summaryrefslogtreecommitdiffstats
path: root/sys/kern/kern_sx.c
diff options
context:
space:
mode:
Diffstat (limited to 'sys/kern/kern_sx.c')
-rw-r--r--sys/kern/kern_sx.c1213
1 files changed, 1213 insertions, 0 deletions
diff --git a/sys/kern/kern_sx.c b/sys/kern/kern_sx.c
new file mode 100644
index 0000000..af2391f
--- /dev/null
+++ b/sys/kern/kern_sx.c
@@ -0,0 +1,1213 @@
+/*-
+ * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
+ * Copyright (c) 2001 Jason Evans <jasone@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.
+ */
+
+/*
+ * Shared/exclusive locks. This implementation attempts to ensure
+ * deterministic lock granting behavior, so that slocks and xlocks are
+ * interleaved.
+ *
+ * Priority propagation will not generally raise the priority of lock holders,
+ * so should not be relied upon in combination with sx locks.
+ */
+
+#include "opt_ddb.h"
+#include "opt_hwpmc_hooks.h"
+#include "opt_kdtrace.h"
+#include "opt_no_adaptive_sx.h"
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/ktr.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
+#include <sys/proc.h>
+#include <sys/sleepqueue.h>
+#include <sys/sx.h>
+#include <sys/sysctl.h>
+
+#if defined(SMP) && !defined(NO_ADAPTIVE_SX)
+#include <machine/cpu.h>
+#endif
+
+#ifdef DDB
+#include <ddb/ddb.h>
+#endif
+
+#if defined(SMP) && !defined(NO_ADAPTIVE_SX)
+#define ADAPTIVE_SX
+#endif
+
+CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
+
+#ifdef HWPMC_HOOKS
+#include <sys/pmckern.h>
+PMC_SOFT_DECLARE( , , lock, failed);
+#endif
+
+/* Handy macros for sleep queues. */
+#define SQ_EXCLUSIVE_QUEUE 0
+#define SQ_SHARED_QUEUE 1
+
+/*
+ * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
+ * drop Giant anytime we have to sleep or if we adaptively spin.
+ */
+#define GIANT_DECLARE \
+ int _giantcnt = 0; \
+ WITNESS_SAVE_DECL(Giant) \
+
+#define GIANT_SAVE() do { \
+ if (mtx_owned(&Giant)) { \
+ WITNESS_SAVE(&Giant.lock_object, Giant); \
+ while (mtx_owned(&Giant)) { \
+ _giantcnt++; \
+ mtx_unlock(&Giant); \
+ } \
+ } \
+} while (0)
+
+#define GIANT_RESTORE() do { \
+ if (_giantcnt > 0) { \
+ mtx_assert(&Giant, MA_NOTOWNED); \
+ while (_giantcnt--) \
+ mtx_lock(&Giant); \
+ WITNESS_RESTORE(&Giant.lock_object, Giant); \
+ } \
+} while (0)
+
+/*
+ * Returns true if an exclusive lock is recursed. It assumes
+ * curthread currently has an exclusive lock.
