diff options
Diffstat (limited to 'sys/kern/kern_rwlock.c')
| -rw-r--r-- | sys/kern/kern_rwlock.c | 1229 |
1 files changed, 1229 insertions, 0 deletions
diff --git a/sys/kern/kern_rwlock.c b/sys/kern/kern_rwlock.c new file mode 100644 index 0000000..60a7faa --- /dev/null +++ b/sys/kern/kern_rwlock.c @@ -0,0 +1,1229 @@ +/*- + * Copyright (c) 2006 John Baldwin <jhb@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, 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 <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + +#include "opt_ddb.h" +#include "opt_hwpmc_hooks.h" +#include "opt_kdtrace.h" +#include "opt_no_adaptive_rwlocks.h" + +#include <sys/param.h> +#include <sys/ktr.h> +#include <sys/kernel.h> +#include <sys/lock.h> +#include <sys/mutex.h> +#include <sys/proc.h> +#include <sys/rwlock.h> +#include <sys/sysctl.h> +#include <sys/systm.h> +#include <sys/turnstile.h> + +#include <machine/cpu.h> + +#if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS) +#define ADAPTIVE_RWLOCKS +#endif + +#ifdef HWPMC_HOOKS +#include <sys/pmckern.h> +PMC_SOFT_DECLARE( , , lock, failed); +#endif + +/* + * Return the rwlock address when the lock cookie address is provided. + * This functionality assumes that struct rwlock* have a member named rw_lock. + */ +#define rwlock2rw(c) (__containerof(c, struct rwlock, rw_lock)) + +#ifdef ADAPTIVE_RWLOCKS +static int rowner_retries = 10; +static int rowner_loops = 10000; +static 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 <ddb/ddb.h> + +static void db_show_rwlock(const struct lock_object *lock); +#endif +static void assert_rw(const struct lock_object *lock, int what); +static void lock_rw(struct lock_object *lock, int how); +#ifdef KDTRACE_HOOKS +static int owner_rw(const 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(c, what, file, line) +#endif + +void +assert_rw(const struct lock_object *lock, int what) +{ + + rw_assert((const 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(const struct lock_object *lock, struct thread **owner) +{ + const struct rwlock *rw = (const 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(volatile uintptr_t *c, const char *name, int opts) +{ + struct rwlock *rw; + int flags; + + rw = rwlock2rw(c); + + MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET | + RW_RECURSE)) == 0); + ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock, + ("%s: rw_lock not aligned for %s: %p", __func__, name, + &rw->rw_lock)); + + flags = LO_UPGRADABLE; + if (opts & RW_DUPOK) + flags |= LO_DUPOK; + if (opts & RW_NOPROFILE) + flags |= LO_NOPROFILE; + if (!(opts & RW_NOWITNESS)) + flags |= LO_WITNESS; + if (opts & RW_RECURSE) + flags |= LO_RECURSABLE; + if (opts & RW_QUIET) + flags |= LO_QUIET; + + rw->rw_lock = RW_UNLOCKED; + rw->rw_recurse = 0; + lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags); +} + +void +_rw_destroy(volatile uintptr_t *c) +{ + struct rwlock *rw; + + rw = rwlock2rw(c); + + KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw)); + KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw)); + rw->rw_lock = RW_DESTROYED; + lock_destroy(&rw->lock_object); +} + +void +rw_sysinit(void *arg) +{ + struct rw_args *args = arg; + + rw_init((struct rwlock *)args->ra_rw, args->ra_desc); +} + +void +rw_sysinit_flags(void *arg) +{ + struct rw_args_flags *args = arg; + + rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc, + args->ra_flags); +} + +int +_rw_wowned(const volatile uintptr_t *c) +{ + + return (rw_wowner(rwlock2rw(c)) == curthread); +} + +void +_rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line) +{ + struct rwlock *rw; + + if (SCHEDULER_STOPPED()) + return; + + rw = rwlock2rw(c); + + KASSERT(!TD_IS_IDLETHREAD(curthread), + ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d", + curthread, rw->lock_object.lo_name, file, line)); + 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(volatile uintptr_t *c, const char *file, int line) +{ + struct rwlock *rw; + int rval; + + if (SCHEDULER_STOPPED()) + return (1); + + rw = rwlock2rw(c); + + KASSERT(!TD_IS_IDLETHREAD(curthread), + ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d", + curthread, rw->lock_object.lo_name, file, line)); + 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 & LO_RECURSABLE) != 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_cookie(volatile uintptr_t *c, const char *file, int line) +{ + struct rwlock *rw; + + if (SCHEDULER_STOPPED()) + return; + + rw = rwlock2rw(c); + + KASSERT(rw->rw_lock != RW_DESTROYED, + ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line)); + __rw_assert(c, 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(volatile uintptr_t *c, const char *file, int line) +{ + struct rwlock *rw; + 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 + + if (SCHEDULER_STOPPED()) + return; + + rw = rwlock2rw(c); + + KASSERT(!TD_IS_IDLETHREAD(curthread), + ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d", + curthread, rw->lock_object.lo_name, file, line)); + 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; + } + continue; + } +#ifdef HWPMC_HOOKS + PMC_SOFT_CALL( , , lock, failed); +#endif + 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); + continue; + } + +#ifdef ADAPTIVE_RWLOCKS + /* + * 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); + 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); + 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(volatile uintptr_t *c, const char *file, int line) +{ + struct rwlock *rw; + uintptr_t x; + + if (SCHEDULER_STOPPED()) + return (1); + + rw = rwlock2rw(c); + + KASSERT(!TD_IS_IDLETHREAD(curthread), + ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d", + curthread, rw->lock_object.lo_name, file, line)); + + 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_cookie(volatile uintptr_t *c, const char *file, int line) +{ + struct rwlock *rw; + struct turnstile *ts; + uintptr_t x, v, queue; + + if (SCHEDULER_STOPPED()) + return; + + rw = rwlock2rw(c); + + KASSERT(rw->rw_lock != RW_DESTROYED, + ("rw_runlock() of destroyed rwlock @ %s:%d", file, line)); + __rw_assert(c, 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_rel_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_rel_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_rel_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(volatile uintptr_t *c, uintptr_t tid, const char *file, + int line) +{ + struct rwlock *rw; + 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 (SCHEDULER_STOPPED()) + return; + + rw = rwlock2rw(c); + + if (rw_wlocked(rw)) { + KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE, + ("%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 +#ifdef HWPMC_HOOKS + PMC_SOFT_CALL( , , lock, failed); +#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)) { + 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 + /* + * 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); + 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); + 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); + 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(volatile uintptr_t *c, uintptr_t tid, const char *file, + int line) +{ + struct rwlock *rw; + struct turnstile *ts; + uintptr_t v; + int queue; + + if (SCHEDULER_STOPPED()) + return; + + rw = rwlock2rw(c); + + 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(volatile uintptr_t *c, const char *file, int line) +{ + struct rwlock *rw; + uintptr_t v, x, tid; + struct turnstile *ts; + int success; + + if (SCHEDULER_STOPPED()) + return (1); + + rw = rwlock2rw(c); + + KASSERT(rw->rw_lock != RW_DESTROYED, + ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line)); + __rw_assert(c, 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(volatile uintptr_t *c, const char *file, int line) +{ + struct rwlock *rw; + struct turnstile *ts; + uintptr_t tid, v; + int rwait, wwait; + + if (SCHEDULER_STOPPED()) + return; + + rw = rwlock2rw(c); + + KASSERT(rw->rw_lock != RW_DESTROYED, + ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line)); + __rw_assert(c, 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(const volatile uintptr_t *c, int what, const char *file, int line) +{ + const struct rwlock *rw; + + if (panicstr != NULL) + return; + + rw = rwlock2rw(c); + + 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(const struct lock_object *lock) +{ + const struct rwlock *rw; + struct thread *td; + + rw = (const 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 |
