Index: head/sys/kern/kern_mutex.c =================================================================== --- head/sys/kern/kern_mutex.c (revision 193034) +++ head/sys/kern/kern_mutex.c (revision 193035) @@ -1,911 +1,914 @@ /*- * 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 $ */ /* * Machine independent bits of mutex implementation. */ #include __FBSDID("$FreeBSD$"); #include "opt_adaptive_mutexes.h" #include "opt_ddb.h" #include "opt_global.h" #include "opt_kdtrace.h" #include "opt_sched.h" #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #if defined(SMP) && !defined(NO_ADAPTIVE_MUTEXES) #define ADAPTIVE_MUTEXES #endif /* * Internal utility macros. */ #define mtx_unowned(m) ((m)->mtx_lock == MTX_UNOWNED) #define mtx_destroyed(m) ((m)->mtx_lock == MTX_DESTROYED) #define mtx_owner(m) ((struct thread *)((m)->mtx_lock & ~MTX_FLAGMASK)) static void assert_mtx(struct lock_object *lock, int what); #ifdef DDB static void db_show_mtx(struct lock_object *lock); #endif static void lock_mtx(struct lock_object *lock, int how); static void lock_spin(struct lock_object *lock, int how); #ifdef KDTRACE_HOOKS static int owner_mtx(struct lock_object *lock, struct thread **owner); #endif static int unlock_mtx(struct lock_object *lock); static int unlock_spin(struct lock_object *lock); /* * Lock classes for sleep and spin mutexes. */ struct lock_class lock_class_mtx_sleep = { .lc_name = "sleep mutex", .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE, .lc_assert = assert_mtx, #ifdef DDB .lc_ddb_show = db_show_mtx, #endif .lc_lock = lock_mtx, .lc_unlock = unlock_mtx, #ifdef KDTRACE_HOOKS .lc_owner = owner_mtx, #endif }; struct lock_class lock_class_mtx_spin = { .lc_name = "spin mutex", .lc_flags = LC_SPINLOCK | LC_RECURSABLE, .lc_assert = assert_mtx, #ifdef DDB .lc_ddb_show = db_show_mtx, #endif .lc_lock = lock_spin, .lc_unlock = unlock_spin, #ifdef KDTRACE_HOOKS .lc_owner = owner_mtx, #endif }; /* * System-wide mutexes */ struct mtx blocked_lock; struct mtx Giant; void assert_mtx(struct lock_object *lock, int what) { mtx_assert((struct mtx *)lock, what); } void lock_mtx(struct lock_object *lock, int how) { mtx_lock((struct mtx *)lock); } void lock_spin(struct lock_object *lock, int how) { panic("spin locks can only use msleep_spin"); } int unlock_mtx(struct lock_object *lock) { struct mtx *m; m = (struct mtx *)lock; mtx_assert(m, MA_OWNED | MA_NOTRECURSED); mtx_unlock(m); return (0); } int unlock_spin(struct lock_object *lock) { panic("spin locks can only use msleep_spin"); } #ifdef KDTRACE_HOOKS int owner_mtx(struct lock_object *lock, struct thread **owner) { struct mtx *m = (struct mtx *)lock; *owner = mtx_owner(m); return (mtx_unowned(m) == 0); } #endif /* * Function versions of the inlined __mtx_* macros. These are used by * modules and can also be called from assembly language if needed. */ void _mtx_lock_flags(struct mtx *m, int opts, const char *file, int line) { MPASS(curthread != NULL); KASSERT(m->mtx_lock != MTX_DESTROYED, ("mtx_lock() of destroyed mutex @ %s:%d", file, line)); KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep, ("mtx_lock() of spin mutex %s @ %s:%d", m->lock_object.lo_name, file, line)); WITNESS_CHECKORDER(&m->lock_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL); _get_sleep_lock(m, curthread, opts, file, line); LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file, line); WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line); curthread->td_locks++; } void _mtx_unlock_flags(struct mtx *m, int opts, const char *file, int line) { MPASS(curthread != NULL); KASSERT(m->mtx_lock != MTX_DESTROYED, ("mtx_unlock() of destroyed mutex @ %s:%d", file, line)); KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep, ("mtx_unlock() of spin mutex %s @ %s:%d", m->lock_object.lo_name, file, line)); curthread->td_locks--; WITNESS_UNLOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line); LOCK_LOG_LOCK("UNLOCK", &m->lock_object, opts, m->mtx_recurse, file, line); mtx_assert(m, MA_OWNED); if (m->mtx_recurse == 0) LOCKSTAT_PROFILE_RELEASE_LOCK(LS_MTX_UNLOCK_RELEASE, m); _rel_sleep_lock(m, curthread, opts, file, line); } void _mtx_lock_spin_flags(struct mtx *m, int opts, const char *file, int line) { MPASS(curthread != NULL); KASSERT(m->mtx_lock != MTX_DESTROYED, ("mtx_lock_spin() of destroyed mutex @ %s:%d", file, line)); KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin, ("mtx_lock_spin() of sleep mutex %s @ %s:%d", m->lock_object.lo_name, file, line)); if (mtx_owned(m)) KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0, ("mtx_lock_spin: recursed on non-recursive mutex %s @ %s:%d\n", m->lock_object.lo_name, file, line)); WITNESS_CHECKORDER(&m->lock_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL); _get_spin_lock(m, curthread, opts, file, line); LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file, line); WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line); } void _mtx_unlock_spin_flags(struct mtx *m, int opts, const char *file, int line) { MPASS(curthread != NULL); KASSERT(m->mtx_lock != MTX_DESTROYED, ("mtx_unlock_spin() of destroyed mutex @ %s:%d", file, line)); KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin, ("mtx_unlock_spin() of sleep mutex %s @ %s:%d", m->lock_object.lo_name, file, line)); WITNESS_UNLOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line); LOCK_LOG_LOCK("UNLOCK", &m->lock_object, opts, m->mtx_recurse, file, line); mtx_assert(m, MA_OWNED); _rel_spin_lock(m); } /* * The important part of mtx_trylock{,_flags}() * Tries to acquire lock `m.' If this function is called on a mutex that * is already owned, it will recursively acquire the lock. */ int _mtx_trylock(struct mtx *m, int opts, const char *file, int line) { #ifdef LOCK_PROFILING uint64_t waittime = 0; int contested = 0; #endif int rval; MPASS(curthread != NULL); KASSERT(m->mtx_lock != MTX_DESTROYED, ("mtx_trylock() of destroyed mutex @ %s:%d", file, line)); KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep, ("mtx_trylock() of spin mutex %s @ %s:%d", m->lock_object.lo_name, file, line)); if (mtx_owned(m) && (m->lock_object.lo_flags & LO_RECURSABLE) != 0) { m->mtx_recurse++; atomic_set_ptr(&m->mtx_lock, MTX_RECURSED); rval = 1; } else rval = _obtain_lock(m, (uintptr_t)curthread); LOCK_LOG_TRY("LOCK", &m->lock_object, opts, rval, file, line); if (rval) { WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE | LOP_TRYLOCK, file, line); curthread->td_locks++; if (m->mtx_recurse == 0) LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_LOCK_ACQUIRE, m, contested, waittime, file, line); } return (rval); } /* * _mtx_lock_sleep: the tougher part of acquiring an MTX_DEF lock. * * We call this if the lock is either contested (i.e. we need to go to * sleep waiting for it), or if we need to recurse on it. */ void _mtx_lock_sleep(struct mtx *m, uintptr_t tid, int opts, const char *file, int line) { struct turnstile *ts; uintptr_t v; #ifdef ADAPTIVE_MUTEXES volatile struct thread *owner; #endif #ifdef KTR int cont_logged = 0; #endif #ifdef LOCK_PROFILING int contested = 0; uint64_t waittime = 0; #endif #ifdef KDTRACE_HOOKS uint64_t spin_cnt = 0; uint64_t sleep_cnt = 0; int64_t sleep_time = 0; #endif if (mtx_owned(m)) { KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0, ("_mtx_lock_sleep: recursed on non-recursive mutex %s @ %s:%d\n", m->lock_object.lo_name, file, line)); m->mtx_recurse++; atomic_set_ptr(&m->mtx_lock, MTX_RECURSED); if (LOCK_LOG_TEST(&m->lock_object, opts)) CTR1(KTR_LOCK, "_mtx_lock_sleep: %p recursing", m); return; } lock_profile_obtain_lock_failed(&m->lock_object, &contested, &waittime); if (LOCK_LOG_TEST(&m->lock_object, opts)) CTR4(KTR_LOCK, "_mtx_lock_sleep: %s contested (lock=%p) at %s:%d", m->lock_object.lo_name, (void *)m->mtx_lock, file, line); while (!_obtain_lock(m, tid)) { #ifdef KDTRACE_HOOKS spin_cnt++; #endif #ifdef ADAPTIVE_MUTEXES /* * If the owner is running on another CPU, spin until the * owner stops running or the state of the lock changes. */ v = m->mtx_lock; if (v != MTX_UNOWNED) { owner = (struct thread *)(v & ~MTX_FLAGMASK); if (TD_IS_RUNNING(owner)) { if (LOCK_LOG_TEST(&m->lock_object, 0)) CTR3(KTR_LOCK, "%s: spinning on %p held by %p", __func__, m, owner); while (mtx_owner(m) == owner && TD_IS_RUNNING(owner)) { cpu_spinwait(); #ifdef KDTRACE_HOOKS spin_cnt++; #endif } continue; } } #endif ts = turnstile_trywait(&m->lock_object); v = m->mtx_lock; /* * Check if the lock has been released while spinning for * the turnstile chain lock. */ if (v == MTX_UNOWNED) { turnstile_cancel(ts); cpu_spinwait(); continue; } #ifdef ADAPTIVE_MUTEXES /* - * If the current owner of the lock is executing on another - * CPU quit the hard path and try to spin. + * The current lock owner might have started executing + * on another CPU (or the lock could have changed + * owners) while we were waiting on the turnstile + * chain lock. If so, drop the turnstile lock and try + * again. */ owner = (struct thread *)(v & ~MTX_FLAGMASK); if (TD_IS_RUNNING(owner)) { turnstile_cancel(ts); cpu_spinwait(); continue; } #endif /* * If the mutex isn't already contested and a failure occurs * setting the contested bit, the mutex was either released * or the state of the MTX_RECURSED bit changed. */ if ((v & MTX_CONTESTED) == 0 && !atomic_cmpset_ptr(&m->mtx_lock, v, v | MTX_CONTESTED)) { turnstile_cancel(ts); cpu_spinwait(); continue; } /* * We definitely must sleep for this lock. */ mtx_assert(m, MA_NOTOWNED); #ifdef KTR if (!cont_logged) { CTR6(KTR_CONTENTION, "contention: %p at %s:%d wants %s, taken by %s:%d", (void *)tid, file, line, m->lock_object.lo_name, WITNESS_FILE(&m->lock_object), WITNESS_LINE(&m->lock_object)); cont_logged = 1; } #endif /* * Block on the turnstile. */ #ifdef KDTRACE_HOOKS sleep_time -= lockstat_nsecs(); #endif turnstile_wait(ts, mtx_owner(m), TS_EXCLUSIVE_QUEUE); #ifdef KDTRACE_HOOKS sleep_time += lockstat_nsecs(); sleep_cnt++; #endif } #ifdef KTR if (cont_logged) { CTR4(KTR_CONTENTION, "contention end: %s acquired by %p at %s:%d", m->lock_object.lo_name, (void *)tid, file, line); } #endif LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_LOCK_ACQUIRE, m, contested, waittime, file, line); #ifdef KDTRACE_HOOKS if (sleep_time) LOCKSTAT_RECORD1(LS_MTX_LOCK_BLOCK, m, sleep_time); /* * Only record the loops spinning and not sleeping. */ if (spin_cnt > sleep_cnt) LOCKSTAT_RECORD1(LS_MTX_LOCK_SPIN, m, (spin_cnt - sleep_cnt)); #endif } static void _mtx_lock_spin_failed(struct mtx *m) { struct thread *td; td = mtx_owner(m); /* If the mutex is unlocked, try again. */ if (td == NULL) return; printf( "spin lock %p (%s) held by %p (tid %d) too long\n", m, m->lock_object.lo_name, td, td->td_tid); #ifdef WITNESS witness_display_spinlock(&m->lock_object, td); #endif panic("spin lock held too long"); } #ifdef SMP /* * _mtx_lock_spin: the tougher part of acquiring an MTX_SPIN lock. * * This is only called if we need to actually spin for the lock. Recursion * is handled inline. */ void _mtx_lock_spin(struct mtx *m, uintptr_t tid, int opts, const char *file, int line) { int i = 0; #ifdef LOCK_PROFILING int contested = 0; uint64_t waittime = 0; #endif if (LOCK_LOG_TEST(&m->lock_object, opts)) CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m); lock_profile_obtain_lock_failed(&m->lock_object, &contested, &waittime); while (!_obtain_lock(m, tid)) { /* Give interrupts a chance while we spin. */ spinlock_exit(); while (m->mtx_lock != MTX_UNOWNED) { if (i++ < 10000000) { cpu_spinwait(); continue; } if (i < 60000000 || kdb_active || panicstr != NULL) DELAY(1); else _mtx_lock_spin_failed(m); cpu_spinwait(); } spinlock_enter(); } if (LOCK_LOG_TEST(&m->lock_object, opts)) CTR1(KTR_LOCK, "_mtx_lock_spin: %p spin done", m); LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_SPIN_LOCK_ACQUIRE, m, contested, waittime, (file), (line)); LOCKSTAT_RECORD1(LS_MTX_SPIN_LOCK_SPIN, m, i); } #endif /* SMP */ void _thread_lock_flags(struct thread *td, int opts, const char *file, int line) { struct mtx *m; uintptr_t tid; int i; #ifdef LOCK_PROFILING int contested = 0; uint64_t waittime = 0; #endif #ifdef KDTRACE_HOOKS uint64_t spin_cnt = 0; #endif i = 0; tid = (uintptr_t)curthread; for (;;) { retry: spinlock_enter(); m = td->td_lock; KASSERT(m->mtx_lock != MTX_DESTROYED, ("thread_lock() of destroyed mutex @ %s:%d", file, line)); KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin, ("thread_lock() of sleep mutex %s @ %s:%d", m->lock_object.lo_name, file, line)); if (mtx_owned(m)) KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0, ("thread_lock: recursed on non-recursive mutex %s @ %s:%d\n", m->lock_object.lo_name, file, line)); WITNESS_CHECKORDER(&m->lock_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL); while (!