+ */
+#define sx_recurse lock_object.lo_data
+#define sx_recursed(sx) ((sx)->sx_recurse != 0)
+
+static void assert_sx(const struct lock_object *lock, int what);
+#ifdef DDB
+static void db_show_sx(const struct lock_object *lock);
+#endif
+static void lock_sx(struct lock_object *lock, int how);
+#ifdef KDTRACE_HOOKS
+static int owner_sx(const struct lock_object *lock, struct thread **owner);
+#endif
+static int unlock_sx(struct lock_object *lock);
+
+struct lock_class lock_class_sx = {
+ .lc_name = "sx",
+ .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
+ .lc_assert = assert_sx,
+#ifdef DDB
+ .lc_ddb_show = db_show_sx,
+#endif
+ .lc_lock = lock_sx,
+ .lc_unlock = unlock_sx,
+#ifdef KDTRACE_HOOKS
+ .lc_owner = owner_sx,
+#endif
+};
+
+#ifndef INVARIANTS
+#define _sx_assert(sx, what, file, line)
+#endif
+
+#ifdef ADAPTIVE_SX
+static u_int asx_retries = 10;
+static u_int asx_loops = 10000;
+static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
+SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
+SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
+#endif
+
+void
+assert_sx(const struct lock_object *lock, int what)
+{
+
+ sx_assert((const struct sx *)lock, what);
+}
+
+void
+lock_sx(struct lock_object *lock, int how)
+{
+ struct sx *sx;
+
+ sx = (struct sx *)lock;
+ if (how)
+ sx_xlock(sx);
+ else
+ sx_slock(sx);
+}
+
+int
+unlock_sx(struct lock_object *lock)
+{
+ struct sx *sx;
+
+ sx = (struct sx *)lock;
+ sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
+ if (sx_xlocked(sx)) {
+ sx_xunlock(sx);
+ return (1);
+ } else {
+ sx_sunlock(sx);
+ return (0);
+ }
+}
+
+#ifdef KDTRACE_HOOKS
+int
+owner_sx(const struct lock_object *lock, struct thread **owner)
+{
+ const struct sx *sx = (const struct sx *)lock;
+ uintptr_t x = sx->sx_lock;
+
+ *owner = (struct thread *)SX_OWNER(x);
+ return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
+ (*owner != NULL));
+}
+#endif
+
+void
+sx_sysinit(void *arg)
+{
+ struct sx_args *sargs = arg;
+
+ sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
+}
+
+void
+sx_init_flags(struct sx *sx, const char *description, int opts)
+{
+ int flags;
+
+ MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
+ SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
+ ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
+ ("%s: sx_lock not aligned for %s: %p", __func__, description,
+ &sx->sx_lock));
+
+ flags = LO_SLEEPABLE | LO_UPGRADABLE;
+ if (opts & SX_DUPOK)
+ flags |= LO_DUPOK;
+ if (opts & SX_NOPROFILE)
+ flags |= LO_NOPROFILE;
+ if (!(opts & SX_NOWITNESS))
+ flags |= LO_WITNESS;
+ if (opts & SX_RECURSE)
+ flags |= LO_RECURSABLE;
+ if (opts & SX_QUIET)
+ flags |= LO_QUIET;
+
+ flags |= opts & SX_NOADAPTIVE;
+ sx->sx_lock = SX_LOCK_UNLOCKED;
+ sx->sx_recurse = 0;
+ lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
+}
+
+void
+sx_destroy(struct sx *sx)
+{
+
+ KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
+ KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
+ sx->sx_lock = SX_LOCK_DESTROYED;
+ lock_destroy(&sx->lock_object);
+}
+
+int
+_sx_slock(struct sx *sx, int opts, const char *file, int line)
+{
+ int error = 0;
+
+ if (SCHEDULER_STOPPED())
+ return (0);
+ KASSERT(!TD_IS_IDLETHREAD(curthread),
+ ("sx_slock() 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_slock() of destroyed sx @ %s:%d", file, line));
+ WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
+ error = __sx_slock(sx, opts, file, line);
+ if (!error) {
+ LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
+ WITNESS_LOCK(&sx->lock_object, 0, file, line);
+ curthread->td_locks++;
+ }
+
+ return (error);
+}
+
+int
+sx_try_slock_(struct sx *sx, const char *file, int line)
+{
+ uintptr_t x;
+
+ if (SCHEDULER_STOPPED())
+ return (1);
+
+ KASSERT(!TD_IS_IDLETHREAD(curthread),
+ ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
+ curthread, sx->lock_object.lo_name, file, line));
+
+ for (;;) {
+ x = sx->sx_lock;
+ KASSERT(x != SX_LOCK_DESTROYED,
+ ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
+ if (!(x & SX_LOCK_SHARED))
+ break;
+ if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
+ LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
+ WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
+ curthread->td_locks++;
+ return (1);
+ }
+ }
+
+ LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
+ return (0);
+}
+
+int
+_sx_xlock(struct sx *sx, int opts, const char *file, int line)
+{
+ int error = 0;
+
+ if (SCHEDULER_STOPPED())
+ return (0);
+ KASSERT(!TD_IS_IDLETHREAD(curthread),
+ ("sx_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_xlock() of destroyed sx @ %s:%d", file, line));
+ WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
+ line, NULL);
+ error = __sx_xlock(sx, curthread, opts, file, line);
+ if (!error) {
+ LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
+ file, line);
+ WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
+ curthread->td_locks++;
+ }
+
+ return (error);
+}
+
+int
+sx_try_xlock_(struct sx *sx, const char *file, int line)
+{
+ int rval;
+
+ if (SCHEDULER_STOPPED())
+ return (1);
+
+ KASSERT(!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);
+ curthread->td_locks++;
+ }
+
+ return (rval);
+}
+
+void
+_sx_sunlock(struct sx *sx, const char *file, int line)
+{
+
+ if (SCHEDULER_STOPPED())
+ return;
+ KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
+ ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
+ _sx_assert(sx, SA_SLOCKED, file, line);
+ curthread->td_locks--;
+ WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
+ LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
+ __sx_sunlock(sx, file, line);
+ LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
+}
+
+void
+_sx_xunlock(struct sx *sx, const char *file, int line)
+{
+
+ if (SCHEDULER_STOPPED())
+ return;
+ 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);
+}
+
+/*
+ * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
+ * This will only succeed if this thread holds a single shared lock.
