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freebsd-nq/sys/kern/kern_lock.c

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/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2008 Attilio Rao <attilio@FreeBSD.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice(s), this list of conditions and the following disclaimer as
* the first lines of this file unmodified other than the possible
* addition of one or more copyright notices.
* 2. Redistributions in binary form must reproduce the above copyright
* notice(s), this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGE.
*/
#include "opt_ddb.h"
#include "opt_hwpmc_hooks.h"
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/kdb.h>
#include <sys/ktr.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/lock_profile.h>
#include <sys/lockmgr.h>
#include <sys/lockstat.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sleepqueue.h>
#ifdef DEBUG_LOCKS
#include <sys/stack.h>
#endif
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <machine/cpu.h>
#ifdef DDB
#include <ddb/ddb.h>
#endif
#ifdef HWPMC_HOOKS
#include <sys/pmckern.h>
PMC_SOFT_DECLARE( , , lock, failed);
#endif
/*
* Hack. There should be prio_t or similar so that this is not necessary.
*/
_Static_assert((PRILASTFLAG * 2) - 1 <= USHRT_MAX,
"prio flags wont fit in u_short pri in struct lock");
CTASSERT(LK_UNLOCKED == (LK_UNLOCKED &
~(LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS)));
#define SQ_EXCLUSIVE_QUEUE 0
#define SQ_SHARED_QUEUE 1
#ifndef INVARIANTS
#define _lockmgr_assert(lk, what, file, line)
#endif
#define TD_SLOCKS_INC(td) ((td)->td_lk_slocks++)
#define TD_SLOCKS_DEC(td) ((td)->td_lk_slocks--)
#ifndef DEBUG_LOCKS
#define STACK_PRINT(lk)
#define STACK_SAVE(lk)
#define STACK_ZERO(lk)
#else
#define STACK_PRINT(lk) stack_print_ddb(&(lk)->lk_stack)
#define STACK_SAVE(lk) stack_save(&(lk)->lk_stack)
#define STACK_ZERO(lk) stack_zero(&(lk)->lk_stack)
#endif
#define LOCK_LOG2(lk, string, arg1, arg2) \
if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \
CTR2(KTR_LOCK, (string), (arg1), (arg2))
#define LOCK_LOG3(lk, string, arg1, arg2, arg3) \
if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \
CTR3(KTR_LOCK, (string), (arg1), (arg2), (arg3))
#define GIANT_DECLARE \
int _i = 0; \
WITNESS_SAVE_DECL(Giant)
#define GIANT_RESTORE() do { \
if (__predict_false(_i > 0)) { \
while (_i--) \
mtx_lock(&Giant); \
WITNESS_RESTORE(&Giant.lock_object, Giant); \
} \
} while (0)
#define GIANT_SAVE() do { \
if (__predict_false(mtx_owned(&Giant))) { \
WITNESS_SAVE(&Giant.lock_object, Giant); \
while (mtx_owned(&Giant)) { \
_i++; \
mtx_unlock(&Giant); \
} \
} \
} while (0)
static bool __always_inline
LK_CAN_SHARE(uintptr_t x, int flags, bool fp)
{
if ((x & (LK_SHARE | LK_EXCLUSIVE_WAITERS | LK_EXCLUSIVE_SPINNERS)) ==
LK_SHARE)
return (true);
if (fp || (!(x & LK_SHARE)))
return (false);
if ((curthread->td_lk_slocks != 0 && !(flags & LK_NODDLKTREAT)) ||
(curthread->td_pflags & TDP_DEADLKTREAT))
return (true);
return (false);
}
#define LK_TRYOP(x) \
((x) & LK_NOWAIT)
#define LK_CAN_WITNESS(x) \
(((x) & LK_NOWITNESS) == 0 && !LK_TRYOP(x))
#define LK_TRYWIT(x) \
(LK_TRYOP(x) ? LOP_TRYLOCK : 0)
#define lockmgr_disowned(lk) \
(((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == LK_KERNPROC)
#define lockmgr_xlocked_v(v) \
(((v) & ~(LK_FLAGMASK & ~LK_SHARE)) == (uintptr_t)curthread)
#define lockmgr_xlocked(lk) lockmgr_xlocked_v(lockmgr_read_value(lk))
static void assert_lockmgr(const struct lock_object *lock, int how);
#ifdef DDB
static void db_show_lockmgr(const struct lock_object *lock);
#endif
static void lock_lockmgr(struct lock_object *lock, uintptr_t how);
#ifdef KDTRACE_HOOKS
static int owner_lockmgr(const struct lock_object *lock,
struct thread **owner);
#endif
static uintptr_t unlock_lockmgr(struct lock_object *lock);
struct lock_class lock_class_lockmgr = {
.lc_name = "lockmgr",
.lc_flags = LC_RECURSABLE | LC_SLEEPABLE | LC_SLEEPLOCK | LC_UPGRADABLE,
.lc_assert = assert_lockmgr,
#ifdef DDB
.lc_ddb_show = db_show_lockmgr,
#endif
.lc_lock = lock_lockmgr,
.lc_unlock = unlock_lockmgr,
#ifdef KDTRACE_HOOKS
.lc_owner = owner_lockmgr,
#endif
};
static __read_mostly bool lk_adaptive = true;
static SYSCTL_NODE(_debug, OID_AUTO, lockmgr, CTLFLAG_RD, NULL, "lockmgr debugging");
SYSCTL_BOOL(_debug_lockmgr, OID_AUTO, adaptive_spinning, CTLFLAG_RW, &lk_adaptive,
0, "");
#define lockmgr_delay locks_delay
struct lockmgr_wait {
const char *iwmesg;
int ipri;
int itimo;
};
static bool __always_inline lockmgr_slock_try(struct lock *lk, uintptr_t *xp,
int flags, bool fp);
static bool __always_inline lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp);
static void
lockmgr_exit(u_int flags, struct lock_object *ilk, int wakeup_swapper)
{
struct lock_class *class;
if (flags & LK_INTERLOCK) {
class = LOCK_CLASS(ilk);
class->lc_unlock(ilk);
}
if (__predict_false(wakeup_swapper))
kick_proc0();
}
static void
lockmgr_note_shared_acquire(struct lock *lk, int contested,
uint64_t waittime, const char *file, int line, int flags)
{
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested,
waittime, file, line, LOCKSTAT_READER);
LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, file, line);
WITNESS_LOCK(&lk->lock_object, LK_TRYWIT(flags), file, line);
TD_LOCKS_INC(curthread);
TD_SLOCKS_INC(curthread);
STACK_SAVE(lk);
}
static void
lockmgr_note_shared_release(struct lock *lk, const char *file, int line)
{
WITNESS_UNLOCK(&lk->lock_object, 0, file, line);
LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, file, line);
TD_LOCKS_DEC(curthread);
TD_SLOCKS_DEC(curthread);
}
static void
lockmgr_note_exclusive_acquire(struct lock *lk, int contested,
uint64_t waittime, const char *file, int line, int flags)
{
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested,
waittime, file, line, LOCKSTAT_WRITER);
LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line);
WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file,
line);
TD_LOCKS_INC(curthread);
STACK_SAVE(lk);
}
static void
lockmgr_note_exclusive_release(struct lock *lk, const char *file, int line)
{
if (LK_HOLDER(lockmgr_read_value(lk)) != LK_KERNPROC) {
WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line);
TD_LOCKS_DEC(curthread);
}
LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0, lk->lk_recurse, file,
line);
}
static __inline struct thread *
lockmgr_xholder(const struct lock *lk)
{
uintptr_t x;
x = lockmgr_read_value(lk);
return ((x & LK_SHARE) ? NULL : (struct thread *)LK_HOLDER(x));
}
/*
* It assumes sleepq_lock held and returns with this one unheld.