_obtain_lock(m, tid)) { #ifdef KDTRACE_HOOKS spin_cnt++; #endif if (m->mtx_lock == tid) { m->mtx_recurse++; break; } lock_profile_obtain_lock_failed(&m->lock_object, &contested, &waittime); /* Give interrupts a chance while we spin. */ spinlock_exit(); while (m->mtx_lock != MTX_UNOWNED) { if (i++ < 10000000) cpu_spinwait(); else if (i < 60000000 || kdb_active || panicstr != NULL) DELAY(1); else _mtx_lock_spin_failed(m); cpu_spinwait(); if (m != td->td_lock) goto retry; } spinlock_enter(); } if (m == td->td_lock) break; _rel_spin_lock(m); /* does spinlock_exit() */ #ifdef KDTRACE_HOOKS spin_cnt++; #endif } if (m->mtx_recurse == 0) LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_SPIN_LOCK_ACQUIRE, m, contested, waittime, (file), (line)); LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file, line); WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line); LOCKSTAT_RECORD1(LS_THREAD_LOCK_SPIN, m, spin_cnt); } struct mtx * thread_lock_block(struct thread *td) { struct mtx *lock; spinlock_enter(); THREAD_LOCK_ASSERT(td, MA_OWNED); lock = td->td_lock; td->td_lock = &blocked_lock; mtx_unlock_spin(lock); return (lock); } void thread_lock_unblock(struct thread *td, struct mtx *new) { mtx_assert(new, MA_OWNED); MPASS(td->td_lock == &blocked_lock); atomic_store_rel_ptr((volatile void *)&td->td_lock, (uintptr_t)new); spinlock_exit(); } void thread_lock_set(struct thread *td, struct mtx *new) { struct mtx *lock; mtx_assert(new, MA_OWNED); THREAD_LOCK_ASSERT(td, MA_OWNED); lock = td->td_lock; td->td_lock = new; mtx_unlock_spin(lock); } /* * _mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock. * * We are only called here if the lock is recursed or contested (i.e. we * need to wake up a blocked thread). */ void _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line) { struct turnstile *ts; if (mtx_recursed(m)) { if (--(m->mtx_recurse) == 0) atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED); if (LOCK_LOG_TEST(&m->lock_object, opts)) CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p unrecurse", m); return; } /* * We have to lock the chain before the turnstile so this turnstile * can be removed from the hash list if it is empty. */ turnstile_chain_lock(&m->lock_object); ts = turnstile_lookup(&m->lock_object); if (LOCK_LOG_TEST(&m->lock_object, opts)) CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m); MPASS(ts != NULL); turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE); _release_lock_quick(m); /* * This turnstile is now no longer associated with the mutex. We can * unlock the chain lock so a new turnstile may take it's place. */ turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); turnstile_chain_unlock(&m->lock_object); } /* * All the unlocking of MTX_SPIN locks is done inline. * See the _rel_spin_lock() macro for the details. */ /* * The backing function for the INVARIANTS-enabled mtx_assert() */ #ifdef INVARIANT_SUPPORT void _mtx_assert(struct mtx *m, int what, const char *file, int line) { if (panicstr != NULL || dumping) return; switch (what) { case MA_OWNED: case MA_OWNED | MA_RECURSED: case MA_OWNED | MA_NOTRECURSED: if (!mtx_owned(m)) panic("mutex %s not owned at %s:%d", m->lock_object.lo_name, file, line); if (mtx_recursed(m)) { if ((what & MA_NOTRECURSED) != 0) panic("mutex %s recursed at %s:%d", m->lock_object.lo_name, file, line); } else if ((what & MA_RECURSED) != 0) { panic("mutex %s unrecursed at %s:%d", m->lock_object.lo_name, file, line); } break; case MA_NOTOWNED: if (mtx_owned(m)) panic("mutex %s owned at %s:%d", m->lock_object.lo_name, file, line); break; default: panic("unknown mtx_assert at %s:%d", file, line); } } #endif /* * The MUTEX_DEBUG-enabled mtx_validate() * * Most of these checks have been moved off into the LO_INITIALIZED flag * maintained by the witness code. */ #ifdef MUTEX_DEBUG void mtx_validate(struct mtx *); void mtx_validate(struct mtx *m) { /* * XXX: When kernacc() does not require Giant we can reenable this check */ #ifdef notyet /* * Can't call kernacc() from early init386(), especially when * initializing Giant mutex, because some stuff in kernacc() * requires Giant itself. */ if (!cold) if (!kernacc((caddr_t)m, sizeof(m), VM_PROT_READ | VM_PROT_WRITE)) panic("Can't read and write to mutex %p", m); #endif } #endif /* * General init routine used by the MTX_SYSINIT() macro. */ void mtx_sysinit(void *arg) { struct mtx_args *margs = arg; mtx_init(margs->ma_mtx, margs->ma_desc, NULL, margs->ma_opts); } /* * Mutex initialization routine; initialize lock `m' of type contained in * `opts' with options contained in `opts' and name `name.' The optional * lock type `type' is used as a general lock category name for use with * witness. */ void mtx_init(struct mtx *m, const char *name, const char *type, int opts) { struct lock_class *class; int flags; MPASS((opts & ~(MTX_SPIN | MTX_QUIET | MTX_RECURSE | MTX_NOWITNESS | MTX_DUPOK | MTX_NOPROFILE)) == 0); #ifdef MUTEX_DEBUG /* Diagnostic and error correction */ mtx_validate(m); #endif /* Determine lock class and lock flags. */ if (opts & MTX_SPIN) class = &lock_class_mtx_spin; else class = &lock_class_mtx_sleep; flags = 0; if (opts & MTX_QUIET) flags |= LO_QUIET; if (opts & MTX_RECURSE) flags |= LO_RECURSABLE; if ((opts & MTX_NOWITNESS) == 0) flags |= LO_WITNESS; if (opts & MTX_DUPOK) flags |= LO_DUPOK; if (opts & MTX_NOPROFILE) flags |= LO_NOPROFILE; /* Initialize mutex. */ m->mtx_lock = MTX_UNOWNED; m->mtx_recurse = 0; lock_init(&m->lock_object, class, name, type, flags); } /* * Remove lock `m' from all_mtx queue. We don't allow MTX_QUIET to be * passed in as a flag here because if the corresponding mtx_init() was * called with MTX_QUIET set, then it will already be set in the mutex's * flags. */ void mtx_destroy(struct mtx *m) { if (!mtx_owned(m)) MPASS(mtx_unowned(m)); else { MPASS((m->mtx_lock & (MTX_RECURSED|MTX_CONTESTED)) == 0); /* Perform the non-mtx related part of mtx_unlock_spin(). */ if (LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin) spinlock_exit(); else curthread->td_locks--; lock_profile_release_lock(&m->lock_object); /* Tell witness this isn't locked to make it happy. */ WITNESS_UNLOCK(&m->lock_object, LOP_EXCLUSIVE, __FILE__, __LINE__); } m->mtx_lock = MTX_DESTROYED; lock_destroy(&m->lock_object); } /* * Intialize the mutex code and system mutexes. This is called from the MD * startup code prior to mi_startup(). The per-CPU data space needs to be * setup before this is called. */ void mutex_init(void) { /* Setup turnstiles so that sleep mutexes work. */ init_turnstiles(); /* * Initialize mutexes. */ mtx_init(&Giant, "Giant", NULL, MTX_DEF | MTX_RECURSE); mtx_init(&blocked_lock, "blocked lock", NULL, MTX_SPIN); blocked_lock.mtx_lock = 0xdeadc0de; /* Always blocked. */ mtx_init(&proc0.p_mtx, "process lock", NULL, MTX_DEF | MTX_DUPOK); mtx_init(&proc0.p_slock, "process slock", NULL, MTX_SPIN | MTX_RECURSE); mtx_init(&devmtx, "cdev", NULL, MTX_DEF); mtx_lock(&Giant); } #ifdef DDB void db_show_mtx(struct lock_object *lock) { struct thread *td; struct mtx *m; m = (struct mtx *)lock; db_printf(" flags: {"); if (LOCK_CLASS(lock) == &lock_class_mtx_spin) db_printf("SPIN"); else db_printf("DEF"); if (m->lock_object.lo_flags & LO_RECURSABLE) db_printf(", RECURSE"); if (m->lock_object.lo_flags & LO_DUPOK) db_printf(", DUPOK"); db_printf("}\n"); db_printf(" state: {"); if (mtx_unowned(m)) db_printf("UNOWNED"); else if (mtx_destroyed(m)) db_printf("DESTROYED"); else { db_printf("OWNED"); if (m->mtx_lock & MTX_CONTESTED) db_printf(", CONTESTED"); if (m->mtx_lock & MTX_RECURSED) db_printf(", RECURSED"); } db_printf("}\n"); if (!mtx_unowned(m) && !mtx_destroyed(m)) { td = mtx_owner(m); db_printf(" owner: %p (tid %d, pid %d, \"%s\")\n", td, td->td_tid, td->td_proc->p_pid, td->td_name); if (mtx_recursed(m)) db_printf(" recursed: %d\n", m->mtx_recurse); } } #endif Index: head/sys/kern/kern_rwlock.c =================================================================== --- head/sys/kern/kern_rwlock.c (revision 193034) +++ head/sys/kern/kern_rwlock.c (revision 193035) @@ -1,1124 +1,1130 @@ /*- * Copyright (c) 2006 John Baldwin * 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. Neither the name of the author nor the names of any co-contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ /* * Machine independent bits of reader/writer lock implementation. */ #include __FBSDID("$FreeBSD$"); #include "opt_ddb.h" #include "opt_kdtrace.h" #include "opt_no_adaptive_rwlocks.h" #include #include #include #include #include #include #include #include #include #include #include CTASSERT((RW_RECURSE & LO_CLASSFLAGS) == RW_RECURSE); #if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS) #define ADAPTIVE_RWLOCKS #endif #ifdef ADAPTIVE_RWLOCKS static int rowner_retries = 10; static int rowner_loops = 10000; SYSCTL_NODE(_debug, OID_AUTO, rwlock, CTLFLAG_RD, NULL, "rwlock debugging"); SYSCTL_INT(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, ""); SYSCTL_INT(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, ""); #endif #ifdef DDB #include static void db_show_rwlock(struct lock_object *lock); #endif static void assert_rw(struct lock_object *lock, int what); static void lock_rw(struct lock_object *lock, int how); #ifdef KDTRACE_HOOKS static int owner_rw(struct lock_object *lock, struct thread **owner); #endif static int unlock_rw(struct lock_object *lock); struct lock_class lock_class_rw = { .lc_name = "rw", .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE, .lc_assert = assert_rw, #ifdef DDB .lc_ddb_show = db_show_rwlock, #endif .lc_lock = lock_rw, .lc_unlock = unlock_rw, #ifdef KDTRACE_HOOKS .lc_owner = owner_rw, #endif }; /* * Return a pointer to the owning thread if the lock is write-locked or * NULL if the lock is unlocked or read-locked. */ #define rw_wowner(rw) \ ((rw)->rw_lock & RW_LOCK_READ ? NULL : \ (struct thread *)RW_OWNER((rw)->rw_lock)) /* * Returns if a write owner is recursed. Write ownership is not assured * here and should be previously checked. */ #define rw_recursed(rw) ((rw)->rw_recurse != 0) /* * Return true if curthread helds the lock. */ #define rw_wlocked(rw) (rw_wowner((rw)) == curthread) /* * Return a pointer to the owning thread for this lock who should receive * any priority lent by threads that block on this lock. Currently this * is identical to rw_wowner(). */ #define rw_owner(rw) rw_wowner(rw) #ifndef INVARIANTS #define _rw_assert(rw, what, file, line) #endif void assert_rw(struct lock_object *lock, int what) { rw_assert((struct rwlock *)lock, what); } void lock_rw(struct lock_object *lock, int how) { struct rwlock *rw; rw = (struct rwlock *)lock; if (how) rw_wlock(rw); else rw_rlock(rw); } int unlock_rw(struct lock_object *lock) { struct rwlock *rw; rw = (struct rwlock *)lock; rw_assert(rw, RA_LOCKED | LA_NOTRECURSED); if (rw->rw_lock & RW_LOCK_READ) { rw_runlock(rw); return (0); } else { rw_wunlock(rw); return (1); } } #ifdef KDTRACE_HOOKS int owner_rw(struct lock_object *lock, struct thread **owner) { struct rwlock *rw = (struct rwlock *)lock; uintptr_t x = rw->rw_lock; *owner = rw_wowner(rw); return ((x & RW_LOCK_READ) != 0 ? (RW_READERS(x) != 0) : (*owner != NULL)); } #endif void rw_init_flags(struct rwlock *rw, const char *name, int opts) { int flags; MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET | RW_RECURSE)) == 0); flags = LO_UPGRADABLE | LO_RECURSABLE; if (opts & RW_DUPOK) flags |= LO_DUPOK; if (opts & RW_NOPROFILE) flags |= LO_NOPROFILE; if (!