FreeBSD-5.3/sys/kern/subr_turnstile.c
/*-
* Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Berkeley Software Design Inc's name may not be used to endorse or
* promote products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
* and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
*/
/*
* Implementation of turnstiles used to hold queue of threads blocked on
* non-sleepable locks. Sleepable locks use condition variables to
* implement their queues. Turnstiles differ from a sleep queue in that
* turnstile queue's are assigned to a lock held by an owning thread. Thus,
* when one thread is enqueued onto a turnstile, it can lend its priority
* to the owning thread.
*
* We wish to avoid bloating locks with an embedded turnstile and we do not
* want to use back-pointers in the locks for the same reason. Thus, we
* use a similar approach to that of Solaris 7 as described in Solaris
* Internals by Jim Mauro and Richard McDougall. Turnstiles are looked up
* in a hash table based on the address of the lock. Each entry in the
* hash table is a linked-lists of turnstiles and is called a turnstile
* chain. Each chain contains a spin mutex that protects all of the
* turnstiles in the chain.
*
* Each time a thread is created, a turnstile is malloc'd and attached to
* that thread. When a thread blocks on a lock, if it is the first thread
* to block, it lends its turnstile to the lock. If the lock already has
* a turnstile, then it gives its turnstile to the lock's turnstile's free
* list. When a thread is woken up, it takes a turnstile from the free list
* if there are any other waiters. If it is the only thread blocked on the
* lock, then it reclaims the turnstile associated with the lock and removes
* it from the hash table.
*/
#include "opt_turnstile_profiling.h"
#include <sys/cdefs.h>
__FBSDID("$FreeBSD: src/sys/kern/subr_turnstile.c,v 1.147.2.2 2004/10/08 19:47:23 jhb Exp $");
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sysctl.h>
#include <sys/turnstile.h>
/*
* Constants for the hash table of turnstile chains. TC_SHIFT is a magic
* number chosen because the sleep queue's use the same value for the
* shift. Basically, we ignore the lower 8 bits of the address.
* TC_TABLESIZE must be a power of two for TC_MASK to work properly.
*/
#define TC_TABLESIZE 128 /* Must be power of 2. */
#define TC_MASK (TC_TABLESIZE - 1)
#define TC_SHIFT 8
#define TC_HASH(lock) (((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK)
#define TC_LOOKUP(lock) &turnstile_chains[TC_HASH(lock)]
/*
* There are three different lists of turnstiles as follows. The list
* connected by ts_link entries is a per-thread list of all the turnstiles
* attached to locks that we own. This is used to fixup our priority when
* a lock is released. The other two lists use the ts_hash entries. The
* first of these two is the turnstile chain list that a turnstile is on
* when it is attached to a lock. The second list to use ts_hash is the
* free list hung off of a turnstile that is attached to a lock.
*
* Each turnstile contains two lists of threads. The ts_blocked list is
* a linked list of threads blocked on the turnstile's lock. The
* ts_pending list is a linked list of threads previously awakened by
* turnstile_signal() or turnstile_wait() that are waiting to be put on
* the run queue.
*
* Locking key:
* c - turnstile chain lock
* q - td_contested lock
*/
struct turnstile {
TAILQ_HEAD(, thread) ts_blocked; /* (c + q) Blocked threads. */
TAILQ_HEAD(, thread) ts_pending; /* (c) Pending threads. */
LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */
LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */
LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */
struct lock_object *ts_lockobj; /* (c) Lock we reference. */
struct thread *ts_owner; /* (c + q) Who owns the lock. */
};
struct turnstile_chain {
LIST_HEAD(, turnstile) tc_turnstiles; /* List of turnstiles. */
struct mtx tc_lock; /* Spin lock for this chain. */
#ifdef TURNSTILE_PROFILING
u_int tc_depth; /* Length of tc_queues. */
u_int tc_max_depth; /* Max length of tc_queues. */
#endif
};
#ifdef TURNSTILE_PROFILING
u_int turnstile_max_depth;
SYSCTL_NODE(_debug, OID_AUTO, turnstile, CTLFLAG_RD, 0, "turnstile profiling");
SYSCTL_NODE(_debug_turnstile, OID_AUTO, chains, CTLFLAG_RD, 0,
"turnstile chain stats");
SYSCTL_UINT(_debug_turnstile, OID_AUTO, max_depth, CTLFLAG_RD,
&turnstile_max_depth, 0, "maxmimum depth achieved of a single chain");
#endif
static struct mtx td_contested_lock;
static struct turnstile_chain turnstile_chains[TC_TABLESIZE];
MALLOC_DEFINE(M_TURNSTILE, "turnstiles", "turnstiles");
/*
* Prototypes for non-exported routines.
