCK_DELAY_SYSINIT(rw_lock_delay_init);
#else
#define rw_delay locks_delay
#define rowner_retries locks_delay_retries
#define rowner_loops locks_delay_loops
#endif
#endif
/*
* Return a pointer to the owning thread if the lock is write-locked or
* NULL if the lock is unlocked or read-locked.
*/
#define lv_rw_wowner(v) \
((v) & RW_LOCK_READ ? NULL : \
(struct thread *)RW_OWNER((v)))
#define rw_wowner(rw) lv_rw_wowner(RW_READ_VALUE(rw))
/*
* Returns if a write owner is recursed. Write ownership is not assured
* here and should be previously checked.
*/
#define rw_recursed(rw) ((rw)->rw_recurse != 0)
/*
* Return true if curthread helds the lock.
*/
#define rw_wlocked(rw) (rw_wowner((rw)) == curthread)
/*
* Return a pointer to the owning thread for this lock who should receive
* any priority lent by threads that block on this lock. Currently this
* is identical to rw_wowner().
*/
#define rw_owner(rw) rw_wowner(rw)
#ifndef INVARIANTS
#define __rw_assert(c, what, file, line)
#endif
void
assert_rw(const struct lock_object *lock, int what)
{
rw_assert((const struct rwlock *)lock, what);
}
void
lock_rw(struct lock_object *lock, uintptr_t how)
{
struct rwlock *rw;
rw = (struct rwlock *)lock;
if (how)
rw_rlock(rw);
else
rw_wlock(rw);
}
uintptr_t
unlock_rw(struct lock_object *lock)
{
struct rwlock *rw;
rw = (struct rwlock *)lock;
rw_assert(rw, RA_LOCKED | LA_NOTRECURSED);
if (rw->rw_lock & RW_LOCK_READ) {
rw_runlock(rw);
return (1);
} else {
rw_wunlock(rw);
return (0);
}
}
#ifdef KDTRACE_HOOKS
int
owner_rw(const struct lock_object *lock, struct thread **owner)
{
const struct rwlock *rw = (const struct rwlock *)lock;
uintptr_t x = rw->rw_lock;
*owner = rw_wowner(rw);
return ((x & RW_LOCK_READ) != 0 ? (RW_READERS(x) != 0) :
(*owner != NULL));
}
#endif
void
_rw_init_flags(volatile uintptr_t *c, const char *name, int opts)
{
struct rwlock *rw;
int flags;
rw = rwlock2rw(c);
MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET |
RW_RECURSE | RW_NEW)) == 0);
ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock,
("%s: rw_lock not aligned for %s: %p", __func__, name,
&rw->rw_lock));
flags = LO_UPGRADABLE;
if (opts & RW_DUPOK)
flags |= LO_DUPOK;
if (opts & RW_NOPROFILE)
flags |= LO_NOPROFILE;
if (!(opts & RW_NOWITNESS))
flags |= LO_WITNESS;
if (opts & RW_RECURSE)
flags |= LO_RECURSABLE;
if (opts & RW_QUIET)
flags |= LO_QUIET;
if (opts & RW_NEW)
flags |= LO_NEW;
lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags);
rw->rw_lock = RW_UNLOCKED;
rw->rw_recurse = 0;
}
void
_rw_destroy(volatile uintptr_t *c)
{
struct rwlock *rw;
rw = rwlock2rw(c);
KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw));
KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw));
rw->rw_lock = RW_DESTROYED;
lock_destroy(&rw->lock_object);
}
void
rw_sysinit(void *arg)
{
struct rw_args *args;
args = arg;
rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc,
args->ra_flags);
}
int
_rw_wowned(const volatile uintptr_t *c)
{
return (rw_wowner(rwlock2rw(c)) == curthread);
}
void
_rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line)
{
struct rwlock *rw;
uintptr_t tid, v;
rw = rwlock2rw(c);
KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
!TD_IS_IDLETHREAD(curthread),
("rw_wlock() by idle thread %p on rwlock %s @ %s:%d",
curthread, rw->lock_object.lo_name, file, line));
KASSERT(rw->rw_lock != RW_DESTROYED,
("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
line, NULL);
tid = (uintptr_t)curthread;
v = RW_UNLOCKED;
if (!_rw_write_lock_fetch(rw, &v, tid))
_rw_wlock_hard(rw, v, file, line);
else
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw,
0, 0, file, line, LOCKSTAT_WRITER);
LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line);
WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
TD_LOCKS_INC(curthread);
}
int
__rw_try_wlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
{
struct thread *td;
uintptr_t tid, v;
int rval;
bool recursed;
td = curthread;
tid = (uintptr_t)td;
if (SCHEDULER_STOPPED_TD(td))
return (1);
KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d",
curthread, rw->lock_object.lo_name, file, line));
KASSERT(rw->rw_lock != RW_DESTROYED,