(opts & RW_NOWITNESS)) flags |= LO_WITNESS; if (opts & RW_QUIET) flags |= LO_QUIET; flags |= opts & RW_RECURSE; rw->rw_lock = RW_UNLOCKED; rw->rw_recurse = 0; lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags); } void rw_destroy(struct rwlock *rw) { KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock not unlocked")); KASSERT(rw->rw_recurse == 0, ("rw lock still recursed")); rw->rw_lock = RW_DESTROYED; lock_destroy(&rw->lock_object); } void rw_sysinit(void *arg) { struct rw_args *args = arg; rw_init(args->ra_rw, args->ra_desc); } void rw_sysinit_flags(void *arg) { struct rw_args_flags *args = arg; rw_init_flags(args->ra_rw, args->ra_desc, args->ra_flags); } int rw_wowned(struct rwlock *rw) { return (rw_wowner(rw) == curthread); } void _rw_wlock(struct rwlock *rw, const char *file, int line) { MPASS(curthread != NULL); KASSERT(rw->rw_lock != RW_DESTROYED, ("rw_wlock() of destroyed rwlock @ %s:%d", file, line)); WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL); __rw_wlock(rw, curthread, file, line); LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line); WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); curthread->td_locks++; } int _rw_try_wlock(struct rwlock *rw, const char *file, int line) { int rval; KASSERT(rw->rw_lock != RW_DESTROYED, ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line)); if (rw_wlocked(rw) && (rw->lock_object.lo_flags & RW_RECURSE) != 0) { rw->rw_recurse++; rval = 1; } else rval = atomic_cmpset_acq_ptr(&rw->rw_lock, RW_UNLOCKED, (uintptr_t)curthread); LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line); if (rval) { WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, file, line); curthread->td_locks++; } return (rval); } void _rw_wunlock(struct rwlock *rw, const char *file, int line) { MPASS(curthread != NULL); KASSERT(rw->rw_lock != RW_DESTROYED, ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line)); _rw_assert(rw, RA_WLOCKED, file, line); curthread->td_locks--; WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line); if (!rw_recursed(rw)) LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_WUNLOCK_RELEASE, rw); __rw_wunlock(rw, curthread, file, line); } /* * Determines whether a new reader can acquire a lock. Succeeds if the * reader already owns a read lock and the lock is locked for read to * prevent deadlock from reader recursion. Also succeeds if the lock * is unlocked and has no writer waiters or spinners. Failing otherwise * prioritizes writers before readers. */ #define RW_CAN_READ(_rw) \ ((curthread->td_rw_rlocks && (_rw) & RW_LOCK_READ) || ((_rw) & \ (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) == \ RW_LOCK_READ) void _rw_rlock(struct rwlock *rw, const char *file, int line) { struct turnstile *ts; #ifdef ADAPTIVE_RWLOCKS volatile struct thread *owner; int spintries = 0; int i; #endif #ifdef LOCK_PROFILING uint64_t waittime = 0; int contested = 0; #endif uintptr_t v; #ifdef KDTRACE_HOOKS uint64_t spin_cnt = 0; uint64_t sleep_cnt = 0; int64_t sleep_time = 0; #endif KASSERT(rw->rw_lock != RW_DESTROYED, ("rw_rlock() of destroyed rwlock @ %s:%d", file, line)); KASSERT(rw_wowner(rw) != curthread, ("%s (%s): wlock already held @ %s:%d", __func__, rw->lock_object.lo_name, file, line)); WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL); for (;;) { #ifdef KDTRACE_HOOKS spin_cnt++; #endif /* * Handle the easy case. If no other thread has a write * lock, then try to bump up the count of read locks. Note * that we have to preserve the current state of the * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a * read lock, then rw_lock must have changed, so restart * the loop. Note that this handles the case of a * completely unlocked rwlock since such a lock is encoded * as a read lock with no waiters. */ v = rw->rw_lock; if (RW_CAN_READ(v)) { /* * The RW_LOCK_READ_WAITERS flag should only be set * if the lock has been unlocked and write waiters * were present. */ if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, v + RW_ONE_READER)) { if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR4(KTR_LOCK, "%s: %p succeed %p -> %p", __func__, rw, (void *)v, (void *)(v + RW_ONE_READER)); break; } cpu_spinwait(); continue; } lock_profile_obtain_lock_failed(&rw->lock_object, &contested, &waittime); #ifdef ADAPTIVE_RWLOCKS /* * If the owner is running on another CPU, spin until * the owner stops running or the state of the lock * changes. */ if ((v & RW_LOCK_READ) == 0) { owner = (struct thread *)RW_OWNER(v); if (TD_IS_RUNNING(owner)) { if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR3(KTR_LOCK, "%s: spinning on %p held by %p", __func__, rw, owner); while ((struct thread*)RW_OWNER(rw->rw_lock) == owner && TD_IS_RUNNING(owner)) { cpu_spinwait(); #ifdef KDTRACE_HOOKS spin_cnt++; #endif } continue; } } else if (spintries < rowner_retries) { spintries++; for (i = 0; i < rowner_loops; i++) { v = rw->rw_lock; if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(v)) break; cpu_spinwait(); } if (i != rowner_loops) continue; } #endif /* * Okay, now it's the hard case. Some other thread already * has a write lock or there are write waiters present, * acquire the turnstile lock so we can begin the process * of blocking. */ ts = turnstile_trywait(&rw->lock_object); /* * The lock might have been released while we spun, so * recheck its state and restart the loop if needed. */ v = rw->rw_lock; if (RW_CAN_READ(v)) { turnstile_cancel(ts); cpu_spinwait(); continue; } #ifdef ADAPTIVE_RWLOCKS /* - * If the current owner of the lock is executing on another - * CPU quit the hard path and try to spin. + * The current lock owner might have started executing + * on another CPU (or the lock could have changed + * owners) while we were waiting on the turnstile + * chain lock. If so, drop the turnstile lock and try + * again. */ if ((v & RW_LOCK_READ) == 0) { owner = (struct thread *)RW_OWNER(v); if (TD_IS_RUNNING(owner)) { turnstile_cancel(ts); cpu_spinwait(); continue; } } #endif /* * The lock is held in write mode or it already has waiters. */ MPASS(!RW_CAN_READ(v)); /* * If the RW_LOCK_READ_WAITERS flag is already set, then * we can go ahead and block. If it is not set then try * to set it. If we fail to set it drop the turnstile * lock and restart the loop. */ if (!