*/
static void init_turnstile0(void *dummy);
#ifdef TURNSTILE_PROFILING
static void init_turnstile_profiling(void *arg);
#endif
static void propagate_priority(struct thread *);
static void turnstile_setowner(struct turnstile *ts, struct thread *owner);
/*
* Walks the chain of turnstiles and their owners to propagate the priority
* of the thread being blocked to all the threads holding locks that have to
* release their locks before this thread can run again.
*/
static void
propagate_priority(struct thread *td)
{
struct turnstile_chain *tc;
struct turnstile *ts;
struct thread *td1;
int pri;
mtx_assert(&sched_lock, MA_OWNED);
pri = td->td_priority;
ts = td->td_blocked;
for (;;) {
td = ts->ts_owner;
if (td == NULL) {
/*
* This really isn't quite right. Really
* ought to bump priority of thread that
* next acquires the lock.
*/
return;
}
MPASS(td->td_proc != NULL);
MPASS(td->td_proc->p_magic == P_MAGIC);
/*
* XXX: The owner of a turnstile can be stale if it is the
* first thread to grab a slock of a sx lock. In that case
* it is possible for us to be at SSLEEP or some other
* weird state. We should probably just return if the state
* isn't SRUN or SLOCK.
*/
KASSERT(!TD_IS_SLEEPING(td),
("sleeping thread (pid %d) owns a non-sleepable lock",
td->td_proc->p_pid));
/*
* If this thread already has higher priority than the
* thread that is being blocked, we are finished.
*/
if (td->td_priority <= pri)
return;
/*
* If lock holder is actually running, just bump priority.
*/
if (TD_IS_RUNNING(td)) {
td->td_priority = pri;
return;
}
#ifndef SMP
/*
* For UP, we check to see if td is curthread (this shouldn't
* ever happen however as it would mean we are in a deadlock.)
*/
KASSERT(td != curthread, ("Deadlock detected"));
#endif
/*
* If on run queue move to new run queue, and quit.
* XXXKSE this gets a lot more complicated under threads
* but try anyhow.
*/
if (TD_ON_RUNQ(td)) {
MPASS(td->td_blocked == NULL);
sched_prio(td, pri);
return;
}
/*
* Bump this thread's priority.
*/
td->td_priority = pri;
/*
* If we aren't blocked on a lock, we should be.
*/
KASSERT(TD_ON_LOCK(td), (
"process %d(%s):%d holds %s but isn't blocked on a lock\n",
td->td_proc->p_pid, td->td_proc->p_comm, td->td_state,
ts->ts_lockobj->lo_name));
/*
* Pick up the lock that td is blocked on.
*/
ts = td->td_blocked;
MPASS(ts != NULL);
tc = TC_LOOKUP(ts->ts_lockobj);
mtx_lock_spin(&tc->tc_lock);
/*
* This thread may not be blocked on this turnstile anymore
* but instead might already be woken up on another CPU
* that is waiting on sched_lock in turnstile_unpend() to
* finish waking this thread up. We can detect this case
* by checking to see if this thread has been given a
* turnstile by either turnstile_signal() or
* turnstile_broadcast(). In this case, treat the thread as
* if it was already running.