("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
rval = 1;
recursed = false;
v = RW_UNLOCKED;
for (;;) {
if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
break;
if (v == RW_UNLOCKED)
continue;
if (v == tid && (rw->lock_object.lo_flags & LO_RECURSABLE)) {
rw->rw_recurse++;
atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
break;
}
rval = 0;
break;
}
LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);
if (rval) {
WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
file, line);
if (!recursed)
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
rw, 0, 0, file, line, LOCKSTAT_WRITER);
TD_LOCKS_INC(curthread);
}
return (rval);
}
int
__rw_try_wlock(volatile uintptr_t *c, const char *file, int line)
{
struct rwlock *rw;
rw = rwlock2rw(c);
return (__rw_try_wlock_int(rw LOCK_FILE_LINE_ARG));
}
void
_rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
{
struct rwlock *rw;
rw = rwlock2rw(c);
KASSERT(rw->rw_lock != RW_DESTROYED,
("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
__rw_assert(c, RA_WLOCKED, file, line);
WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
line);
#ifdef LOCK_PROFILING
_rw_wunlock_hard(rw, (uintptr_t)curthread, file, line);
#else
__rw_wunlock(rw, curthread, file, line);
#endif
TD_LOCKS_DEC(curthread);
}
/*
* Determines whether a new reader can acquire a lock. Succeeds if the
* reader already owns a read lock and the lock is locked for read to
* prevent deadlock from reader recursion. Also succeeds if the lock
* is unlocked and has no writer waiters or spinners. Failing otherwise
* prioritizes writers before readers.
*/
static bool __always_inline
__rw_can_read(struct thread *td, uintptr_t v, bool fp)
{
if ((v & (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER))
== RW_LOCK_READ)
return (true);
if (!fp && td->td_rw_rlocks && (v & RW_LOCK_READ))
return (true);
return (false);
}
static bool __always_inline
__rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp, bool fp
LOCK_FILE_LINE_ARG_DEF)
{
/*
* Handle the easy case. If no other thread has a write
* lock, then try to bump up the count of read locks. Note
* that we have to preserve the current state of the
* RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a
* read lock, then rw_lock must have changed, so restart
* the loop. Note that this handles the case of a
* completely unlocked rwlock since such a lock is encoded
* as a read lock with no waiters.
*/
while (__rw_can_read(td, *vp, fp)) {
if (atomic_fcmpset_acq_ptr(&rw->rw_lock, vp,
*vp + RW_ONE_READER)) {
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR4(KTR_LOCK,
"%s: %p succeed %p -> %p", __func__,
rw, (void *)*vp,
(void *)(*vp + RW_ONE_READER));
td->td_rw_rlocks++;
return (true);
}
}
return (false);
}
static void __noinline
__rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
LOCK_FILE_LINE_ARG_DEF)
{
struct turnstile *ts;
struct thread *owner;
#ifdef ADAPTIVE_RWLOCKS
int spintries = 0;
int i, n;
#endif
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
int contested = 0;
#endif
#if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
struct lock_delay_arg lda;
#endif
#ifdef KDTRACE_HOOKS
u_int sleep_cnt = 0;
int64_t sleep_time = 0;
int64_t all_time = 0;
#endif
#if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
uintptr_t state = 0;
int doing_lockprof = 0;
#endif
#ifdef KDTRACE_HOOKS
if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
goto out_lockstat;
doing_lockprof = 1;
all_time -= lockstat_nsecs(&rw->lock_object);
state = v;
}
#endif
#ifdef LOCK_PROFILING
doing_lockprof = 1;
state = v;
#endif
if (SCHEDULER_STOPPED())
return;
#if defined(ADAPTIVE_RWLOCKS)
lock_delay_arg_init(&lda, &rw_delay);
#elif defined(KDTRACE_HOOKS)
lock_delay_arg_init_noadapt(&lda);
#endif
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&rw->lock_object, false,
&contested, &waittime);
for (;;) {
if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
break;
#ifdef KDTRACE_HOOKS
lda.spin_cnt++;
#endif
#ifdef ADAPTIVE_RWLOCKS
/*
* If the owner is running on another CPU, spin until
* the owner stops running or the state of the lock
* changes.
