freebsd-dev/sys/kern/kern_rwlock.c
Mateusz Guzik 9feec7ef69 rw: decrease writer starvation
Writers waiting on readers to finish can set the RW_LOCK_WRITE_SPINNER
bit. This prevents most new readers from coming on. However, the last
reader to unlock also clears the bit which means new readers can sneak
in and the cycle starts over.

Change the code to keep the bit after last unlock.

Note that starvation potential is still there: no matter how many write
spinners are there, there is one bit. After the writer unlocks, the lock
is free to get raided by readers again. It is good enough for the time
being.

The real fix would include counting writers.

This runs into a caveat: the writer which set the bit may now be preempted.
In order to get rid of the problem all attempts to set the bit are preceeded
with critical_enter.

The bit gets cleared when the thread which set it goes to sleep. This way
an invariant holds that if the bit is set, someone is actively spinning and
will grab the lock soon. In particular this means that readers which find
the lock in this transient state can safely spin until the lock finds itself
an owner (i.e. they don't need to block nor speculate how long to spin
speculatively).

Tested by:	pho
2018-05-22 07:16:39 +00:00

1558 lines
41 KiB
C

/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2006 John Baldwin <jhb@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, 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
static int __read_frequently rowner_retries;
static int __read_frequently rowner_loops;
static SYSCTL_NODE(_debug, OID_AUTO, rwlock, CTLFLAG_RD, NULL,
"rwlock debugging");
SYSCTL_INT(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, "");
SYSCTL_INT(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, "");
static struct lock_delay_config __read_frequently rw_delay;
SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_base, CTLFLAG_RW, &rw_delay.base,
0, "");
SYSCTL_INT(_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);
#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;
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(&lda, NULL);
#endif
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&rw->lock_object,
&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, 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, TS_SHARED_LOCK);
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);
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;
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 defined(ADAPTIVE_RWLOCKS)
lock_delay_arg_init(&lda, &rw_delay);
#elif defined(KDTRACE_HOOKS)
lock_delay_arg_init(&lda, NULL);
#endif
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);
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&rw->lock_object,
&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, TS_EXCLUSIVE_LOCK);
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, TS_EXCLUSIVE_LOCK);
} 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 (panicstr != NULL)
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