*/
if (td->td_turnstile != NULL) {
mtx_unlock_spin(&tc->tc_lock);
return;
}
/*
* Check if the thread needs to be moved up on
* the blocked chain. It doesn't need to be moved
* if it is already at the head of the list or if
* the item in front of it still has a higher priority.
*/
if (td == TAILQ_FIRST(&ts->ts_blocked)) {
mtx_unlock_spin(&tc->tc_lock);
continue;
}
td1 = TAILQ_PREV(td, threadqueue, td_lockq);
if (td1->td_priority <= pri) {
mtx_unlock_spin(&tc->tc_lock);
continue;
}
/*
* Remove thread from blocked chain and determine where
* it should be moved up to. Since we know that td1 has
* a lower priority than td, we know that at least one
* thread in the chain has a lower priority and that
* td1 will thus not be NULL after the loop.
*/
mtx_lock_spin(&td_contested_lock);
TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq);
TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq) {
MPASS(td1->td_proc->p_magic == P_MAGIC);
if (td1->td_priority > pri)
break;
}
MPASS(td1 != NULL);
TAILQ_INSERT_BEFORE(td1, td, td_lockq);
mtx_unlock_spin(&td_contested_lock);
CTR4(KTR_LOCK,
"propagate_priority: td %p moved before %p on [%p] %s",
td, td1, ts->ts_lockobj, ts->ts_lockobj->lo_name);
mtx_unlock_spin(&tc->tc_lock);
}
}
/*
* Early initialization of turnstiles. This is not done via a SYSINIT()
* since this needs to be initialized very early when mutexes are first
* initialized.
*/
void
init_turnstiles(void)
{
int i;
for (i = 0; i < TC_TABLESIZE; i++) {
LIST_INIT(&turnstile_chains[i].tc_turnstiles);
mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain",
NULL, MTX_SPIN);
}
mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN);
thread0.td_turnstile = NULL;
}
#ifdef TURNSTILE_PROFILING
static void
init_turnstile_profiling(void *arg)
{
struct sysctl_oid *chain_oid;
char chain_name[10];
int i;
for (i = 0; i < TC_TABLESIZE; i++) {
snprintf(chain_name, sizeof(chain_name), "%d", i);
chain_oid = SYSCTL_ADD_NODE(NULL,
SYSCTL_STATIC_CHILDREN(_debug_turnstile_chains), OID_AUTO,
chain_name, CTLFLAG_RD, NULL, "turnstile chain stats");
SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
"depth", CTLFLAG_RD, &turnstile_chains[i].tc_depth, 0,
NULL);
SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
"max_depth", CTLFLAG_RD, &turnstile_chains[i].tc_max_depth,
0, NULL);
}
}
SYSINIT(turnstile_profiling, SI_SUB_LOCK, SI_ORDER_ANY,
init_turnstile_profiling, NULL);
#endif
static void
init_turnstile0(void *dummy)
{
thread0.td_turnstile = turnstile_alloc();
}
SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL);
/*
* Set the owner of the lock this turnstile is attached to.
*/
static void
turnstile_setowner(struct turnstile *ts, struct thread *owner)
{
mtx_assert(&td_contested_lock, MA_OWNED);
MPASS(owner->td_proc->p_magic == P_MAGIC);
MPASS(ts->ts_owner == NULL);
ts->ts_owner = owner;
LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link);
}
/*
* Malloc a turnstile for a new thread, initialize it and return it.
*/
struct turnstile *
turnstile_alloc(void)
{
struct turnstile *ts;
ts = malloc(sizeof(struct turnstile), M_TURNSTILE, M_WAITOK | M_ZERO);
TAILQ_INIT(&ts->ts_blocked);
TAILQ_INIT(&ts->ts_pending);
LIST_INIT(&ts->ts_free);
return (ts);
}
/*
* Free a turnstile when a thread is destroyed.
*/
void
turnstile_free(struct turnstile *ts)
{
MPASS(ts != NULL);
MPASS(TAILQ_EMPTY(&ts->ts_blocked));
MPASS(TAILQ_EMPTY(&ts->ts_pending));
free(ts, M_TURNSTILE);
}
/*
* Look up the turnstile for a lock in the hash table locking the associated
* turnstile chain along the way. Return with the turnstile chain locked.