*/
if ((v & RW_LOCK_READ) == 0) {
owner = (struct thread *)RW_OWNER(v);
if (TD_IS_RUNNING(owner)) {
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR3(KTR_LOCK,
"%s: spinning on %p held by %p",
__func__, rw, owner);
KTR_STATE1(KTR_SCHED, "thread",
sched_tdname(curthread), "spinning",
"lockname:\"%s\"", rw->lock_object.lo_name);
do {
lock_delay(&lda);
v = RW_READ_VALUE(rw);
owner = lv_rw_wowner(v);
} while (owner != NULL && TD_IS_RUNNING(owner));
KTR_STATE0(KTR_SCHED, "thread",
sched_tdname(curthread), "running");
continue;
}
} else {
if ((v & RW_LOCK_WRITE_SPINNER) && RW_READERS(v) == 0) {
MPASS(!__rw_can_read(td, v, false));
lock_delay_spin(2);
v = RW_READ_VALUE(rw);
continue;
}
if (spintries < rowner_retries) {
spintries++;
KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
"spinning", "lockname:\"%s\"",
rw->lock_object.lo_name);
n = RW_READERS(v);
for (i = 0; i < rowner_loops; i += n) {
lock_delay_spin(n);
v = RW_READ_VALUE(rw);
if (!(v & RW_LOCK_READ))
break;
n = RW_READERS(v);
if (n == 0)
break;
if (__rw_can_read(td, v, false))
break;
}
#ifdef KDTRACE_HOOKS
lda.spin_cnt += rowner_loops - i;
#endif
KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
"running");
if (i < rowner_loops)
continue;
}
}
#endif
/*
* Okay, now it's the hard case. Some other thread already
* has a write lock or there are write waiters present,
* acquire the turnstile lock so we can begin the process
* of blocking.
*/
ts = turnstile_trywait(&rw->lock_object);
/*
* The lock might have been released while we spun, so
* recheck its state and restart the loop if needed.
*/
v = RW_READ_VALUE(rw);
retry_ts:
if (((v & RW_LOCK_WRITE_SPINNER) && RW_READERS(v) == 0) ||
__rw_can_read(td, v, false)) {
turnstile_cancel(ts);
continue;
}
owner = lv_rw_wowner(v);
#ifdef ADAPTIVE_RWLOCKS
/*
* The current lock owner might have started executing
* on another CPU (or the lock could have changed
* owners) while we were waiting on the turnstile
* chain lock. If so, drop the turnstile lock and try
* again.
*/
if (owner != NULL) {
if (TD_IS_RUNNING(owner)) {
turnstile_cancel(ts);
continue;
}
}
#endif
/*
* The lock is held in write mode or it already has waiters.
*/
MPASS(!__rw_can_read(td, v, false));
/*
* If the RW_LOCK_READ_WAITERS flag is already set, then
* we can go ahead and block. If it is not set then try
* to set it. If we fail to set it drop the turnstile
* lock and restart the loop.
*/
if (!(v & RW_LOCK_READ_WAITERS)) {
if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
v | RW_LOCK_READ_WAITERS))
goto retry_ts;
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p set read waiters flag",
__func__, rw);
}
/*
* We were unable to acquire the lock and the read waiters
* flag is set, so we must block on the turnstile.
*/
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
rw);
#ifdef KDTRACE_HOOKS
sleep_time -= lockstat_nsecs(&rw->lock_object);
#endif
MPASS(owner == rw_owner(rw));
turnstile_wait(ts, owner, TS_SHARED_QUEUE);
#ifdef KDTRACE_HOOKS
sleep_time += lockstat_nsecs(&rw->lock_object);
sleep_cnt++;
#endif
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
__func__, rw);
v = RW_READ_VALUE(rw);
}
#if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
if (__predict_true(!doing_lockprof))
return;
#endif
#ifdef KDTRACE_HOOKS
all_time += lockstat_nsecs(&rw->lock_object);
if (sleep_time)
LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
(state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
/* Record only the loops spinning and not sleeping. */
if (lda.spin_cnt > sleep_cnt)
LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
(state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
out_lockstat:
#endif
/*
* TODO: acquire "owner of record" here. Here be turnstile dragons
* however. turnstiles don't like owners changing between calls to
* turnstile_wait() currently.