+ * Return 1 if if the upgrade succeed, 0 otherwise.
+ */
+int
+sx_try_upgrade_(struct sx *sx, const char *file, int line)
+{
+ uintptr_t x;
+ int success;
+
+ if (SCHEDULER_STOPPED())
+ return (1);
+
+ KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
+ ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
+ _sx_assert(sx, SA_SLOCKED, file, line);
+
+ /*
+ * Try to switch from one shared lock to an exclusive lock. We need
+ * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
+ * we will wake up the exclusive waiters when we drop the lock.
+ */
+ x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
+ success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
+ (uintptr_t)curthread | x);
+ LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
+ if (success) {
+ WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
+ file, line);
+ LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
+ }
+ return (success);
+}
+
+/*
+ * 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;
+
+ if (SCHEDULER_STOPPED())
+ return;
+
+ 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_xlock
+ * 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.
+ */
+int
+_sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
+ int line)
+{
+ GIANT_DECLARE;
+#ifdef ADAPTIVE_SX
+ volatile struct thread *owner;
+ u_int i, spintries = 0;
+#endif
+ uintptr_t x;
+#ifdef LOCK_PROFILING
+ uint64_t waittime = 0;
+ int contested = 0;
+#endif
+ int error = 0;
+#ifdef KDTRACE_HOOKS
+ uint64_t spin_cnt = 0;
+ uint64_t sleep_cnt = 0;
+ int64_t sleep_time = 0;
+#endif
+
+ if (SCHEDULER_STOPPED())
+ return (0);
+
+ /* If we already hold an exclusive lock, then recurse. */
+ if (sx_xlocked(sx)) {
+ KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
+ ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
+ sx->lock_object.lo_name, file, line));
+ sx->sx_recurse++;
+ atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
+ return (0);
+ }
+
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
+ sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
+
+ while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
+#ifdef KDTRACE_HOOKS
+ spin_cnt++;
+#endif
+#ifdef HWPMC_HOOKS
+ PMC_SOFT_CALL( , , lock, failed);
+#endif
+ lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
+ &waittime);
+#ifdef ADAPTIVE_SX
+ /*
+ * 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.
+ */
+ x = sx->sx_lock;
+ if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
+ if ((x & SX_LOCK_SHARED) == 0) {
+ x = SX_OWNER(x);
+ owner = (struct thread *)x;
+ if (TD_IS_RUNNING(owner)) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR3(KTR_LOCK,
+ "%s: spinning on %p held by %p",
+ __func__, sx, owner);
+ GIANT_SAVE();
+ while (SX_OWNER(sx->sx_lock) == x &&
+ TD_IS_RUNNING(owner)) {
+ cpu_spinwait();
+#ifdef KDTRACE_HOOKS
+ spin_cnt++;
+#endif
+ }
+ continue;
+ }
+ } else if (SX_SHARERS(x) && spintries < asx_retries) {
+ GIANT_SAVE();
+ spintries++;
+ for (i = 0; i < asx_loops; i++) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR4(KTR_LOCK,
+ "%s: shared spinning on %p with %u and %u",
+ __func__, sx, spintries, i);
+ x = sx->sx_lock;
+ if ((x & SX_LOCK_SHARED) == 0 ||
+ SX_SHARERS(x) == 0)
+ break;
+ cpu_spinwait();
+#ifdef KDTRACE_HOOKS
+ spin_cnt++;
+#endif
+ }
+ if (i != asx_loops)
+ continue;
+ }
+ }
+#endif
+
+ sleepq_lock(&sx->lock_object);
+ x = sx->sx_lock;
+
+ /*
+ * If the lock was released while spinning on the
+ * sleep queue chain lock, try again.