* It also assumes the generic interlock is sane and previously checked.
* If LK_INTERLOCK is specified the interlock is not reacquired after the
* sleep.
*/
static __inline int
sleeplk(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *wmesg, int pri, int timo, int queue)
{
GIANT_DECLARE;
struct lock_class *class;
int catch, error;
class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
catch = pri & PCATCH;
pri &= PRIMASK;
error = 0;
LOCK_LOG3(lk, "%s: %p blocking on the %s sleepqueue", __func__, lk,
(queue == SQ_EXCLUSIVE_QUEUE) ? "exclusive" : "shared");
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
if (queue == SQ_EXCLUSIVE_QUEUE && (flags & LK_SLEEPFAIL) != 0) {
if (lk->lk_exslpfail < USHRT_MAX)
lk->lk_exslpfail++;
}
GIANT_SAVE();
sleepq_add(&lk->lock_object, NULL, wmesg, SLEEPQ_LK | (catch ?
SLEEPQ_INTERRUPTIBLE : 0), queue);
if ((flags & LK_TIMELOCK) && timo)
sleepq_set_timeout(&lk->lock_object, timo);
/*
* Decisional switch for real sleeping.
*/
if ((flags & LK_TIMELOCK) && timo && catch)
error = sleepq_timedwait_sig(&lk->lock_object, pri);
else if ((flags & LK_TIMELOCK) && timo)
error = sleepq_timedwait(&lk->lock_object, pri);
else if (catch)
error = sleepq_wait_sig(&lk->lock_object, pri);
else
sleepq_wait(&lk->lock_object, pri);
GIANT_RESTORE();
if ((flags & LK_SLEEPFAIL) && error == 0)
error = ENOLCK;
return (error);
}
static __inline int
wakeupshlk(struct lock *lk, const char *file, int line)
{
uintptr_t v, x, orig_x;
u_int realexslp;
int queue, wakeup_swapper;
wakeup_swapper = 0;
for (;;) {
x = lockmgr_read_value(lk);
if (lockmgr_sunlock_try(lk, &x))
break;
/*
* We should have a sharer with waiters, so enter the hard
* path in order to handle wakeups correctly.
*/
sleepq_lock(&lk->lock_object);
orig_x = lockmgr_read_value(lk);
retry_sleepq:
x = orig_x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
v = LK_UNLOCKED;
/*
* If the lock has exclusive waiters, give them preference in
* order to avoid deadlock with shared runners up.
* If interruptible sleeps left the exclusive queue empty
* avoid a starvation for the threads sleeping on the shared
* queue by giving them precedence and cleaning up the
* exclusive waiters bit anyway.
* Please note that lk_exslpfail count may be lying about
* the real number of waiters with the LK_SLEEPFAIL flag on
* because they may be used in conjunction with interruptible
* sleeps so lk_exslpfail might be considered an 'upper limit'
* bound, including the edge cases.
*/
realexslp = sleepq_sleepcnt(&lk->lock_object,
SQ_EXCLUSIVE_QUEUE);
if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) {
if (lk->lk_exslpfail != USHRT_MAX && lk->lk_exslpfail < realexslp) {
lk->lk_exslpfail = 0;
queue = SQ_EXCLUSIVE_QUEUE;
v |= (x & LK_SHARED_WAITERS);
} else {
lk->lk_exslpfail = 0;
LOCK_LOG2(lk,
"%s: %p has only LK_SLEEPFAIL sleepers",
__func__, lk);
LOCK_LOG2(lk,
"%s: %p waking up threads on the exclusive queue",
__func__, lk);
wakeup_swapper =
sleepq_broadcast(&lk->lock_object,
SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE);
queue = SQ_SHARED_QUEUE;
}
} else {
/*
* Exclusive waiters sleeping with LK_SLEEPFAIL on
* and using interruptible sleeps/timeout may have
* left spourious lk_exslpfail counts on, so clean
* it up anyway.
*/
lk->lk_exslpfail = 0;
queue = SQ_SHARED_QUEUE;
}
if (lockmgr_sunlock_try(lk, &orig_x)) {
sleepq_release(&lk->lock_object);
break;
}
x |= LK_SHARERS_LOCK(1);
if (!atomic_fcmpset_rel_ptr(&lk->lk_lock, &x, v)) {
orig_x = x;
goto retry_sleepq;
}
LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue",
__func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
"exclusive");
wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK,
0, queue);
sleepq_release(&lk->lock_object);
break;
}
LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER);
return (wakeup_swapper);
}
static void
assert_lockmgr(const struct lock_object *lock, int what)
{
panic("lockmgr locks do not support assertions");
}
static void
lock_lockmgr(struct lock_object *lock, uintptr_t how)
{
panic("lockmgr locks do not support sleep interlocking");
}
static uintptr_t
unlock_lockmgr(struct lock_object *lock)
{
panic("lockmgr locks do not support sleep interlocking");
}
#ifdef KDTRACE_HOOKS
static int
owner_lockmgr(const struct lock_object *lock, struct thread **owner)
{
panic("lockmgr locks do not support owner inquiring");
}
#endif
void
lockinit(struct lock *lk, int pri, const char *wmesg, int timo, int flags)
{
int iflags;
MPASS((flags & ~LK_INIT_MASK) == 0);
ASSERT_ATOMIC_LOAD_PTR(lk->lk_lock,
("%s: lockmgr not aligned for %s: %p", __func__, wmesg,
&lk->lk_lock));
iflags = LO_SLEEPABLE | LO_UPGRADABLE;
if (flags & LK_CANRECURSE)
iflags |= LO_RECURSABLE;
if ((flags & LK_NODUP) == 0)
iflags |= LO_DUPOK;
if (flags & LK_NOPROFILE)
iflags |= LO_NOPROFILE;
if ((flags & LK_NOWITNESS) == 0)
iflags |= LO_WITNESS;
if (flags & LK_QUIET)
iflags |= LO_QUIET;
if (flags & LK_IS_VNODE)
iflags |= LO_IS_VNODE;
if (flags & LK_NEW)
iflags |= LO_NEW;
iflags |= flags & LK_NOSHARE;
lock_init(&lk->lock_object, &lock_class_lockmgr, wmesg, NULL, iflags);
lk->lk_lock = LK_UNLOCKED;
lk->lk_recurse = 0;
lk->lk_exslpfail = 0;
lk->lk_timo = timo;
lk->lk_pri = pri;
STACK_ZERO(lk);
}
/*
* XXX: Gross hacks to manipulate external lock flags after
* initialization. Used for certain vnode and buf locks.