*/
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
waittime, file, line, LOCKSTAT_READER);
}
void
__rw_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
{
struct thread *td;
uintptr_t v;
td = curthread;
KASSERT(kdb_active != 0 || SCHEDULER_STOPPED_TD(td) ||
!TD_IS_IDLETHREAD(td),
("rw_rlock() by idle thread %p on rwlock %s @ %s:%d",
td, rw->lock_object.lo_name, file, line));
KASSERT(rw->rw_lock != RW_DESTROYED,
("rw_rlock() of destroyed rwlock @ %s:%d", file, line));
KASSERT(rw_wowner(rw) != td,
("rw_rlock: wlock already held for %s @ %s:%d",
rw->lock_object.lo_name, file, line));
WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL);
v = RW_READ_VALUE(rw);
if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__acquire) ||
!__rw_rlock_try(rw, td, &v, true LOCK_FILE_LINE_ARG)))
__rw_rlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
else
lock_profile_obtain_lock_success(&rw->lock_object, false, 0, 0,
file, line);
LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
WITNESS_LOCK(&rw->lock_object, 0, file, line);
TD_LOCKS_INC(curthread);
}
void
__rw_rlock(volatile uintptr_t *c, const char *file, int line)
{
struct rwlock *rw;
rw = rwlock2rw(c);
__rw_rlock_int(rw LOCK_FILE_LINE_ARG);
}
int
__rw_try_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
{
uintptr_t x;
if (SCHEDULER_STOPPED())
return (1);
KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d",
curthread, rw->lock_object.lo_name, file, line));
x = rw->rw_lock;
for (;;) {
KASSERT(rw->rw_lock != RW_DESTROYED,
("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line));
if (!(x & RW_LOCK_READ))
break;
if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &x, x + RW_ONE_READER)) {
LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file,
line);
WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line);
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
rw, 0, 0, file, line, LOCKSTAT_READER);
TD_LOCKS_INC(curthread);
curthread->td_rw_rlocks++;
return (1);
}
}
LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line);
return (0);
}
int
__rw_try_rlock(volatile uintptr_t *c, const char *file, int line)
{
struct rwlock *rw;
rw = rwlock2rw(c);
return (__rw_try_rlock_int(rw LOCK_FILE_LINE_ARG));
}
static bool __always_inline
__rw_runlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp)
{
for (;;) {
if (RW_READERS(*vp) > 1 || !(*vp & RW_LOCK_WAITERS)) {
if (atomic_fcmpset_rel_ptr(&rw->rw_lock, vp,
*vp - RW_ONE_READER)) {
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR4(KTR_LOCK,
"%s: %p succeeded %p -> %p",
__func__, rw, (void *)*vp,
(void *)(*vp - RW_ONE_READER));
td->td_rw_rlocks--;
return (true);
}
continue;
}
break;
}
return (false);
}
static void __noinline
__rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
LOCK_FILE_LINE_ARG_DEF)
{
struct turnstile *ts;
uintptr_t setv, queue;
if (SCHEDULER_STOPPED())
return;
if (__rw_runlock_try(rw, td, &v))
goto out_lockstat;
/*
* Ok, we know we have waiters and we think we are the
* last reader, so grab the turnstile lock.
*/
turnstile_chain_lock(&rw->lock_object);
v = RW_READ_VALUE(rw);
for (;;) {
if (__rw_runlock_try(rw, td, &v))
break;
MPASS(v & RW_LOCK_WAITERS);
/*
* Try to drop our lock leaving the lock in a unlocked
* state.
*
* If you wanted to do explicit lock handoff you'd have to
* do it here. You'd also want to use turnstile_signal()
* and you'd have to handle the race where a higher
* priority thread blocks on the write lock before the
* thread you wakeup actually runs and have the new thread
* "steal" the lock. For now it's a lot simpler to just
* wakeup all of the waiters.
*
* As above, if we fail, then another thread might have
* acquired a read lock, so drop the turnstile lock and
* restart.
*/
setv = RW_UNLOCKED;
queue = TS_SHARED_QUEUE;
if (v & RW_LOCK_WRITE_WAITERS) {
queue = TS_EXCLUSIVE_QUEUE;
setv |= (v & RW_LOCK_READ_WAITERS);
}
setv |= (v & RW_LOCK_WRITE_SPINNER);
if (!atomic_fcmpset_rel_ptr(&rw->rw_lock, &v, setv))
continue;
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
__func__, rw);
/*
* Ok. The lock is released and all that's left is to
* wake up the waiters. Note that the lock might not be
* free anymore, but in that case the writers will just
* block again if they run before the new lock holder(s)
* release the lock.
*/
ts = turnstile_lookup(&rw->lock_object);
MPASS(ts != NULL);
turnstile_broadcast(ts, queue);
turnstile_unpend(ts);
td->td_rw_rlocks--;
break;
}
turnstile_chain_unlock(&rw->lock_object);
out_lockstat:
LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_READER);
}
void
_rw_runlock_cookie_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
{
struct thread *td;
uintptr_t v;
KASSERT(rw->rw_lock != RW_DESTROYED,
("rw_runlock() of destroyed rwlock @ %s:%d", file, line));
__rw_assert(&rw->rw_lock, RA_RLOCKED, file, line);
WITNESS_UNLOCK(&rw->lock_object, 0, file, line);
LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line);
td = curthread;
v = RW_READ_VALUE(rw);
if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__release) ||
!__rw_runlock_try(rw, td, &v)))
__rw_runlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
else
lock_profile_release_lock(&rw->lock_object, false);
TD_LOCKS_DEC(curthread);
}
void
_rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line)
{
struct rwlock *rw;
rw = rwlock2rw(c);
_rw_runlock_cookie_int(rw LOCK_FILE_LINE_ARG);
}
#ifdef ADAPTIVE_RWLOCKS
static inline void
rw_drop_critical(uintptr_t v, bool *in_critical, int *extra_work)
{
if (v & RW_LOCK_WRITE_SPINNER)
return;
if (*in_critical) {
critical_exit();
*in_critical = false;
(*extra_work)--;
}
}
#else
#define rw_drop_critical(v, in_critical, extra_work) do { } while (0)
#endif
/*
* This function is called when we are unable to obtain a write lock on the
* first try. This means that at least one other thread holds either a
* read or write lock.