+ */
+ if (x == SX_LOCK_UNLOCKED) {
+ sleepq_release(&sx->lock_object);
+ continue;
+ }
+
+#ifdef ADAPTIVE_SX
+ /*
+ * The current lock owner might have started executing
+ * on another CPU (or the lock could have changed
+ * owners) while we were waiting on the sleep queue
+ * chain lock. If so, drop the sleep queue lock and try
+ * again.
+ */
+ if (!(x & SX_LOCK_SHARED) &&
+ (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
+ owner = (struct thread *)SX_OWNER(x);
+ if (TD_IS_RUNNING(owner)) {
+ sleepq_release(&sx->lock_object);
+ continue;
+ }
+ }
+#endif
+
+ /*
+ * If an exclusive lock was released with both shared
+ * and exclusive waiters and a shared waiter hasn't
+ * woken up and acquired the lock yet, sx_lock will be
+ * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
+ * If we see that value, try to acquire it once. Note
+ * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
+ * as there are other exclusive waiters still. If we
+ * fail, restart the loop.
+ */
+ if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
+ if (atomic_cmpset_acq_ptr(&sx->sx_lock,
+ SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
+ tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
+ sleepq_release(&sx->lock_object);
+ CTR2(KTR_LOCK, "%s: %p claimed by new writer",
+ __func__, sx);
+ break;
+ }
+ sleepq_release(&sx->lock_object);
+ continue;
+ }
+
+ /*
+ * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
+ * than loop back and retry.
+ */
+ if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
+ if (!atomic_cmpset_ptr(&sx->sx_lock, x,
+ x | SX_LOCK_EXCLUSIVE_WAITERS)) {
+ sleepq_release(&sx->lock_object);
+ continue;
+ }
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
+ __func__, sx);
+ }
+
+ /*
+ * Since we have been unable to acquire the exclusive
+ * lock and the exclusive waiters flag is set, we have
+ * to sleep.
+ */
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
+ __func__, sx);
+
+#ifdef KDTRACE_HOOKS
+ sleep_time -= lockstat_nsecs();
+#endif
+ GIANT_SAVE();
+ sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
+ SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
+ SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
+ if (!(opts & SX_INTERRUPTIBLE))
+ sleepq_wait(&sx->lock_object, 0);
+ else
+ error = sleepq_wait_sig(&sx->lock_object, 0);
+#ifdef KDTRACE_HOOKS
+ sleep_time += lockstat_nsecs();
+ sleep_cnt++;
+#endif
+ if (error) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK,
+ "%s: interruptible sleep by %p suspended by signal",
+ __func__, sx);
+ break;
+ }
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
+ __func__, sx);
+ }
+
+ GIANT_RESTORE();
+ if (!error)
+ LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
+ contested, waittime, file, line);
+#ifdef KDTRACE_HOOKS
+ if (sleep_time)
+ LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
+ if (spin_cnt > sleep_cnt)
+ LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
+#endif
+ return (error);
+}
+
+/*
+ * 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();
+}
+
+/*
+ * This function represents the so-called 'hard case' for sx_slock
+ * 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.