* If no turnstile is found in the hash table, NULL is returned.
*/
struct turnstile *
turnstile_lookup(struct lock_object *lock)
{
struct turnstile_chain *tc;
struct turnstile *ts;
tc = TC_LOOKUP(lock);
mtx_lock_spin(&tc->tc_lock);
LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
if (ts->ts_lockobj == lock)
return (ts);
return (NULL);
}
/*
* Unlock the turnstile chain associated with a given lock.
*/
void
turnstile_release(struct lock_object *lock)
{
struct turnstile_chain *tc;
tc = TC_LOOKUP(lock);
mtx_unlock_spin(&tc->tc_lock);
}
/*
* Take ownership of a turnstile and adjust the priority of the new
* owner appropriately.
*/
void
turnstile_claim(struct turnstile *ts)
{
struct turnstile_chain *tc;
struct thread *td, *owner;
tc = TC_LOOKUP(ts->ts_lockobj);
mtx_assert(&tc->tc_lock, MA_OWNED);
owner = curthread;
mtx_lock_spin(&td_contested_lock);
turnstile_setowner(ts, owner);
mtx_unlock_spin(&td_contested_lock);
td = TAILQ_FIRST(&ts->ts_blocked);
MPASS(td != NULL);
MPASS(td->td_proc->p_magic == P_MAGIC);
mtx_unlock_spin(&tc->tc_lock);
/*
* Update the priority of the new owner if needed.
*/
mtx_lock_spin(&sched_lock);
if (td->td_priority < owner->td_priority)
owner->td_priority = td->td_priority;
mtx_unlock_spin(&sched_lock);
}
/*
* Block the current thread on the turnstile ts. This function will context
* switch and not return until this thread has been woken back up. This
* function must be called with the appropriate turnstile chain locked and
* will return with it unlocked.
*/
void
turnstile_wait(struct turnstile *ts, struct lock_object *lock,
struct thread *owner)
{
struct turnstile_chain *tc;
struct thread *td, *td1;
td = curthread;
tc = TC_LOOKUP(lock);
mtx_assert(&tc->tc_lock, MA_OWNED);
MPASS(td->td_turnstile != NULL);
MPASS(owner != NULL);
MPASS(owner->td_proc->p_magic == P_MAGIC);
/* If the passed in turnstile is NULL, use this thread's turnstile. */
if (ts == NULL) {
#ifdef TURNSTILE_PROFILING
tc->tc_depth++;
if (tc->tc_depth > tc->tc_max_depth) {
tc->tc_max_depth = tc->tc_depth;
if (tc->tc_max_depth > turnstile_max_depth)
turnstile_max_depth = tc->tc_max_depth;
}
#endif
ts = td->td_turnstile;
LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash);
KASSERT(TAILQ_EMPTY(&ts->ts_pending),
("thread's turnstile has pending threads"));
KASSERT(TAILQ_EMPTY(&ts->ts_blocked),
("thread's turnstile has a non-empty queue"));
KASSERT(LIST_EMPTY(&ts->ts_free),
("thread's turnstile has a non-empty free list"));
KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer"));
ts->ts_lockobj = lock;
mtx_lock_spin(&td_contested_lock);
TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
turnstile_setowner(ts, owner);
mtx_unlock_spin(&td_contested_lock);
} else {
TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq)
if (td1->td_priority > td->td_priority)
break;
mtx_lock_spin(&td_contested_lock);
if (td1 != NULL)
TAILQ_INSERT_BEFORE(td1, td, td_lockq);
else
TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
mtx_unlock_spin(&td_contested_lock);
MPASS(td->td_turnstile != NULL);
LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash);
MPASS(owner == ts->ts_owner);
}
td->td_turnstile = NULL;
mtx_unlock_spin(&tc->tc_lock);
mtx_lock_spin(&sched_lock);
/*
* Handle race condition where a thread on another CPU that owns
* lock 'lock' could have woken us in between us dropping the
* turnstile chain lock and acquiring the sched_lock.