*/
void
__rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
{
uintptr_t tid;
struct rwlock *rw;
struct turnstile *ts;
struct thread *owner;
#ifdef ADAPTIVE_RWLOCKS
int spintries = 0;
int i, n;
enum { READERS, WRITER } sleep_reason = READERS;
bool in_critical = false;
#endif
uintptr_t setv;
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
int contested = 0;
#endif
#if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
struct lock_delay_arg lda;
#endif
#ifdef KDTRACE_HOOKS
u_int sleep_cnt = 0;
int64_t sleep_time = 0;
int64_t all_time = 0;
#endif
#if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
uintptr_t state = 0;
int doing_lockprof = 0;
#endif
int extra_work = 0;
tid = (uintptr_t)curthread;
rw = rwlock2rw(c);
#ifdef KDTRACE_HOOKS
if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
while (v == RW_UNLOCKED) {
if (_rw_write_lock_fetch(rw, &v, tid))
goto out_lockstat;
}
extra_work = 1;
doing_lockprof = 1;
all_time -= lockstat_nsecs(&rw->lock_object);
state = v;
}
#endif
#ifdef LOCK_PROFILING
extra_work = 1;
doing_lockprof = 1;
state = v;
#endif
if (SCHEDULER_STOPPED())
return;
if (__predict_false(v == RW_UNLOCKED))
v = RW_READ_VALUE(rw);
if (__predict_false(lv_rw_wowner(v) == (struct thread *)tid)) {
KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE,
("%s: recursing but non-recursive rw %s @ %s:%d\n",
__func__, rw->lock_object.lo_name, file, line));
rw->rw_recurse++;
atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw);
return;
}
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
rw->lock_object.lo_name, (void *)rw->rw_lock, file, line);
#if defined(ADAPTIVE_RWLOCKS)
lock_delay_arg_init(&lda, &rw_delay);
#elif defined(KDTRACE_HOOKS)
lock_delay_arg_init_noadapt(&lda);
#endif
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&rw->lock_object, false,
&contested, &waittime);
for (;;) {
if (v == RW_UNLOCKED) {
if (_rw_write_lock_fetch(rw, &v, tid))
break;
continue;
}
#ifdef KDTRACE_HOOKS
lda.spin_cnt++;
#endif
#ifdef ADAPTIVE_RWLOCKS
if (v == (RW_LOCK_READ | RW_LOCK_WRITE_SPINNER)) {
if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
break;
continue;
}
/*
* If the lock is write locked and the owner is
* running on another CPU, spin until the owner stops
* running or the state of the lock changes.
*/
if (!(v & RW_LOCK_READ)) {
rw_drop_critical(v, &in_critical, &extra_work);
sleep_reason = WRITER;
owner = lv_rw_wowner(v);
if (!TD_IS_RUNNING(owner))
goto ts;
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
__func__, rw, owner);
KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
"spinning", "lockname:\"%s\"",
rw->lock_object.lo_name);
do {
lock_delay(&lda);
v = RW_READ_VALUE(rw);
owner = lv_rw_wowner(v);
} while (owner != NULL && TD_IS_RUNNING(owner));
KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
"running");
continue;
} else if (RW_READERS(v) > 0) {
sleep_reason = READERS;
if (spintries == rowner_retries)
goto ts;
if (!(v & RW_LOCK_WRITE_SPINNER)) {
if (!in_critical) {
critical_enter();
in_critical = true;
extra_work++;
}
if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
v | RW_LOCK_WRITE_SPINNER)) {
critical_exit();
in_critical = false;
extra_work--;
continue;
}
}
spintries++;
KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
"spinning", "lockname:\"%s\"",
rw->lock_object.lo_name);
n = RW_READERS(v);
for (i = 0; i < rowner_loops; i += n) {
lock_delay_spin(n);
v = RW_READ_VALUE(rw);
if (!(v & RW_LOCK_WRITE_SPINNER))
break;
if (!(v & RW_LOCK_READ))
break;
n = RW_READERS(v);
if (n == 0)
break;
}
#ifdef KDTRACE_HOOKS
lda.spin_cnt += i;
#endif
KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
"running");
if (i < rowner_loops)
continue;
}
ts:
#endif
ts = turnstile_trywait(&rw->lock_object);
v = RW_READ_VALUE(rw);
retry_ts:
owner = lv_rw_wowner(v);
#ifdef ADAPTIVE_RWLOCKS
/*
* The current lock owner might have started executing
* on another CPU (or the lock could have changed
* owners) while we were waiting on the turnstile
* chain lock. If so, drop the turnstile lock and try
* again.