+ */
+int
+_sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
+{
+ GIANT_DECLARE;
+#ifdef ADAPTIVE_SX
+ volatile struct thread *owner;
+#endif
+#ifdef LOCK_PROFILING
+ uint64_t waittime = 0;
+ int contested = 0;
+#endif
+ uintptr_t x;
+ int error = 0;
+#ifdef KDTRACE_HOOKS
+ uint64_t spin_cnt = 0;
+ uint64_t sleep_cnt = 0;
+ int64_t sleep_time = 0;
+#endif
+
+ if (SCHEDULER_STOPPED())
+ return (0);
+
+ /*
+ * As with rwlocks, we don't make any attempt to try to block
+ * shared locks once there is an exclusive waiter.
+ */
+ for (;;) {
+#ifdef KDTRACE_HOOKS
+ spin_cnt++;
+#endif
+ x = sx->sx_lock;
+
+ /*
+ * If no other thread has an exclusive lock then try to bump up
+ * the count of sharers. Since we have to preserve the state
+ * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
+ * shared lock loop back and retry.
+ */
+ if (x & SX_LOCK_SHARED) {
+ MPASS(!(x & SX_LOCK_SHARED_WAITERS));
+ if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
+ x + SX_ONE_SHARER)) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR4(KTR_LOCK,
+ "%s: %p succeed %p -> %p", __func__,
+ sx, (void *)x,
+ (void *)(x + SX_ONE_SHARER));
+ break;
+ }
+ continue;
+ }
+#ifdef HWPMC_HOOKS
+ PMC_SOFT_CALL( , , lock, failed);
+#endif
+ lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
+ &waittime);
+
+#ifdef ADAPTIVE_SX
+ /*
+ * If the owner is running on another CPU, spin until
+ * the owner stops running or the state of the lock
+ * changes.
+ */
+ if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
+ x = SX_OWNER(x);
+ owner = (struct thread *)x;
+ if (TD_IS_RUNNING(owner)) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR3(KTR_LOCK,
+ "%s: spinning on %p held by %p",
+ __func__, sx, owner);
+ GIANT_SAVE();
+ while (SX_OWNER(sx->sx_lock) == x &&
+ TD_IS_RUNNING(owner)) {
+#ifdef KDTRACE_HOOKS
+ spin_cnt++;
+#endif
+ cpu_spinwait();
+ }
+ continue;
+ }
+ }
+#endif
+
+ /*
+ * Some other thread already has an exclusive lock, so
+ * start the process of blocking.
+ */
+ sleepq_lock(&sx->lock_object);
+ x = sx->sx_lock;
+
+ /*
+ * The lock could have been released while we spun.
+ * In this case loop back and retry.
+ */
+ if (x & SX_LOCK_SHARED) {
+ sleepq_release(&sx->lock_object);
+ continue;
+ }
+
+#ifdef ADAPTIVE_SX
+ /*
+ * If the owner is running on another CPU, spin until
+ * the owner stops running or the state of the lock
+ * changes.
+ */
+ if (!(x & SX_LOCK_SHARED) &&
+ (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
+ owner = (struct thread *)SX_OWNER(x);
+ if (TD_IS_RUNNING(owner)) {
+ sleepq_release(&sx->lock_object);
+ continue;
+ }
+ }
+#endif
+
+ /*
+ * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
+ * fail to set it drop the sleep queue lock and loop
+ * back.
+ */
+ if (!(x & SX_LOCK_SHARED_WAITERS)) {
+ if (!atomic_cmpset_ptr(&sx->sx_lock, x,
+ x | SX_LOCK_SHARED_WAITERS)) {
+ sleepq_release(&sx->lock_object);
+ continue;
+ }
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
+ __func__, sx);
+ }
+
+ /*
+ * Since we have been unable to acquire the shared lock,
+ * we have to sleep.