(v & RW_LOCK_READ_WAITERS)) { if (!atomic_cmpset_ptr(&rw->rw_lock, v, v | RW_LOCK_READ_WAITERS)) { turnstile_cancel(ts); cpu_spinwait(); continue; } if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p set read waiters flag", __func__, rw); } /* * We were unable to acquire the lock and the read waiters * flag is set, so we must block on the turnstile. */ if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, rw); #ifdef KDTRACE_HOOKS sleep_time -= lockstat_nsecs(); #endif turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE); #ifdef KDTRACE_HOOKS sleep_time += lockstat_nsecs(); sleep_cnt++; #endif if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p resuming from turnstile", __func__, rw); } /* * TODO: acquire "owner of record" here. Here be turnstile dragons * however. turnstiles don't like owners changing between calls to * turnstile_wait() currently. */ LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_RLOCK_ACQUIRE, rw, contested, waittime, file, line); LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line); WITNESS_LOCK(&rw->lock_object, 0, file, line); curthread->td_locks++; curthread->td_rw_rlocks++; #ifdef KDTRACE_HOOKS if (sleep_time) LOCKSTAT_RECORD1(LS_RW_RLOCK_BLOCK, rw, sleep_time); /* * Record only the loops spinning and not sleeping. */ if (spin_cnt > sleep_cnt) LOCKSTAT_RECORD1(LS_RW_RLOCK_SPIN, rw, (spin_cnt - sleep_cnt)); #endif } int _rw_try_rlock(struct rwlock *rw, const char *file, int line) { uintptr_t x; for (;;) { x = rw->rw_lock; KASSERT(rw->rw_lock != RW_DESTROYED, ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line)); if (!(x & RW_LOCK_READ)) break; if (atomic_cmpset_acq_ptr(&rw->rw_lock, x, x + RW_ONE_READER)) { LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file, line); WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line); curthread->td_locks++; curthread->td_rw_rlocks++; return (1); } } LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line); return (0); } void _rw_runlock(struct rwlock *rw, const char *file, int line) { struct turnstile *ts; uintptr_t x, v, queue; KASSERT(rw->rw_lock != RW_DESTROYED, ("rw_runlock() of destroyed rwlock @ %s:%d", file, line)); _rw_assert(rw, RA_RLOCKED, file, line); curthread->td_locks--; curthread->td_rw_rlocks--; WITNESS_UNLOCK(&rw->lock_object, 0, file, line); LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line); /* TODO: drop "owner of record" here. */ for (;;) { /* * See if there is more than one read lock held. If so, * just drop one and return. */ x = rw->rw_lock; if (RW_READERS(x) > 1) { if (atomic_cmpset_ptr(&rw->rw_lock, x, x - RW_ONE_READER)) { if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR4(KTR_LOCK, "%s: %p succeeded %p -> %p", __func__, rw, (void *)x, (void *)(x - RW_ONE_READER)); break; } continue; } /* * If there aren't any waiters for a write lock, then try * to drop it quickly. */ if (!(x & RW_LOCK_WAITERS)) { MPASS((x & ~RW_LOCK_WRITE_SPINNER) == RW_READERS_LOCK(1)); if (atomic_cmpset_ptr(&rw->rw_lock, x, RW_UNLOCKED)) { if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p last succeeded", __func__, rw); break; } continue; } /* * Ok, we know we have waiters and we think we are the * last reader, so grab the turnstile lock. */ turnstile_chain_lock(&rw->lock_object); v = rw->rw_lock & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER); MPASS(v & RW_LOCK_WAITERS); /* * Try to drop our lock leaving the lock in a unlocked * state. * * If you wanted to do explicit lock handoff you'd have to * do it here. You'd also want to use turnstile_signal() * and you'd have to handle the race where a higher * priority thread blocks on the write lock before the * thread you wakeup actually runs and have the new thread * "steal" the lock. For now it's a lot simpler to just * wakeup all of the waiters. * * As above, if we fail, then another thread might have * acquired a read lock, so drop the turnstile lock and * restart. */ x = RW_UNLOCKED; if (v & RW_LOCK_WRITE_WAITERS) { queue = TS_EXCLUSIVE_QUEUE; x |= (v & RW_LOCK_READ_WAITERS); } else queue = TS_SHARED_QUEUE; if (!atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v, x)) { turnstile_chain_unlock(&rw->lock_object); continue; } if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p last succeeded with waiters", __func__, rw); /* * Ok. The lock is released and all that's left is to * wake up the waiters. Note that the lock might not be * free anymore, but in that case the writers will just * block again if they run before the new lock holder(s) * release the lock. */ ts = turnstile_lookup(&rw->lock_object); MPASS(ts != NULL); turnstile_broadcast(ts, queue); turnstile_unpend(ts, TS_SHARED_LOCK); turnstile_chain_unlock(&rw->lock_object); break; } LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_RUNLOCK_RELEASE, rw); } /* * This function is called when we are unable to obtain a write lock on the * first try. This means that at least one other thread holds either a * read or write lock. */ void _rw_wlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line) { struct turnstile *ts; #ifdef ADAPTIVE_RWLOCKS volatile struct thread *owner; int spintries = 0; int i; #endif uintptr_t v, x; #ifdef LOCK_PROFILING uint64_t waittime = 0; int contested = 0; #endif #ifdef KDTRACE_HOOKS uint64_t spin_cnt = 0; uint64_t sleep_cnt = 0; int64_t sleep_time = 0; #endif if (rw_wlocked(rw)) { KASSERT(rw->lock_object.lo_flags & RW_RECURSE, ("%s: recursing but non-recursive rw %s @ %s:%d\n", __func__, rw->lock_object.lo_name, file, line)); rw->rw_recurse++; if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw); return; } if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, rw->lock_object.lo_name, (void *)rw->rw_lock, file, line); while (!