int
sx_try_xlock_(struct sx *sx, const char *file, int line)
{
int rval;
if (SCHEDULER_STOPPED())
return (1);
KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
curthread, sx->lock_object.lo_name, file, line));
KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
if (sx_xlocked(sx) &&
(sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
sx->sx_recurse++;
atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
rval = 1;
} else
rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
(uintptr_t)curthread);
LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
if (rval) {
WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
file, line);
if (!sx_recursed(sx))
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
sx, 0, 0, file, line, LOCKSTAT_WRITER);
curthread->td_locks++;
}
return (rval);
}
/*
* Downgrade an unrecursed exclusive lock into a single shared lock.
*/
void
_sx_downgrade(struct sx *sx, const char *file, int line)
{
uintptr_t x;
int wakeup_swapper;
KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
("sx_downgrade() of destroyed sx @ %s:%d", file, line));
_sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
#ifndef INVARIANTS
if (sx_recursed(sx))
panic("downgrade of a recursed lock");
#endif
WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
/*
* Try to switch from an exclusive lock with no shared waiters
* to one sharer with no shared waiters. If there are
* exclusive waiters, we don't need to lock the sleep queue so
* long as we preserve the flag. We do one quick try and if
* that fails we grab the sleepq lock to keep the flags from
* changing and do it the slow way.
*
* We have to lock the sleep queue if there are shared waiters
* so we can wake them up.
*/
x = sx->sx_lock;
if (!(x & SX_LOCK_SHARED_WAITERS) &&
atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
(x & SX_LOCK_EXCLUSIVE_WAITERS))) {
LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
return;
}
/*
* Lock the sleep queue so we can read the waiters bits
* without any races and wakeup any shared waiters.
*/
sleepq_lock(&sx->lock_object);
/*
* Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
* shared lock. If there are any shared waiters, wake them up.
*/
wakeup_swapper = 0;
x = sx->sx_lock;
atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
(x & SX_LOCK_EXCLUSIVE_WAITERS));
if (x & SX_LOCK_SHARED_WAITERS)
wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
0, SQ_SHARED_QUEUE);
sleepq_release(&sx->lock_object);
LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
if (wakeup_swapper)
kick_proc0();
}
/*
* This function represents the so-called 'hard case' for sx_xunlock
* operation. All 'easy case' failures are redirected to this. Note
* that ideally this would be a static function, but it needs to be
* accessible from at least sx.h.
*/
void
_sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
{
uintptr_t x;
int queue, wakeup_swapper;
if (SCHEDULER_STOPPED())
return;
MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
/* If the lock is recursed, then unrecurse one level. */
if (sx_xlocked(sx) && sx_recursed(sx)) {
if ((--sx->sx_recurse) == 0)
atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
return;
}
MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
SX_LOCK_EXCLUSIVE_WAITERS));
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
sleepq_lock(&sx->lock_object);
x = SX_LOCK_UNLOCKED;
/*
* The wake up algorithm here is quite simple and probably not
* ideal. It gives precedence to shared waiters if they are
* present. For this condition, we have to preserve the
* state of the exclusive waiters flag.
* If interruptible sleeps left the shared queue empty avoid a
* starvation for the threads sleeping on the exclusive queue by giving
* them precedence and cleaning up the shared waiters bit anyway.