*/
void
lockallowshare(struct lock *lk)
{
lockmgr_assert(lk, KA_XLOCKED);
lk->lock_object.lo_flags &= ~LK_NOSHARE;
}
void
lockdisableshare(struct lock *lk)
{
lockmgr_assert(lk, KA_XLOCKED);
lk->lock_object.lo_flags |= LK_NOSHARE;
}
void
lockallowrecurse(struct lock *lk)
{
lockmgr_assert(lk, KA_XLOCKED);
lk->lock_object.lo_flags |= LO_RECURSABLE;
}
void
lockdisablerecurse(struct lock *lk)
{
lockmgr_assert(lk, KA_XLOCKED);
lk->lock_object.lo_flags &= ~LO_RECURSABLE;
}
void
lockdestroy(struct lock *lk)
{
KASSERT(lk->lk_lock == LK_UNLOCKED, ("lockmgr still held"));
KASSERT(lk->lk_recurse == 0, ("lockmgr still recursed"));
KASSERT(lk->lk_exslpfail == 0, ("lockmgr still exclusive waiters"));
lock_destroy(&lk->lock_object);
}
static bool __always_inline
lockmgr_slock_try(struct lock *lk, uintptr_t *xp, int flags, bool fp)
{
/*
* If no other thread has an exclusive lock, or
* no exclusive waiter is present, bump the count of
* sharers. Since we have to preserve the state of
* waiters, if we fail to acquire the shared lock
* loop back and retry.
*/
while (LK_CAN_SHARE(*xp, flags, fp)) {
if (atomic_fcmpset_acq_ptr(&lk->lk_lock, xp,
*xp + LK_ONE_SHARER)) {
return (true);
}
}
return (false);
}
static bool __always_inline
lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp)
{
for (;;) {
if (LK_SHARERS(*xp) > 1 || !(*xp & LK_ALL_WAITERS)) {
if (atomic_fcmpset_rel_ptr(&lk->lk_lock, xp,
*xp - LK_ONE_SHARER))
return (true);
continue;
}
break;
}
return (false);
}
static bool
lockmgr_slock_adaptive(struct lock_delay_arg *lda, struct lock *lk, uintptr_t *xp,
int flags)
{
struct thread *owner;
uintptr_t x;
x = *xp;
MPASS(x != LK_UNLOCKED);
owner = (struct thread *)LK_HOLDER(x);
for (;;) {
MPASS(owner != curthread);
if (owner == (struct thread *)LK_KERNPROC)
return (false);
if ((x & LK_SHARE) && LK_SHARERS(x) > 0)
return (false);
if (owner == NULL)
return (false);
if (!TD_IS_RUNNING(owner))
return (false);
if ((x & LK_ALL_WAITERS) != 0)
return (false);
lock_delay(lda);
x = lockmgr_read_value(lk);
if (LK_CAN_SHARE(x, flags, false)) {
*xp = x;
return (true);
}
owner = (struct thread *)LK_HOLDER(x);
}
}
static __noinline int
lockmgr_slock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *file, int line, struct lockmgr_wait *lwa)
{
uintptr_t tid, x;
int error = 0;
const char *iwmesg;
int ipri, itimo;
#ifdef KDTRACE_HOOKS
uint64_t sleep_time = 0;
#endif
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
int contested = 0;
#endif
struct lock_delay_arg lda;
if (KERNEL_PANICKED())
goto out;
tid = (uintptr_t)curthread;
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
file, line, flags & LK_INTERLOCK ? ilk : NULL);
x = lockmgr_read_value(lk);
lock_delay_arg_init(&lda, &lockmgr_delay);
if (!lk_adaptive)
flags &= ~LK_ADAPTIVE;
/*
* The lock may already be locked exclusive by curthread,
* avoid deadlock.
*/
if (LK_HOLDER(x) == tid) {
LOCK_LOG2(lk,
"%s: %p already held in exclusive mode",
__func__, lk);
error = EDEADLK;
goto out;
}
for (;;) {
if (lockmgr_slock_try(lk, &x, flags, false))
break;
if ((flags & (LK_ADAPTIVE | LK_INTERLOCK)) == LK_ADAPTIVE) {
if (lockmgr_slock_adaptive(&lda, lk, &x, flags))
continue;
}
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&lk->lock_object, false,
&contested, &waittime);
/*
* If the lock is expected to not sleep just give up
* and return.
*/
if (LK_TRYOP(flags)) {
LOCK_LOG2(lk, "%s: %p fails the try operation",
__func__, lk);
error = EBUSY;
break;
}
/*
* Acquire the sleepqueue chain lock because we
* probabilly will need to manipulate waiters flags.
*/
sleepq_lock(&lk->lock_object);
x = lockmgr_read_value(lk);
retry_sleepq:
/*
* if the lock can be acquired in shared mode, try
* again.
*/
if (LK_CAN_SHARE(x, flags, false)) {
sleepq_release(&lk->lock_object);
continue;
}
/*
* Try to set the LK_SHARED_WAITERS flag. If we fail,
* loop back and retry.
*/
if ((x & LK_SHARED_WAITERS) == 0) {
if (!atomic_fcmpset_acq_ptr(&lk->lk_lock, &x,
x | LK_SHARED_WAITERS)) {
goto retry_sleepq;
}
LOCK_LOG2(lk, "%s: %p set shared waiters flag",
__func__, lk);
}
if (lwa == NULL) {
iwmesg = lk->lock_object.lo_name;
ipri = lk->lk_pri;
itimo = lk->lk_timo;
} else {
iwmesg = lwa->iwmesg;
ipri = lwa->ipri;
itimo = lwa->itimo;
}
/*
* As far as we have been unable to acquire the
* shared lock and the shared waiters flag is set,
* we will sleep.