_rw_write_lock(rw, tid)) { #ifdef KDTRACE_HOOKS spin_cnt++; #endif lock_profile_obtain_lock_failed(&rw->lock_object, &contested, &waittime); #ifdef ADAPTIVE_RWLOCKS /* * 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. */ v = rw->rw_lock; owner = (struct thread *)RW_OWNER(v); if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) { if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR3(KTR_LOCK, "%s: spinning on %p held by %p", __func__, rw, owner); while ((struct thread*)RW_OWNER(rw->rw_lock) == owner && TD_IS_RUNNING(owner)) { cpu_spinwait(); #ifdef KDTRACE_HOOKS spin_cnt++; #endif } continue; } if ((v & RW_LOCK_READ) && RW_READERS(v) && spintries < rowner_retries) { if (!(v & RW_LOCK_WRITE_SPINNER)) { if (!atomic_cmpset_ptr(&rw->rw_lock, v, v | RW_LOCK_WRITE_SPINNER)) { cpu_spinwait(); continue; } } spintries++; for (i = 0; i < rowner_loops; i++) { if ((rw->rw_lock & RW_LOCK_WRITE_SPINNER) == 0) break; cpu_spinwait(); } #ifdef KDTRACE_HOOKS spin_cnt += rowner_loops - i; #endif if (i != rowner_loops) continue; } #endif ts = turnstile_trywait(&rw->lock_object); v = rw->rw_lock; #ifdef ADAPTIVE_RWLOCKS /* - * If the current owner of the lock is executing on another - * CPU quit the hard path and try to spin. + * The current lock owner might have started executing + * on another CPU (or the lock could have changed + * owners) while we were waiting on the turnstile + * chain lock. If so, drop the turnstile lock and try + * again. */ if (!(v & RW_LOCK_READ)) { owner = (struct thread *)RW_OWNER(v); if (TD_IS_RUNNING(owner)) { turnstile_cancel(ts); cpu_spinwait(); continue; } } #endif /* * Check for the waiters flags about this rwlock. * If the lock was released, without maintain any pending * waiters queue, simply try to acquire it. * If a pending waiters queue is present, claim the lock * ownership and maintain the pending queue. */ x = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER); if ((v & ~x) == RW_UNLOCKED) { x &= ~RW_LOCK_WRITE_SPINNER; if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, tid | x)) { if (x) turnstile_claim(ts); else turnstile_cancel(ts); break; } turnstile_cancel(ts); cpu_spinwait(); continue; } /* * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to * set it. If we fail to set it, then loop back and try * again. */ if (!(v & RW_LOCK_WRITE_WAITERS)) { if (!atomic_cmpset_ptr(&rw->rw_lock, v, v | RW_LOCK_WRITE_WAITERS)) { turnstile_cancel(ts); cpu_spinwait(); continue; } if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p set write waiters flag", __func__, rw); } /* * We were unable to acquire the lock and the write waiters * flag is set, so we must block on the turnstile. */ if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, rw); #ifdef KDTRACE_HOOKS sleep_time -= lockstat_nsecs(); #endif turnstile_wait(ts, rw_owner(rw), TS_EXCLUSIVE_QUEUE); #ifdef KDTRACE_HOOKS sleep_time += lockstat_nsecs(); sleep_cnt++; #endif if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p resuming from turnstile", __func__, rw); #ifdef ADAPTIVE_RWLOCKS spintries = 0; #endif } LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_WLOCK_ACQUIRE, rw, contested, waittime, file, line); #ifdef KDTRACE_HOOKS if (sleep_time) LOCKSTAT_RECORD1(LS_RW_WLOCK_BLOCK, rw, sleep_time); /* * Record only the loops spinning and not sleeping. */ if (spin_cnt > sleep_cnt) LOCKSTAT_RECORD1(LS_RW_WLOCK_SPIN, rw, (spin_cnt - sleep_cnt)); #endif } /* * This function is called if the first try at releasing a write lock failed. * This means that one of the 2 waiter bits must be set indicating that at * least one thread is waiting on this lock. */ void _rw_wunlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line) { struct turnstile *ts; uintptr_t v; int queue; if (rw_wlocked(rw) && rw_recursed(rw)) { rw->rw_recurse--; if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw); return; } KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS), ("%s: neither of the waiter flags are set", __func__)); if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR2(KTR_LOCK, "%s: %p contested", __func__, rw); turnstile_chain_lock(&rw->lock_object); ts = turnstile_lookup(&rw->lock_object); MPASS(ts != NULL); /* * Use the same algo as sx locks for now. Prefer waking up shared * waiters if we have any over writers. This is probably not ideal. * * 'v' is the value we are going to write back to rw_lock. If we * have waiters on both queues, we need to preserve the state of * the waiter flag for the queue we don't wake up. For now this is * hardcoded for the algorithm mentioned above. * * In the case of both readers and writers waiting we wakeup the * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a * new writer comes in before a reader it will claim the lock up * above. There is probably a potential priority inversion in * there that could be worked around either by waking both queues * of waiters or doing some complicated lock handoff gymnastics. */ v = RW_UNLOCKED; if (rw->rw_lock & RW_LOCK_WRITE_WAITERS) { queue = TS_EXCLUSIVE_QUEUE; v |= (rw->rw_lock & RW_LOCK_READ_WAITERS); } else queue = TS_SHARED_QUEUE; /* Wake up all waiters for the specific queue. */ if (LOCK_LOG_TEST(&rw->lock_object, 0)) CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw, queue == TS_SHARED_QUEUE ? "read" : "write"); turnstile_broadcast(ts, queue); atomic_store_rel_ptr(&rw->rw_lock, v); turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); turnstile_chain_unlock(&rw->lock_object); } /* * Attempt to do a non-blocking upgrade from a read lock to a write * lock. This will only succeed if this thread holds a single read * lock. Returns true if the upgrade succeeded and false otherwise. */ int _rw_try_upgrade(struct rwlock *rw, const char *file, int line) { uintptr_t v, x, tid; struct turnstile *ts; int success; KASSERT(rw->rw_lock != RW_DESTROYED, ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line)); _rw_assert(rw, RA_RLOCKED, file, line); /* * Attempt to switch from one reader to a writer. If there * are any write waiters, then we will have to lock the * turnstile first to prevent races with another writer * calling turnstile_wait() before we have claimed this * turnstile. So, do the simple case of no waiters first. */ tid = (uintptr_t)curthread; success = 0; for (;;) { v = rw->rw_lock; if (RW_READERS(v) > 1) break; if (!