*/
if (td->td_flags & TDF_TSNOBLOCK) {
td->td_flags &= ~TDF_TSNOBLOCK;
mtx_unlock_spin(&sched_lock);
return;
}
#ifdef notyet
/*
* If we're borrowing an interrupted thread's VM context, we
* must clean up before going to sleep.
*/
if (td->td_ithd != NULL) {
struct ithd *it = td->td_ithd;
if (it->it_interrupted) {
if (LOCK_LOG_TEST(lock, 0))
CTR3(KTR_LOCK, "%s: %p interrupted %p",
__func__, it, it->it_interrupted);
intr_thd_fixup(it);
}
}
#endif
/* Save who we are blocked on and switch. */
td->td_blocked = ts;
td->td_lockname = lock->lo_name;
TD_SET_LOCK(td);
propagate_priority(td);
if (LOCK_LOG_TEST(lock, 0))
CTR4(KTR_LOCK, "%s: td %p blocked on [%p] %s", __func__, td,
lock, lock->lo_name);
mi_switch(SW_VOL, NULL);
if (LOCK_LOG_TEST(lock, 0))
CTR4(KTR_LOCK, "%s: td %p free from blocked on [%p] %s",
__func__, td, lock, lock->lo_name);
mtx_unlock_spin(&sched_lock);
}
/*
* Pick the highest priority thread on this turnstile and put it on the
* pending list. This must be called with the turnstile chain locked.
*/
int
turnstile_signal(struct turnstile *ts)
{
struct turnstile_chain *tc;
struct thread *td;
int empty;
MPASS(ts != NULL);
MPASS(curthread->td_proc->p_magic == P_MAGIC);
MPASS(ts->ts_owner == curthread);
tc = TC_LOOKUP(ts->ts_lockobj);
mtx_assert(&tc->tc_lock, MA_OWNED);
/*
* Pick the highest priority thread blocked on this lock and
* move it to the pending list.
*/
td = TAILQ_FIRST(&ts->ts_blocked);
MPASS(td->td_proc->p_magic == P_MAGIC);
mtx_lock_spin(&td_contested_lock);
TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq);
mtx_unlock_spin(&td_contested_lock);
TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq);
/*
* If the turnstile is now empty, remove it from its chain and
* give it to the about-to-be-woken thread. Otherwise take a
* turnstile from the free list and give it to the thread.
*/
empty = TAILQ_EMPTY(&ts->ts_blocked);
if (empty) {
MPASS(LIST_EMPTY(&ts->ts_free));
#ifdef TURNSTILE_PROFILING
tc->tc_depth--;
#endif
} else
ts = LIST_FIRST(&ts->ts_free);
MPASS(ts != NULL);
LIST_REMOVE(ts, ts_hash);
td->td_turnstile = ts;
return (empty);
}
/*
* Put all blocked threads on the pending list. This must be called with
* the turnstile chain locked.
*/
void
turnstile_broadcast(struct turnstile *ts)
{
struct turnstile_chain *tc;
struct turnstile *ts1;
struct thread *td;
MPASS(ts != NULL);
MPASS(curthread->td_proc->p_magic == P_MAGIC);
MPASS(ts->ts_owner == curthread);
tc = TC_LOOKUP(ts->ts_lockobj);
mtx_assert(&tc->tc_lock, MA_OWNED);
/*
* Transfer the blocked list to the pending list.
*/
mtx_lock_spin(&td_contested_lock);
TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked, td_lockq);
mtx_unlock_spin(&td_contested_lock);
/*
* Give a turnstile to each thread. The last thread gets
* this turnstile.