*/
#ifdef KDTRACE_HOOKS
sleep_time -= lockstat_nsecs(&lk->lock_object);
#endif
error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
SQ_SHARED_QUEUE);
#ifdef KDTRACE_HOOKS
sleep_time += lockstat_nsecs(&lk->lock_object);
#endif
flags &= ~LK_INTERLOCK;
if (error) {
LOCK_LOG3(lk,
"%s: interrupted sleep for %p with %d",
__func__, lk, error);
break;
}
LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
__func__, lk);
x = lockmgr_read_value(lk);
}
if (error == 0) {
#ifdef KDTRACE_HOOKS
if (sleep_time != 0)
LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time,
LOCKSTAT_READER, (x & LK_SHARE) == 0,
(x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x));
#endif
#ifdef LOCK_PROFILING
lockmgr_note_shared_acquire(lk, contested, waittime,
file, line, flags);
#else
lockmgr_note_shared_acquire(lk, 0, 0, file, line,
flags);
#endif
}
out:
lockmgr_exit(flags, ilk, 0);
return (error);
}
static bool
lockmgr_xlock_adaptive(struct lock_delay_arg *lda, struct lock *lk, uintptr_t *xp)
{
struct thread *owner;
uintptr_t x;
x = *xp;
MPASS(x != LK_UNLOCKED);
owner = (struct thread *)LK_HOLDER(x);
for (;;) {
MPASS(owner != curthread);
if (owner == NULL)
return (false);
if ((x & LK_SHARE) && LK_SHARERS(x) > 0)
return (false);
if (owner == (struct thread *)LK_KERNPROC)
return (false);
if (!TD_IS_RUNNING(owner))
return (false);
if ((x & LK_ALL_WAITERS) != 0)
return (false);
lock_delay(lda);
x = lockmgr_read_value(lk);
if (x == LK_UNLOCKED) {
*xp = x;
return (true);
}
owner = (struct thread *)LK_HOLDER(x);
}
}
static __noinline int
lockmgr_xlock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *file, int line, struct lockmgr_wait *lwa)
{
struct lock_class *class;
uintptr_t tid, x, v;
int error = 0;
const char *iwmesg;
int ipri, itimo;
#ifdef KDTRACE_HOOKS
uint64_t sleep_time = 0;
#endif
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
int contested = 0;
#endif
struct lock_delay_arg lda;
if (KERNEL_PANICKED())
goto out;
tid = (uintptr_t)curthread;
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
ilk : NULL);
/*
* If curthread already holds the lock and this one is
* allowed to recurse, simply recurse on it.
*/
if (lockmgr_xlocked(lk)) {
if ((flags & LK_CANRECURSE) == 0 &&
(lk->lock_object.lo_flags & LO_RECURSABLE) == 0) {
/*
* If the lock is expected to not panic just
* give up and return.
*/
if (LK_TRYOP(flags)) {
LOCK_LOG2(lk,
"%s: %p fails the try operation",
__func__, lk);
error = EBUSY;
goto out;
}
if (flags & LK_INTERLOCK) {
class = LOCK_CLASS(ilk);
class->lc_unlock(ilk);
}
STACK_PRINT(lk);
panic("%s: recursing on non recursive lockmgr %p "
"@ %s:%d\n", __func__, lk, file, line);
}
atomic_set_ptr(&lk->lk_lock, LK_WRITER_RECURSED);
lk->lk_recurse++;
LOCK_LOG2(lk, "%s: %p recursing", __func__, lk);
LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0,
lk->lk_recurse, file, line);
WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
TD_LOCKS_INC(curthread);
goto out;
}
x = LK_UNLOCKED;
lock_delay_arg_init(&lda, &lockmgr_delay);
if (!lk_adaptive)
flags &= ~LK_ADAPTIVE;
for (;;) {
if (x == LK_UNLOCKED) {
if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x, tid))
break;
continue;
}
if ((flags & (LK_ADAPTIVE | LK_INTERLOCK)) == LK_ADAPTIVE) {
if (lockmgr_xlock_adaptive(&lda, lk, &x))
continue;
}
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&lk->lock_object, false,
&contested, &waittime);
/*
* If the lock is expected to not sleep just give up
* and return.
*/
if (LK_TRYOP(flags)) {
LOCK_LOG2(lk, "%s: %p fails the try operation",
__func__, lk);
error = EBUSY;
break;
}
/*
* Acquire the sleepqueue chain lock because we
* probabilly will need to manipulate waiters flags.
*/
sleepq_lock(&lk->lock_object);
x = lockmgr_read_value(lk);
retry_sleepq:
/*
* if the lock has been released while we spun on
* the sleepqueue chain lock just try again.
*/
if (x == LK_UNLOCKED) {
sleepq_release(&lk->lock_object);
continue;
}
/*
* The lock can be in the state where there is a
* pending queue of waiters, but still no owner.
* This happens when the lock is contested and an
* owner is going to claim the lock.
* If curthread is the one successfully acquiring it
* claim lock ownership and return, preserving waiters
* flags.
*/
v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
if ((x & ~v) == LK_UNLOCKED) {
v &= ~LK_EXCLUSIVE_SPINNERS;
if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x,
tid | v)) {
sleepq_release(&lk->lock_object);
LOCK_LOG2(lk,
"%s: %p claimed by a new writer",
__func__, lk);
break;
}
goto retry_sleepq;
}
/*
* Try to set the LK_EXCLUSIVE_WAITERS flag. If we
* fail, loop back and retry.
*/
if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
if (!atomic_fcmpset_ptr(&lk->lk_lock, &x,
x | LK_EXCLUSIVE_WAITERS)) {
goto retry_sleepq;
}
LOCK_LOG2(lk, "%s: %p set excl waiters flag",
__func__, lk);
}
if (lwa == NULL) {
iwmesg = lk->lock_object.lo_name;
ipri = lk->lk_pri;
itimo = lk->lk_timo;
} else {
iwmesg = lwa->iwmesg;
ipri = lwa->ipri;
itimo = lwa->itimo;
}
/*
* As far as we have been unable to acquire the
* exclusive lock and the exclusive waiters flag
* is set, we will sleep.