*/
if (owner != NULL) {
if (TD_IS_RUNNING(owner)) {
turnstile_cancel(ts);
rw_drop_critical(v, &in_critical, &extra_work);
continue;
}
} else if (RW_READERS(v) > 0 && sleep_reason == WRITER) {
turnstile_cancel(ts);
rw_drop_critical(v, &in_critical, &extra_work);
continue;
}
#endif
/*
* Check for the waiters flags about this rwlock.
* If the lock was released, without maintain any pending
* waiters queue, simply try to acquire it.
* If a pending waiters queue is present, claim the lock
* ownership and maintain the pending queue.
*/
setv = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
if ((v & ~setv) == RW_UNLOCKED) {
setv &= ~RW_LOCK_WRITE_SPINNER;
if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid | setv)) {
if (setv)
turnstile_claim(ts);
else
turnstile_cancel(ts);
break;
}
goto retry_ts;
}
#ifdef ADAPTIVE_RWLOCKS
if (in_critical) {
if ((v & RW_LOCK_WRITE_SPINNER) ||
!((v & RW_LOCK_WRITE_WAITERS))) {
setv = v & ~RW_LOCK_WRITE_SPINNER;
setv |= RW_LOCK_WRITE_WAITERS;
if (!atomic_fcmpset_ptr(&rw->rw_lock, &v, setv))
goto retry_ts;
}
critical_exit();
in_critical = false;
extra_work--;
} else {
#endif
/*
* If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
* set it. If we fail to set it, then loop back and try
* again.
*/
if (!(v & RW_LOCK_WRITE_WAITERS)) {
if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
v | RW_LOCK_WRITE_WAITERS))
goto retry_ts;
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p set write waiters flag",
__func__, rw);
}
#ifdef ADAPTIVE_RWLOCKS
}
#endif
/*
* We were unable to acquire the lock and the write waiters
* flag is set, so we must block on the turnstile.
*/
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
rw);
#ifdef KDTRACE_HOOKS
sleep_time -= lockstat_nsecs(&rw->lock_object);
#endif
MPASS(owner == rw_owner(rw));
turnstile_wait(ts, owner, TS_EXCLUSIVE_QUEUE);
#ifdef KDTRACE_HOOKS
sleep_time += lockstat_nsecs(&rw->lock_object);
sleep_cnt++;
#endif
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
__func__, rw);
#ifdef ADAPTIVE_RWLOCKS
spintries = 0;
#endif
v = RW_READ_VALUE(rw);
}
if (__predict_true(!extra_work))
return;
#ifdef ADAPTIVE_RWLOCKS
if (in_critical)
critical_exit();
#endif
#if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
if (__predict_true(!doing_lockprof))
return;
#endif
#ifdef KDTRACE_HOOKS
all_time += lockstat_nsecs(&rw->lock_object);
if (sleep_time)
LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
(state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
/* Record only the loops spinning and not sleeping. */
if (lda.spin_cnt > sleep_cnt)
LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
(state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
out_lockstat:
#endif
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
waittime, file, line, LOCKSTAT_WRITER);
}
/*
* This function is called if lockstat is active or the first try at releasing
* a write lock failed. The latter means that the lock is recursed or one of
* the 2 waiter bits must be set indicating that at least one thread is waiting
* on this lock.
*/
void
__rw_wunlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
{
struct rwlock *rw;
struct turnstile *ts;
uintptr_t tid, setv;
int queue;
tid = (uintptr_t)curthread;
if (SCHEDULER_STOPPED())
return;
rw = rwlock2rw(c);
if (__predict_false(v == tid))
v = RW_READ_VALUE(rw);
if (v & RW_LOCK_WRITER_RECURSED) {
if (--(rw->rw_recurse) == 0)
atomic_clear_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
return;
}
LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_WRITER);
if (v == tid && _rw_write_unlock(rw, tid))
return;
KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
("%s: neither of the waiter flags are set", __func__));
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
turnstile_chain_lock(&rw->lock_object);
/*
* Use the same algo as sx locks for now. Prefer waking up shared
* waiters if we have any over writers. This is probably not ideal.
*
* 'v' is the value we are going to write back to rw_lock. If we
* have waiters on both queues, we need to preserve the state of
* the waiter flag for the queue we don't wake up. For now this is
* hardcoded for the algorithm mentioned above.