*/
if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
queue = SQ_SHARED_QUEUE;
x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
} else
queue = SQ_EXCLUSIVE_QUEUE;
/* Wake up all the waiters for the specific queue. */
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
__func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
"exclusive");
atomic_store_rel_ptr(&sx->sx_lock, x);
wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
queue);
sleepq_release(&sx->lock_object);
if (wakeup_swapper)
kick_proc0();
}
void
_sx_xunlock(struct sx *sx, const char *file, int line)
{
MPASS(curthread != NULL);
KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
("sx_xunlock() of destroyed sx @ %s:%d", file, line));
_sx_assert(sx, SA_XLOCKED, file, line);
curthread->td_locks--;
WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
line);
if (!sx_recursed(sx))
LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
__sx_xunlock(sx, curthread, file, line);
}
static void
db_show_sx(const struct lock_object *lock)
{
struct thread *td;
const struct sx *sx;
sx = (const struct sx *)lock;
db_printf(" state: ");
if (sx->sx_lock == SX_LOCK_UNLOCKED)
db_printf("UNLOCKED\n");
else if (sx->sx_lock == SX_LOCK_DESTROYED) {
db_printf("DESTROYED\n");
return;
} else if (sx->sx_lock & SX_LOCK_SHARED)
db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
else {
td = sx_xholder(sx);
db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
td->td_tid, td->td_proc->p_pid, td->td_name);
if (sx_recursed(sx))
db_printf(" recursed: %d\n", sx->sx_recurse);
}
db_printf(" waiters: ");
switch(sx->sx_lock &
(SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
case SX_LOCK_SHARED_WAITERS:
db_printf("shared\n");
break;
case SX_LOCK_EXCLUSIVE_WAITERS:
db_printf("exclusive\n");
break;
case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
db_printf("exclusive and shared\n");
break;
default:
db_printf("none\n");
}
}
/*
* In the non-WITNESS case, sx_assert() can only detect that at least
* *some* thread owns an slock, but it cannot guarantee that *this*
* thread owns an slock.
*/
void
_sx_assert(const struct sx *sx, int what, const char *file, int line)
{
#ifndef WITNESS
int slocked = 0;
#endif
if (panicstr != NULL)
return;
switch (what) {
case SA_SLOCKED:
case SA_SLOCKED | SA_NOTRECURSED:
case SA_SLOCKED | SA_RECURSED:
#ifndef WITNESS
slocked = 1;
/* FALLTHROUGH */
#endif
case SA_LOCKED:
case SA_LOCKED | SA_NOTRECURSED:
case SA_LOCKED | SA_RECURSED:
#ifdef WITNESS
witness_assert(&sx->lock_object, what, file, line);
#else
/*
* If some other thread has an exclusive lock or we
* have one and are asserting a shared lock, fail.
* Also, if no one has a lock at all, fail.
*/
if (sx->sx_lock == SX_LOCK_UNLOCKED ||
(!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
sx_xholder(sx) != curthread)))
panic("Lock %s not %slocked @ %s:%d\n",
sx->lock_object.lo_name, slocked ? "share " : "",
file, line);
if (!(sx->sx_lock & SX_LOCK_SHARED)) {
if (sx_recursed(sx)) {
if (what & SA_NOTRECURSED)
panic("Lock %s recursed @ %s:%d\n",
sx->lock_object.lo_name, file,
line);
} else if (what & SA_RECURSED)
panic("Lock %s not recursed @ %s:%d\n",
sx->lock_object.lo_name, file, line);
}
#endif
break;
case SA_XLOCKED:
case SA_XLOCKED | SA_NOTRECURSED:
case SA_XLOCKED | SA_RECURSED:
if (sx_xholder(sx) != curthread)
panic("Lock %s not exclusively locked @ %s:%d\n",
sx->lock_object.lo_name, file, line);
if (sx_recursed(sx)) {
if (what & SA_NOTRECURSED)
panic("Lock %s recursed @ %s:%d\n",
sx->lock_object.lo_name, file, line);
} else if (what & SA_RECURSED)
panic("Lock %s not recursed @ %s:%d\n",
sx->lock_object.lo_name, file, line);
break;
case SA_UNLOCKED:
#ifdef WITNESS
witness_assert(&sx->lock_object, what, file, line);
#else
/*
* If we hold an exclusve lock fail. We can't
* reliably check to see if we hold a shared lock or
* not.
*/
if (sx_xholder(sx) == curthread)
panic("Lock %s exclusively locked @ %s:%d\n",
sx->lock_object.lo_name, file, line);
#endif
break;
default:
panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
line);
}
}