*/
#ifdef KDTRACE_HOOKS
sleep_time -= lockstat_nsecs(&lk->lock_object);
#endif
error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
SQ_EXCLUSIVE_QUEUE);
#ifdef KDTRACE_HOOKS
sleep_time += lockstat_nsecs(&lk->lock_object);
#endif
flags &= ~LK_INTERLOCK;
if (error) {
LOCK_LOG3(lk,
"%s: interrupted sleep for %p with %d",
__func__, lk, error);
break;
}
LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
__func__, lk);
x = lockmgr_read_value(lk);
}
if (error == 0) {
#ifdef KDTRACE_HOOKS
if (sleep_time != 0)
LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time,
LOCKSTAT_WRITER, (x & LK_SHARE) == 0,
(x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x));
#endif
#ifdef LOCK_PROFILING
lockmgr_note_exclusive_acquire(lk, contested, waittime,
file, line, flags);
#else
lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
flags);
#endif
}
out:
lockmgr_exit(flags, ilk, 0);
return (error);
}
static __noinline int
lockmgr_upgrade(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *file, int line, struct lockmgr_wait *lwa)
{
uintptr_t tid, v, setv;
int error = 0;
int op;
if (KERNEL_PANICKED())
goto out;
tid = (uintptr_t)curthread;
_lockmgr_assert(lk, KA_SLOCKED, file, line);
op = flags & LK_TYPE_MASK;
v = lockmgr_read_value(lk);
for (;;) {
if (LK_SHARERS(v) > 1) {
if (op == LK_TRYUPGRADE) {
LOCK_LOG2(lk, "%s: %p failed the nowait upgrade",
__func__, lk);
error = EBUSY;
goto out;
}
if (atomic_fcmpset_rel_ptr(&lk->lk_lock, &v,
v - LK_ONE_SHARER)) {
lockmgr_note_shared_release(lk, file, line);
goto out_xlock;
}
continue;
}
MPASS((v & ~LK_ALL_WAITERS) == LK_SHARERS_LOCK(1));
setv = tid;
setv |= (v & LK_ALL_WAITERS);
/*
* Try to switch from one shared lock to an exclusive one.
* We need to preserve waiters flags during the operation.
*/
if (atomic_fcmpset_ptr(&lk->lk_lock, &v, setv)) {
LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file,
line);
WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
LOCKSTAT_RECORD0(lockmgr__upgrade, lk);
TD_SLOCKS_DEC(curthread);
goto out;
}
}
out_xlock:
error = lockmgr_xlock_hard(lk, flags, ilk, file, line, lwa);
flags &= ~LK_INTERLOCK;
out:
lockmgr_exit(flags, ilk, 0);
return (error);
}
int
lockmgr_lock_flags(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *file, int line)
{
struct lock_class *class;
uintptr_t x, tid;
u_int op;
bool locked;
if (KERNEL_PANICKED())
return (0);
op = flags & LK_TYPE_MASK;
locked = false;
switch (op) {
case LK_SHARED:
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
file, line, flags & LK_INTERLOCK ? ilk : NULL);
if (__predict_false(lk->lock_object.lo_flags & LK_NOSHARE))
break;
x = lockmgr_read_value(lk);
if (lockmgr_slock_try(lk, &x, flags, true)) {
lockmgr_note_shared_acquire(lk, 0, 0,
file, line, flags);
locked = true;
} else {
return (lockmgr_slock_hard(lk, flags, ilk, file, line,
NULL));
}
break;
case LK_EXCLUSIVE:
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
ilk : NULL);
tid = (uintptr_t)curthread;
if (lockmgr_read_value(lk) == LK_UNLOCKED &&
atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
flags);
locked = true;
} else {
return (lockmgr_xlock_hard(lk, flags, ilk, file, line,
NULL));
}
break;
case LK_UPGRADE:
case LK_TRYUPGRADE:
return (lockmgr_upgrade(lk, flags, ilk, file, line, NULL));
default:
break;
}
if (__predict_true(locked)) {
if (__predict_false(flags & LK_INTERLOCK)) {
class = LOCK_CLASS(ilk);
class->lc_unlock(ilk);
}
return (0);
} else {
return (__lockmgr_args(lk, flags, ilk, LK_WMESG_DEFAULT,
LK_PRIO_DEFAULT, LK_TIMO_DEFAULT, file, line));
}
}
static __noinline int
lockmgr_sunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk,
const char *file, int line)
{
int wakeup_swapper = 0;
if (KERNEL_PANICKED())
goto out;
wakeup_swapper = wakeupshlk(lk, file, line);
out:
lockmgr_exit(flags, ilk, wakeup_swapper);
return (0);
}
static __noinline int
lockmgr_xunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk,
const char *file, int line)
{
uintptr_t tid, v;
int wakeup_swapper = 0;
u_int realexslp;
int queue;
if (KERNEL_PANICKED())
goto out;
tid = (uintptr_t)curthread;
/*
* As first option, treact the lock as if it has not
* any waiter.
* Fix-up the tid var if the lock has been disowned.
*/
if (LK_HOLDER(x) == LK_KERNPROC)
tid = LK_KERNPROC;
/*
* The lock is held in exclusive mode.
* If the lock is recursed also, then unrecurse it.
*/
if (lockmgr_recursed_v(x)) {
LOCK_LOG2(lk, "%s: %p unrecursing", __func__, lk);
lk->lk_recurse--;
if (lk->lk_recurse == 0)
atomic_clear_ptr(&lk->lk_lock, LK_WRITER_RECURSED);
goto out;
}
if (tid != LK_KERNPROC)
LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk,
LOCKSTAT_WRITER);
if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED))
goto out;
sleepq_lock(&lk->lock_object);
x = lockmgr_read_value(lk);
v = LK_UNLOCKED;
/*
* If the lock has exclusive waiters, give them
* preference in order to avoid deadlock with
* shared runners up.
* If interruptible sleeps left the exclusive queue
* empty avoid a starvation for the threads sleeping
* on the shared queue by giving them precedence
* and cleaning up the exclusive waiters bit anyway.
* Please note that lk_exslpfail count may be lying
* about the real number of waiters with the
* LK_SLEEPFAIL flag on because they may be used in
* conjunction with interruptible sleeps so
* lk_exslpfail might be considered an 'upper limit'
* bound, including the edge cases.
*/
MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
realexslp = sleepq_sleepcnt(&lk->lock_object, SQ_EXCLUSIVE_QUEUE);
if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) {
if (lk->lk_exslpfail != USHRT_MAX && lk->lk_exslpfail < realexslp) {
lk->lk_exslpfail = 0;
queue = SQ_EXCLUSIVE_QUEUE;
v |= (x & LK_SHARED_WAITERS);
} else {
lk->lk_exslpfail = 0;
LOCK_LOG2(lk,
"%s: %p has only LK_SLEEPFAIL sleepers",
__func__, lk);
LOCK_LOG2(lk,
"%s: %p waking up threads on the exclusive queue",
__func__, lk);
wakeup_swapper = sleepq_broadcast(&lk->lock_object,
SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE);
queue = SQ_SHARED_QUEUE;
}
} else {
/*
* Exclusive waiters sleeping with LK_SLEEPFAIL
* on and using interruptible sleeps/timeout
* may have left spourious lk_exslpfail counts
* on, so clean it up anyway.