(v & RW_LOCK_WAITERS)) { success = atomic_cmpset_ptr(&rw->rw_lock, v, tid); if (!success) continue; break; } /* * Ok, we think we have waiters, so lock the turnstile. */ ts = turnstile_trywait(&rw->lock_object); v = rw->rw_lock; if (RW_READERS(v) > 1) { turnstile_cancel(ts); break; } /* * Try to switch from one reader to a writer again. This time * we honor the current state of the waiters flags. * If we obtain the lock with the flags set, then claim * ownership of the turnstile. */ x = rw->rw_lock & RW_LOCK_WAITERS; success = atomic_cmpset_ptr(&rw->rw_lock, v, tid | x); if (success) { if (x) turnstile_claim(ts); else turnstile_cancel(ts); break; } turnstile_cancel(ts); } LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line); if (success) { curthread->td_rw_rlocks--; WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, file, line); LOCKSTAT_RECORD0(LS_RW_TRYUPGRADE_UPGRADE, rw); } return (success); } /* * Downgrade a write lock into a single read lock. */ void _rw_downgrade(struct rwlock *rw, const char *file, int line) { struct turnstile *ts; uintptr_t tid, v; int rwait, wwait; KASSERT(rw->rw_lock != RW_DESTROYED, ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line)); _rw_assert(rw, RA_WLOCKED | RA_NOTRECURSED, file, line); #ifndef INVARIANTS if (rw_recursed(rw)) panic("downgrade of a recursed lock"); #endif WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line); /* * Convert from a writer to a single reader. First we handle * the easy case with no waiters. If there are any waiters, we * lock the turnstile and "disown" the lock. */ tid = (uintptr_t)curthread; if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1))) goto out; /* * Ok, we think we have waiters, so lock the turnstile so we can * read the waiter flags without any races. */ turnstile_chain_lock(&rw->lock_object); v = rw->rw_lock & RW_LOCK_WAITERS; rwait = v & RW_LOCK_READ_WAITERS; wwait = v & RW_LOCK_WRITE_WAITERS; MPASS(rwait | wwait); /* * Downgrade from a write lock while preserving waiters flag * and give up ownership of the turnstile. */ ts = turnstile_lookup(&rw->lock_object); MPASS(ts != NULL); if (!wwait) v &= ~RW_LOCK_READ_WAITERS; atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v); /* * Wake other readers if there are no writers pending. Otherwise they * won't be able to acquire the lock anyway. */ if (rwait && !wwait) { turnstile_broadcast(ts, TS_SHARED_QUEUE); turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); } else turnstile_disown(ts); turnstile_chain_unlock(&rw->lock_object); out: curthread->td_rw_rlocks++; LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line); LOCKSTAT_RECORD0(LS_RW_DOWNGRADE_DOWNGRADE, rw); } #ifdef INVARIANT_SUPPORT #ifndef INVARIANTS #undef _rw_assert #endif /* * In the non-WITNESS case, rw_assert() can only detect that at least * *some* thread owns an rlock, but it cannot guarantee that *this* * thread owns an rlock. */ void _rw_assert(struct rwlock *rw, int what, const char *file, int line) { if (panicstr != NULL) return; switch (what) { case RA_LOCKED: case RA_LOCKED | RA_RECURSED: case RA_LOCKED | RA_NOTRECURSED: case RA_RLOCKED: #ifdef WITNESS witness_assert(&rw->lock_object, what, file, line); #else /* * If some other thread has a write lock or we have one * and are asserting a read lock, fail. Also, if no one * has a lock at all, fail. */ if (rw->rw_lock == RW_UNLOCKED || (!(rw->rw_lock & RW_LOCK_READ) && (what == RA_RLOCKED || rw_wowner(rw) != curthread))) panic("Lock %s not %slocked @ %s:%d\n", rw->lock_object.lo_name, (what == RA_RLOCKED) ? "read " : "", file, line); if (!(rw->rw_lock & RW_LOCK_READ)) { if (rw_recursed(rw)) { if (what & RA_NOTRECURSED) panic("Lock %s recursed @ %s:%d\n", rw->lock_object.lo_name, file, line); } else if (what & RA_RECURSED) panic("Lock %s not recursed @ %s:%d\n", rw->lock_object.lo_name, file, line); } #endif break; case RA_WLOCKED: case RA_WLOCKED | RA_RECURSED: case RA_WLOCKED | RA_NOTRECURSED: if (rw_wowner(rw) != curthread) panic("Lock %s not exclusively locked @ %s:%d\n", rw->lock_object.lo_name, file, line); if (rw_recursed(rw)) { if (what & RA_NOTRECURSED) panic("Lock %s recursed @ %s:%d\n", rw->lock_object.lo_name, file, line); } else if (what & RA_RECURSED) panic("Lock %s not recursed @ %s:%d\n", rw->lock_object.lo_name, file, line); break; case RA_UNLOCKED: #ifdef WITNESS witness_assert(&rw->lock_object, what, file, line); #else /* * If we hold a write lock fail. We can't reliably check * to see if we hold a read lock or not. */ if (rw_wowner(rw) == curthread) panic("Lock %s exclusively locked @ %s:%d\n", rw->lock_object.lo_name, file, line); #endif break; default: panic("Unknown rw lock assertion: %d @ %s:%d", what, file, line); } } #endif /* INVARIANT_SUPPORT */ #ifdef DDB void db_show_rwlock(struct lock_object *lock) { struct rwlock *rw; struct thread *td; rw = (struct rwlock *)lock; db_printf(" state: "); if (rw->rw_lock == RW_UNLOCKED) db_printf("UNLOCKED\n"); else if (rw->rw_lock == RW_DESTROYED) { db_printf("DESTROYED\n"); return; } else if (rw->rw_lock & RW_LOCK_READ) db_printf("RLOCK: %ju locks\n", (uintmax_t)(RW_READERS(rw->rw_lock))); else { td = rw_wowner(rw); db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td, td->td_tid, td->td_proc->p_pid, td->td_name); if (rw_recursed(rw)) db_printf(" recursed: %u\n", rw->rw_recurse); } db_printf(" waiters: "); switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) { case RW_LOCK_READ_WAITERS: db_printf("readers\n"); break; case RW_LOCK_WRITE_WAITERS: db_printf("writers\n"); break; case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS: db_printf("readers and writers\n"); break; default: db_printf("none\n"); break; } } #endif