*/
TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) {
if (LIST_EMPTY(&ts->ts_free)) {
MPASS(TAILQ_NEXT(td, td_lockq) == NULL);
ts1 = ts;
#ifdef TURNSTILE_PROFILING
tc->tc_depth--;
#endif
} else
ts1 = LIST_FIRST(&ts->ts_free);
MPASS(ts1 != NULL);
LIST_REMOVE(ts1, ts_hash);
td->td_turnstile = ts1;
}
}
/*
* Wakeup all threads on the pending list and adjust the priority of the
* current thread appropriately. This must be called with the turnstile
* chain locked.
*/
void
turnstile_unpend(struct turnstile *ts)
{
TAILQ_HEAD( ,thread) pending_threads;
struct turnstile_chain *tc;
struct thread *td;
int cp, pri;
MPASS(ts != NULL);
MPASS(ts->ts_owner == curthread);
tc = TC_LOOKUP(ts->ts_lockobj);
mtx_assert(&tc->tc_lock, MA_OWNED);
MPASS(!TAILQ_EMPTY(&ts->ts_pending));
/*
* Move the list of pending threads out of the turnstile and
* into a local variable.
*/
TAILQ_INIT(&pending_threads);
TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq);
#ifdef INVARIANTS
if (TAILQ_EMPTY(&ts->ts_blocked))
ts->ts_lockobj = NULL;
#endif
/*
* Remove the turnstile from this thread's list of contested locks
* since this thread doesn't own it anymore. New threads will
* not be blocking on the turnstile until it is claimed by a new
* owner.
*/
mtx_lock_spin(&td_contested_lock);
ts->ts_owner = NULL;
LIST_REMOVE(ts, ts_link);
mtx_unlock_spin(&td_contested_lock);
critical_enter();
mtx_unlock_spin(&tc->tc_lock);
/*
* Adjust the priority of curthread based on other contested
* locks it owns. Don't lower the priority below the base
* priority however.
*/
td = curthread;
pri = PRI_MAX;
mtx_lock_spin(&sched_lock);
mtx_lock_spin(&td_contested_lock);
LIST_FOREACH(ts, &td->td_contested, ts_link) {
cp = TAILQ_FIRST(&ts->ts_blocked)->td_priority;
if (cp < pri)
pri = cp;
}
mtx_unlock_spin(&td_contested_lock);
if (pri > td->td_base_pri)
pri = td->td_base_pri;
td->td_priority = pri;
/*
* Wake up all the pending threads. If a thread is not blocked
* on a lock, then it is currently executing on another CPU in
* turnstile_wait() or sitting on a run queue waiting to resume
* in turnstile_wait(). Set a flag to force it to try to acquire
* the lock again instead of blocking.
*/
while (!TAILQ_EMPTY(&pending_threads)) {
td = TAILQ_FIRST(&pending_threads);
TAILQ_REMOVE(&pending_threads, td, td_lockq);
MPASS(td->td_proc->p_magic == P_MAGIC);
if (TD_ON_LOCK(td)) {
td->td_blocked = NULL;
td->td_lockname = NULL;
TD_CLR_LOCK(td);
MPASS(TD_CAN_RUN(td));
setrunqueue(td, SRQ_BORING);
} else {
td->td_flags |= TDF_TSNOBLOCK;
MPASS(TD_IS_RUNNING(td) || TD_ON_RUNQ(td));
}
}
critical_exit();
mtx_unlock_spin(&sched_lock);
}
/*
* Return the first thread in a turnstile.
*/
struct thread *
turnstile_head(struct turnstile *ts)
{
#ifdef INVARIANTS
struct turnstile_chain *tc;
MPASS(ts != NULL);
tc = TC_LOOKUP(ts->ts_lockobj);
mtx_assert(&tc->tc_lock, MA_OWNED);
#endif
return (TAILQ_FIRST(&ts->ts_blocked));
}
/*
* Returns true if a turnstile is empty.
*/
int
turnstile_empty(struct turnstile *ts)
{
#ifdef INVARIANTS
struct turnstile_chain *tc;
MPASS(ts != NULL);
tc = TC_LOOKUP(ts->ts_lockobj);
mtx_assert(&tc->tc_lock, MA_OWNED);
#endif
return (TAILQ_EMPTY(&ts->ts_blocked));
}