*/
lk->lk_exslpfail = 0;
queue = SQ_SHARED_QUEUE;
}
LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue",
__func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
"exclusive");
atomic_store_rel_ptr(&lk->lk_lock, v);
wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, queue);
sleepq_release(&lk->lock_object);
out:
lockmgr_exit(flags, ilk, wakeup_swapper);
return (0);
}
/*
* Lightweight entry points for common operations.
*
* Functionality is similar to sx locks, in that none of the additional lockmgr
* features are supported. To be clear, these are NOT supported:
* 1. shared locking disablement
* 2. returning with an error after sleep
* 3. unlocking the interlock
*
* If in doubt, use lockmgr_lock_flags.
*/
int
lockmgr_slock(struct lock *lk, u_int flags, const char *file, int line)
{
uintptr_t x;
MPASS((flags & LK_TYPE_MASK) == LK_SHARED);
MPASS((flags & LK_INTERLOCK) == 0);
MPASS((lk->lock_object.lo_flags & LK_NOSHARE) == 0);
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
file, line, NULL);
x = lockmgr_read_value(lk);
if (__predict_true(lockmgr_slock_try(lk, &x, flags, true))) {
lockmgr_note_shared_acquire(lk, 0, 0, file, line, flags);
return (0);
}
return (lockmgr_slock_hard(lk, flags | LK_ADAPTIVE, NULL, file, line, NULL));
}
int
lockmgr_xlock(struct lock *lk, u_int flags, const char *file, int line)
{
uintptr_t tid;
MPASS((flags & LK_TYPE_MASK) == LK_EXCLUSIVE);
MPASS((flags & LK_INTERLOCK) == 0);
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
LOP_EXCLUSIVE, file, line, NULL);
tid = (uintptr_t)curthread;
if (atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
flags);
return (0);
}
return (lockmgr_xlock_hard(lk, flags | LK_ADAPTIVE, NULL, file, line, NULL));
}
int
lockmgr_unlock(struct lock *lk)
{
uintptr_t x, tid;
const char *file;
int line;
file = __FILE__;
line = __LINE__;
_lockmgr_assert(lk, KA_LOCKED, file, line);
x = lockmgr_read_value(lk);
if (__predict_true(x & LK_SHARE) != 0) {
lockmgr_note_shared_release(lk, file, line);
if (lockmgr_sunlock_try(lk, &x)) {
LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER);
} else {
return (lockmgr_sunlock_hard(lk, x, LK_RELEASE, NULL, file, line));
}
} else {
tid = (uintptr_t)curthread;
lockmgr_note_exclusive_release(lk, file, line);
if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) {
LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk,LOCKSTAT_WRITER);
} else {
return (lockmgr_xunlock_hard(lk, x, LK_RELEASE, NULL, file, line));
}
}
return (0);
}
int
__lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
const char *wmesg, int pri, int timo, const char *file, int line)
{
GIANT_DECLARE;
struct lockmgr_wait lwa;
struct lock_class *class;
const char *iwmesg;
uintptr_t tid, v, x;
u_int op, realexslp;
int error, ipri, itimo, queue, wakeup_swapper;
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
int contested = 0;
#endif
if (KERNEL_PANICKED())
return (0);
error = 0;
tid = (uintptr_t)curthread;
op = (flags & LK_TYPE_MASK);
iwmesg = (wmesg == LK_WMESG_DEFAULT) ? lk->lock_object.lo_name : wmesg;
ipri = (pri == LK_PRIO_DEFAULT) ? lk->lk_pri : pri;
itimo = (timo == LK_TIMO_DEFAULT) ? lk->lk_timo : timo;
lwa.iwmesg = iwmesg;
lwa.ipri = ipri;
lwa.itimo = itimo;
MPASS((flags & ~LK_TOTAL_MASK) == 0);
KASSERT((op & (op - 1)) == 0,
("%s: Invalid requested operation @ %s:%d", __func__, file, line));
KASSERT((flags & (LK_NOWAIT | LK_SLEEPFAIL)) == 0 ||
(op != LK_DOWNGRADE && op != LK_RELEASE),
("%s: Invalid flags in regard of the operation desired @ %s:%d",
__func__, file, line));
KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL,
("%s: LK_INTERLOCK passed without valid interlock @ %s:%d",
__func__, file, line));
KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
("%s: idle thread %p on lockmgr %s @ %s:%d", __func__, curthread,
lk->lock_object.lo_name, file, line));
class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
if (lk->lock_object.lo_flags & LK_NOSHARE) {
switch (op) {
case LK_SHARED:
op = LK_EXCLUSIVE;
break;
case LK_UPGRADE:
case LK_TRYUPGRADE:
case LK_DOWNGRADE:
_lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED,
file, line);
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
return (0);
}
}
wakeup_swapper = 0;
switch (op) {
case LK_SHARED:
return (lockmgr_slock_hard(lk, flags, ilk, file, line, &lwa));
break;
case LK_UPGRADE:
case LK_TRYUPGRADE:
return (lockmgr_upgrade(lk, flags, ilk, file, line, &lwa));
break;
case LK_EXCLUSIVE:
return (lockmgr_xlock_hard(lk, flags, ilk, file, line, &lwa));
break;
case LK_DOWNGRADE:
_lockmgr_assert(lk, KA_XLOCKED, file, line);
WITNESS_DOWNGRADE(&lk->lock_object, 0, file, line);
/*
* Panic if the lock is recursed.
*/
if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) {
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
panic("%s: downgrade a recursed lockmgr %s @ %s:%d\n",
__func__, iwmesg, file, line);
}
TD_SLOCKS_INC(curthread);
/*
* In order to preserve waiters flags, just spin.
*/
for (;;) {
x = lockmgr_read_value(lk);
MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
x &= LK_ALL_WAITERS;
if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
LK_SHARERS_LOCK(1) | x))
break;
cpu_spinwait();
}
LOCK_LOG_LOCK("XDOWNGRADE", &lk->lock_object, 0, 0, file, line);
LOCKSTAT_RECORD0(lockmgr__downgrade, lk);
break;
case LK_RELEASE:
_lockmgr_assert(lk, KA_LOCKED, file, line);
x = lockmgr_read_value(lk);
if (__predict_true(x & LK_SHARE) != 0) {
lockmgr_note_shared_release(lk, file, line);
return (lockmgr_sunlock_hard(lk, x, flags, ilk, file, line));
} else {
lockmgr_note_exclusive_release(lk, file, line);
return (lockmgr_xunlock_hard(lk, x, flags, ilk, file, line));
}
break;
case LK_DRAIN:
if (LK_CAN_WITNESS(flags))
WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
ilk : NULL);
/*
* Trying to drain a lock we already own will result in a
* deadlock.