*
* In the case of both readers and writers waiting we wakeup the
* readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a
* new writer comes in before a reader it will claim the lock up
* above. There is probably a potential priority inversion in
* there that could be worked around either by waking both queues
* of waiters or doing some complicated lock handoff gymnastics.
*/
setv = RW_UNLOCKED;
v = RW_READ_VALUE(rw);
queue = TS_SHARED_QUEUE;
if (v & RW_LOCK_WRITE_WAITERS) {
queue = TS_EXCLUSIVE_QUEUE;
setv |= (v & RW_LOCK_READ_WAITERS);
}
atomic_store_rel_ptr(&rw->rw_lock, setv);
/* Wake up all waiters for the specific queue. */
if (LOCK_LOG_TEST(&rw->lock_object, 0))
CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
queue == TS_SHARED_QUEUE ? "read" : "write");
ts = turnstile_lookup(&rw->lock_object);
MPASS(ts != NULL);
turnstile_broadcast(ts, queue);
turnstile_unpend(ts);
turnstile_chain_unlock(&rw->lock_object);
}
/*
* Attempt to do a non-blocking upgrade from a read lock to a write
* lock. This will only succeed if this thread holds a single read
* lock. Returns true if the upgrade succeeded and false otherwise.
*/
int
__rw_try_upgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
{
uintptr_t v, setv, tid;
struct turnstile *ts;
int success;
if (SCHEDULER_STOPPED())
return (1);
KASSERT(rw->rw_lock != RW_DESTROYED,
("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line));
__rw_assert(&rw->rw_lock, RA_RLOCKED, file, line);
/*
* Attempt to switch from one reader to a writer. If there
* are any write waiters, then we will have to lock the
* turnstile first to prevent races with another writer
* calling turnstile_wait() before we have claimed this
* turnstile. So, do the simple case of no waiters first.
*/
tid = (uintptr_t)curthread;
success = 0;
v = RW_READ_VALUE(rw);
for (;;) {
if (RW_READERS(v) > 1)
break;
if (!(v & RW_LOCK_WAITERS)) {
success = atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid);
if (!success)
continue;
break;
}
/*
* Ok, we think we have waiters, so lock the turnstile.
*/
ts = turnstile_trywait(&rw->lock_object);
v = RW_READ_VALUE(rw);
retry_ts:
if (RW_READERS(v) > 1) {
turnstile_cancel(ts);
break;
}
/*
* Try to switch from one reader to a writer again. This time
* we honor the current state of the waiters flags.
* If we obtain the lock with the flags set, then claim
* ownership of the turnstile.
*/
setv = tid | (v & RW_LOCK_WAITERS);
success = atomic_fcmpset_ptr(&rw->rw_lock, &v, setv);
if (success) {
if (v & RW_LOCK_WAITERS)
turnstile_claim(ts);
else
turnstile_cancel(ts);
break;
}
goto retry_ts;
}
LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line);
if (success) {
curthread->td_rw_rlocks--;
WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
file, line);
LOCKSTAT_RECORD0(rw__upgrade, rw);
}
return (success);
}
int
__rw_try_upgrade(volatile uintptr_t *c, const char *file, int line)
{
struct rwlock *rw;
rw = rwlock2rw(c);
return (__rw_try_upgrade_int(rw LOCK_FILE_LINE_ARG));
}
/*
* Downgrade a write lock into a single read lock.
*/
void
__rw_downgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
{
struct turnstile *ts;
uintptr_t tid, v;
int rwait, wwait;
if (SCHEDULER_STOPPED())
return;
KASSERT(rw->rw_lock != RW_DESTROYED,
("rw_downgrade() of destroyed rwlock @ %s:%d", file, line));
__rw_assert(&rw->rw_lock, RA_WLOCKED | RA_NOTRECURSED, file, line);
#ifndef INVARIANTS
if (rw_recursed(rw))
panic("downgrade of a recursed lock");
#endif
WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line);
/*
* Convert from a writer to a single reader. First we handle
* the easy case with no waiters. If there are any waiters, we
* lock the turnstile and "disown" the lock.
*/
tid = (uintptr_t)curthread;
if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1)))
goto out;
/*
* Ok, we think we have waiters, so lock the turnstile so we can
* read the waiter flags without any races.
*/
turnstile_chain_lock(&rw->lock_object);
v = rw->rw_lock & RW_LOCK_WAITERS;
rwait = v & RW_LOCK_READ_WAITERS;
wwait = v & RW_LOCK_WRITE_WAITERS;
MPASS(rwait | wwait);
/*
* Downgrade from a write lock while preserving waiters flag
* and give up ownership of the turnstile.