+ */
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
+ __func__, sx);
+
+#ifdef KDTRACE_HOOKS
+ sleep_time -= lockstat_nsecs();
+#endif
+ GIANT_SAVE();
+ sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
+ SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
+ SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
+ if (!(opts & SX_INTERRUPTIBLE))
+ sleepq_wait(&sx->lock_object, 0);
+ else
+ error = sleepq_wait_sig(&sx->lock_object, 0);
+#ifdef KDTRACE_HOOKS
+ sleep_time += lockstat_nsecs();
+ sleep_cnt++;
+#endif
+ if (error) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK,
+ "%s: interruptible sleep by %p suspended by signal",
+ __func__, sx);
+ break;
+ }
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
+ __func__, sx);
+ }
+ if (error == 0)
+ LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
+ contested, waittime, file, line);
+#ifdef KDTRACE_HOOKS
+ if (sleep_time)
+ LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
+ if (spin_cnt > sleep_cnt)
+ LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
+#endif
+ GIANT_RESTORE();
+ return (error);
+}
+
+/*
+ * This function represents the so-called 'hard case' for sx_sunlock
+ * 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_sunlock_hard(struct sx *sx, const char *file, int line)
+{
+ uintptr_t x;
+ int wakeup_swapper;
+
+ if (SCHEDULER_STOPPED())
+ return;
+
+ for (;;) {
+ x = sx->sx_lock;
+
+ /*
+ * We should never have sharers while at least one thread
+ * holds a shared lock.
+ */
+ KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
+ ("%s: waiting sharers", __func__));
+
+ /*
+ * See if there is more than one shared lock held. If
+ * so, just drop one and return.
+ */
+ if (SX_SHARERS(x) > 1) {
+ if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
+ x - SX_ONE_SHARER)) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR4(KTR_LOCK,
+ "%s: %p succeeded %p -> %p",
+ __func__, sx, (void *)x,
+ (void *)(x - SX_ONE_SHARER));
+ break;
+ }
+ continue;
+ }
+
+ /*
+ * If there aren't any waiters for an exclusive lock,
+ * then try to drop it quickly.
+ */
+ if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
+ MPASS(x == SX_SHARERS_LOCK(1));
+ if (atomic_cmpset_rel_ptr(&sx->sx_lock,
+ SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p last succeeded",
+ __func__, sx);
+ break;
+ }
+ continue;
+ }
+
+ /*
+ * At this point, there should just be one sharer with
+ * exclusive waiters.
+ */
+ MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
+
+ sleepq_lock(&sx->lock_object);
+
+ /*
+ * Wake up semantic here is quite simple:
+ * Just wake up all the exclusive waiters.
+ * Note that the state of the lock could have changed,
+ * so if it fails loop back and retry.
+ */
+ if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
+ SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
+ SX_LOCK_UNLOCKED)) {
+ sleepq_release(&sx->lock_object);
+ continue;
+ }
+ if (LOCK_LOG_TEST(&sx->lock_object, 0))
+ CTR2(KTR_LOCK, "%s: %p waking up all thread on"
+ "exclusive queue", __func__, sx);
+ wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
+ 0, SQ_EXCLUSIVE_QUEUE);
+ sleepq_release(&sx->lock_object);
+ if (wakeup_swapper)
+ kick_proc0();
+ break;
+ }
+}
+
+#ifdef INVARIANT_SUPPORT
+#ifndef INVARIANTS
+#undef _sx_assert
+#endif
+
+/*
+ * 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);
+ }
+}
+#endif /* INVARIANT_SUPPORT */
+
+#ifdef DDB
+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");
+ }
+}
+
+/*
+ * Check to see if a thread that is blocked on a sleep queue is actually
+ * blocked on an sx lock. If so, output some details and return true.
+ * If the lock has an exclusive owner, return that in *ownerp.
+ */
+int
+sx_chain(struct thread *td, struct thread **ownerp)
+{
+ struct sx *sx;
+
+ /*
+ * Check to see if this thread is blocked on an sx lock.
+ * First, we check the lock class. If that is ok, then we
+ * compare the lock name against the wait message.
+ */
+ sx = td->td_wchan;
+ if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
+ sx->lock_object.lo_name != td->td_wmesg)
+ return (0);
+
+ /* We think we have an sx lock, so output some details. */
+ db_printf("blocked on sx \"%s\" ", td->td_wmesg);
+ *ownerp = sx_xholder(sx);
+ if (sx->sx_lock & SX_LOCK_SHARED)
+ db_printf("SLOCK (count %ju)\n",
+ (uintmax_t)SX_SHARERS(sx->sx_lock));
+ else
+ db_printf("XLOCK\n");
+ return (1);
+}
+#endif
OpenPOWER on IntegriCloud