*/
if (lockmgr_xlocked(lk)) {
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
panic("%s: draining %s with the lock held @ %s:%d\n",
__func__, iwmesg, file, line);
}
for (;;) {
if (lk->lk_lock == LK_UNLOCKED &&
atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid))
break;
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
lock_profile_obtain_lock_failed(&lk->lock_object, false,
&contested, &waittime);
/*
* If the lock is expected to not sleep just give up
* and return.
*/
if (LK_TRYOP(flags)) {
LOCK_LOG2(lk, "%s: %p fails the try operation",
__func__, lk);
error = EBUSY;
break;
}
/*
* Acquire the sleepqueue chain lock because we
* probabilly will need to manipulate waiters flags.
*/
sleepq_lock(&lk->lock_object);
x = lockmgr_read_value(lk);
/*
* if the lock has been released while we spun on
* the sleepqueue chain lock just try again.
*/
if (x == LK_UNLOCKED) {
sleepq_release(&lk->lock_object);
continue;
}
v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
if ((x & ~v) == LK_UNLOCKED) {
v = (x & ~LK_EXCLUSIVE_SPINNERS);
/*
* If interruptible sleeps left the exclusive
* queue empty avoid a starvation for the
* threads sleeping on the shared queue by
* giving them precedence and cleaning up the
* exclusive waiters bit anyway.
* Please note that lk_exslpfail count may be
* lying about the real number of waiters with
* the LK_SLEEPFAIL flag on because they may
* be used in conjunction with interruptible
* sleeps so lk_exslpfail might be considered
* an 'upper limit' bound, including the edge
* cases.
*/
if (v & LK_EXCLUSIVE_WAITERS) {
queue = SQ_EXCLUSIVE_QUEUE;
v &= ~LK_EXCLUSIVE_WAITERS;
} else {
/*
* Exclusive waiters sleeping with
* LK_SLEEPFAIL on and using
* interruptible sleeps/timeout may
* have left spourious lk_exslpfail
* counts on, so clean it up anyway.
*/
MPASS(v & LK_SHARED_WAITERS);
lk->lk_exslpfail = 0;
queue = SQ_SHARED_QUEUE;
v &= ~LK_SHARED_WAITERS;
}
if (queue == SQ_EXCLUSIVE_QUEUE) {
realexslp =
sleepq_sleepcnt(&lk->lock_object,
SQ_EXCLUSIVE_QUEUE);
if (lk->lk_exslpfail >= realexslp) {
lk->lk_exslpfail = 0;
queue = SQ_SHARED_QUEUE;
v &= ~LK_SHARED_WAITERS;
if (realexslp != 0) {
LOCK_LOG2(lk,
"%s: %p has only LK_SLEEPFAIL sleepers",
__func__, lk);
LOCK_LOG2(lk,
"%s: %p waking up threads on the exclusive queue",
__func__, lk);
wakeup_swapper =
sleepq_broadcast(
&lk->lock_object,
SLEEPQ_LK, 0,
SQ_EXCLUSIVE_QUEUE);
}
} else
lk->lk_exslpfail = 0;
}
if (!atomic_cmpset_ptr(&lk->lk_lock, x, v)) {
sleepq_release(&lk->lock_object);
continue;
}
LOCK_LOG3(lk,
"%s: %p waking up all threads on the %s queue",
__func__, lk, queue == SQ_SHARED_QUEUE ?
"shared" : "exclusive");
wakeup_swapper |= sleepq_broadcast(
&lk->lock_object, SLEEPQ_LK, 0, queue);
/*
* If shared waiters have been woken up we need
* to wait for one of them to acquire the lock
* before to set the exclusive waiters in
* order to avoid a deadlock.
*/
if (queue == SQ_SHARED_QUEUE) {
for (v = lk->lk_lock;
(v & LK_SHARE) && !LK_SHARERS(v);
v = lk->lk_lock)
cpu_spinwait();
}
}
/*
* Try to set the LK_EXCLUSIVE_WAITERS flag. If we
* fail, loop back and retry.
*/
if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
if (!atomic_cmpset_ptr(&lk->lk_lock, x,
x | LK_EXCLUSIVE_WAITERS)) {
sleepq_release(&lk->lock_object);
continue;
}
LOCK_LOG2(lk, "%s: %p set drain waiters flag",
__func__, lk);
}
/*
* As far as we have been unable to acquire the
* exclusive lock and the exclusive waiters flag
* is set, we will sleep.
*/
if (flags & LK_INTERLOCK) {
class->lc_unlock(ilk);
flags &= ~LK_INTERLOCK;
}
GIANT_SAVE();
sleepq_add(&lk->lock_object, NULL, iwmesg, SLEEPQ_LK,
SQ_EXCLUSIVE_QUEUE);
sleepq_wait(&lk->lock_object, ipri & PRIMASK);
GIANT_RESTORE();
LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
__func__, lk);
}
if (error == 0) {
lock_profile_obtain_lock_success(&lk->lock_object,
false, contested, waittime, file, line);
LOCK_LOG_LOCK("DRAIN", &lk->lock_object, 0,
lk->lk_recurse, file, line);
WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
LK_TRYWIT(flags), file, line);
TD_LOCKS_INC(curthread);
STACK_SAVE(lk);
}
break;
default:
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
panic("%s: unknown lockmgr request 0x%x\n", __func__, op);
}
if (flags & LK_INTERLOCK)
class->lc_unlock(ilk);
if (wakeup_swapper)
kick_proc0();
return (error);
}
void
_lockmgr_disown(struct lock *lk, const char *file, int line)
{
uintptr_t tid, x;
if (SCHEDULER_STOPPED())
return;
tid = (uintptr_t)curthread;
_lockmgr_assert(lk, KA_XLOCKED, file, line);
/*
* Panic if the lock is recursed.
*/
if (lockmgr_xlocked(lk) && lockmgr_recursed(lk))
panic("%s: disown a recursed lockmgr @ %s:%d\n",
__func__, file, line);
/*
* If the owner is already LK_KERNPROC just skip the whole operation.
*/
if (LK_HOLDER(lk->lk_lock) != tid)
return;
lock_profile_release_lock(&lk->lock_object, false);
LOCKSTAT_RECORD1(lockmgr__disown, lk, LOCKSTAT_WRITER);
LOCK_LOG_LOCK("XDISOWN", &lk->lock_object, 0, 0, file, line);
WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line);
TD_LOCKS_DEC(curthread);
STACK_SAVE(lk);
/*
* In order to preserve waiters flags, just spin.