*/
ts = turnstile_lookup(&rw->lock_object);
MPASS(ts != NULL);
if (!wwait)
v &= ~RW_LOCK_READ_WAITERS;
atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v);
/*
* Wake other readers if there are no writers pending. Otherwise they
* won't be able to acquire the lock anyway.
*/
if (rwait && !wwait) {
turnstile_broadcast(ts, TS_SHARED_QUEUE);
turnstile_unpend(ts);
} else
turnstile_disown(ts);
turnstile_chain_unlock(&rw->lock_object);
out:
curthread->td_rw_rlocks++;
LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line);
LOCKSTAT_RECORD0(rw__downgrade, rw);
}
void
__rw_downgrade(volatile uintptr_t *c, const char *file, int line)
{
struct rwlock *rw;
rw = rwlock2rw(c);
__rw_downgrade_int(rw LOCK_FILE_LINE_ARG);
}
#ifdef INVARIANT_SUPPORT
#ifndef INVARIANTS
#undef __rw_assert
#endif
/*
* In the non-WITNESS case, rw_assert() can only detect that at least
* *some* thread owns an rlock, but it cannot guarantee that *this*
* thread owns an rlock.
*/
void
__rw_assert(const volatile uintptr_t *c, int what, const char *file, int line)
{
const struct rwlock *rw;
if (SCHEDULER_STOPPED())
return;
rw = rwlock2rw(c);
switch (what) {
case RA_LOCKED:
case RA_LOCKED | RA_RECURSED:
case RA_LOCKED | RA_NOTRECURSED:
case RA_RLOCKED:
case RA_RLOCKED | RA_RECURSED:
case RA_RLOCKED | RA_NOTRECURSED:
#ifdef WITNESS
witness_assert(&rw->lock_object, what, file, line);
#else
/*
* If some other thread has a write lock or we have one
* and are asserting a read lock, fail. Also, if no one
* has a lock at all, fail.
*/
if (rw->rw_lock == RW_UNLOCKED ||
(!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED ||
rw_wowner(rw) != curthread)))
panic("Lock %s not %slocked @ %s:%d\n",
rw->lock_object.lo_name, (what & RA_RLOCKED) ?
"read " : "", file, line);
if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) {
if (rw_recursed(rw)) {
if (what & RA_NOTRECURSED)
panic("Lock %s recursed @ %s:%d\n",
rw->lock_object.lo_name, file,
line);
} else if (what & RA_RECURSED)
panic("Lock %s not recursed @ %s:%d\n",
rw->lock_object.lo_name, file, line);
}
#endif
break;
case RA_WLOCKED:
case RA_WLOCKED | RA_RECURSED:
case RA_WLOCKED | RA_NOTRECURSED:
if (rw_wowner(rw) != curthread)
panic("Lock %s not exclusively locked @ %s:%d\n",
rw->lock_object.lo_name, file, line);
if (rw_recursed(rw)) {
if (what & RA_NOTRECURSED)
panic("Lock %s recursed @ %s:%d\n",
rw->lock_object.lo_name, file, line);
} else if (what & RA_RECURSED)
panic("Lock %s not recursed @ %s:%d\n",
rw->lock_object.lo_name, file, line);
break;
case RA_UNLOCKED:
#ifdef WITNESS
witness_assert(&rw->lock_object, what, file, line);
#else
/*
* If we hold a write lock fail. We can't reliably check
* to see if we hold a read lock or not.
*/
if (rw_wowner(rw) == curthread)
panic("Lock %s exclusively locked @ %s:%d\n",
rw->lock_object.lo_name, file, line);
#endif
break;
default:
panic("Unknown rw lock assertion: %d @ %s:%d", what, file,
line);
}
}
#endif /* INVARIANT_SUPPORT */
#ifdef DDB
void
db_show_rwlock(const struct lock_object *lock)
{
const struct rwlock *rw;
struct thread *td;
rw = (const struct rwlock *)lock;
db_printf(" state: ");
if (rw->rw_lock == RW_UNLOCKED)
db_printf("UNLOCKED\n");
else if (rw->rw_lock == RW_DESTROYED) {
db_printf("DESTROYED\n");
return;
} else if (rw->rw_lock & RW_LOCK_READ)
db_printf("RLOCK: %ju locks\n",
(uintmax_t)(RW_READERS(rw->rw_lock)));
else {
td = rw_wowner(rw);
db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
td->td_tid, td->td_proc->p_pid, td->td_name);
if (rw_recursed(rw))
db_printf(" recursed: %u\n", rw->rw_recurse);
}
db_printf(" waiters: ");
switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) {
case RW_LOCK_READ_WAITERS:
db_printf("readers\n");
break;
case RW_LOCK_WRITE_WAITERS:
db_printf("writers\n");
break;
case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS:
db_printf("readers and writers\n");
break;
default:
db_printf("none\n");
break;
}
}
#endif