*/
for (;;) {
x = lockmgr_read_value(lk);
MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
x &= LK_ALL_WAITERS;
if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
LK_KERNPROC | x))
return;
cpu_spinwait();
}
}
void
lockmgr_printinfo(const struct lock *lk)
{
struct thread *td;
uintptr_t x;
if (lk->lk_lock == LK_UNLOCKED)
printf("lock type %s: UNLOCKED\n", lk->lock_object.lo_name);
else if (lk->lk_lock & LK_SHARE)
printf("lock type %s: SHARED (count %ju)\n",
lk->lock_object.lo_name,
(uintmax_t)LK_SHARERS(lk->lk_lock));
else {
td = lockmgr_xholder(lk);
if (td == (struct thread *)LK_KERNPROC)
printf("lock type %s: EXCL by KERNPROC\n",
lk->lock_object.lo_name);
else
printf("lock type %s: EXCL by thread %p "
"(pid %d, %s, tid %d)\n", lk->lock_object.lo_name,
td, td->td_proc->p_pid, td->td_proc->p_comm,
td->td_tid);
}
x = lk->lk_lock;
if (x & LK_EXCLUSIVE_WAITERS)
printf(" with exclusive waiters pending\n");
if (x & LK_SHARED_WAITERS)
printf(" with shared waiters pending\n");
if (x & LK_EXCLUSIVE_SPINNERS)
printf(" with exclusive spinners pending\n");
STACK_PRINT(lk);
}
int
lockstatus(const struct lock *lk)
{
uintptr_t v, x;
int ret;
ret = LK_SHARED;
x = lockmgr_read_value(lk);
v = LK_HOLDER(x);
if ((x & LK_SHARE) == 0) {
if (v == (uintptr_t)curthread || v == LK_KERNPROC)
ret = LK_EXCLUSIVE;
else
ret = LK_EXCLOTHER;
} else if (x == LK_UNLOCKED)
ret = 0;
return (ret);
}
#ifdef INVARIANT_SUPPORT
FEATURE(invariant_support,
"Support for modules compiled with INVARIANTS option");
#ifndef INVARIANTS
#undef _lockmgr_assert
#endif
void
_lockmgr_assert(const struct lock *lk, int what, const char *file, int line)
{
int slocked = 0;
if (KERNEL_PANICKED())
return;
switch (what) {
case KA_SLOCKED:
case KA_SLOCKED | KA_NOTRECURSED:
case KA_SLOCKED | KA_RECURSED:
slocked = 1;
case KA_LOCKED:
case KA_LOCKED | KA_NOTRECURSED:
case KA_LOCKED | KA_RECURSED:
#ifdef WITNESS
/*
* We cannot trust WITNESS if the lock is held in exclusive
* mode and a call to lockmgr_disown() happened.
* Workaround this skipping the check if the lock is held in
* exclusive mode even for the KA_LOCKED case.
*/
if (slocked || (lk->lk_lock & LK_SHARE)) {
witness_assert(&lk->lock_object, what, file, line);
break;
}
#endif
if (lk->lk_lock == LK_UNLOCKED ||
((lk->lk_lock & LK_SHARE) == 0 && (slocked ||
(!lockmgr_xlocked(lk) && !lockmgr_disowned(lk)))))
panic("Lock %s not %slocked @ %s:%d\n",
lk->lock_object.lo_name, slocked ? "share" : "",
file, line);
if ((lk->lk_lock & LK_SHARE) == 0) {
if (lockmgr_recursed(lk)) {
if (what & KA_NOTRECURSED)
panic("Lock %s recursed @ %s:%d\n",
lk->lock_object.lo_name, file,
line);
} else if (what & KA_RECURSED)
panic("Lock %s not recursed @ %s:%d\n",
lk->lock_object.lo_name, file, line);
}
break;
case KA_XLOCKED:
case KA_XLOCKED | KA_NOTRECURSED:
case KA_XLOCKED | KA_RECURSED:
if (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk))
panic("Lock %s not exclusively locked @ %s:%d\n",
lk->lock_object.lo_name, file, line);
if (lockmgr_recursed(lk)) {
if (what & KA_NOTRECURSED)
panic("Lock %s recursed @ %s:%d\n",
lk->lock_object.lo_name, file, line);
} else if (what & KA_RECURSED)
panic("Lock %s not recursed @ %s:%d\n",
lk->lock_object.lo_name, file, line);
break;
case KA_UNLOCKED:
if (lockmgr_xlocked(lk) || lockmgr_disowned(lk))
panic("Lock %s exclusively locked @ %s:%d\n",
lk->lock_object.lo_name, file, line);
break;
default:
panic("Unknown lockmgr assertion: %d @ %s:%d\n", what, file,
line);
}
}
#endif
#ifdef DDB
int
lockmgr_chain(struct thread *td, struct thread **ownerp)
{
const struct lock *lk;
lk = td->td_wchan;
if (LOCK_CLASS(&lk->lock_object) != &lock_class_lockmgr)
return (0);
db_printf("blocked on lockmgr %s", lk->lock_object.lo_name);
if (lk->lk_lock & LK_SHARE)
db_printf("SHARED (count %ju)\n",
(uintmax_t)LK_SHARERS(lk->lk_lock));
else
db_printf("EXCL\n");
*ownerp = lockmgr_xholder(lk);
return (1);
}
static void
db_show_lockmgr(const struct lock_object *lock)
{
struct thread *td;
const struct lock *lk;
lk = (const struct lock *)lock;
db_printf(" state: ");
if (lk->lk_lock == LK_UNLOCKED)
db_printf("UNLOCKED\n");
else if (lk->lk_lock & LK_SHARE)
db_printf("SLOCK: %ju\n", (uintmax_t)LK_SHARERS(lk->lk_lock));
else {
td = lockmgr_xholder(lk);
if (td == (struct thread *)LK_KERNPROC)
db_printf("XLOCK: LK_KERNPROC\n");
else
db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
td->td_tid, td->td_proc->p_pid,
td->td_proc->p_comm);
if (lockmgr_recursed(lk))
db_printf(" recursed: %d\n", lk->lk_recurse);
}
db_printf(" waiters: ");
switch (lk->lk_lock & LK_ALL_WAITERS) {
case LK_SHARED_WAITERS:
db_printf("shared\n");
break;
case LK_EXCLUSIVE_WAITERS:
db_printf("exclusive\n");
break;
case LK_ALL_WAITERS:
db_printf("shared and exclusive\n");
break;
default:
db_printf("none\n");
}
db_printf(" spinners: ");
if (lk->lk_lock & LK_EXCLUSIVE_SPINNERS)
db_printf("exclusive\n");
else
db_printf("none\n");
}
#endif
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