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353998acc3
a pointer-fetching specific operation check. Consequently, rename the operation ASSERT_ATOMIC_LOAD_PTR(). * Fix the implementation of ASSERT_ATOMIC_LOAD_PTR() by checking directly alignment on the word boundry, for all the given specific architectures. That's a bit too strict for some common case, but it assures safety. * Add a comment explaining the scope of the macro * Add a new stub in the lockmgr specific implementation Tested by: marcel (initial version), marius Reviewed by: rwatson, jhb (comment specific review) Approved by: re (kib)
1126 lines
30 KiB
C
1126 lines
30 KiB
C
/*-
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* Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the author nor the names of any co-contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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/*
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* Machine independent bits of reader/writer lock implementation.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "opt_ddb.h"
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#include "opt_kdtrace.h"
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#include "opt_no_adaptive_rwlocks.h"
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#include <sys/param.h>
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#include <sys/ktr.h>
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#include <sys/kernel.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/proc.h>
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#include <sys/rwlock.h>
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#include <sys/sysctl.h>
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#include <sys/systm.h>
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#include <sys/turnstile.h>
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#include <machine/cpu.h>
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#if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS)
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#define ADAPTIVE_RWLOCKS
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#endif
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#ifdef ADAPTIVE_RWLOCKS
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static int rowner_retries = 10;
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static int rowner_loops = 10000;
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SYSCTL_NODE(_debug, OID_AUTO, rwlock, CTLFLAG_RD, NULL, "rwlock debugging");
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SYSCTL_INT(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, "");
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SYSCTL_INT(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, "");
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#endif
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#ifdef DDB
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#include <ddb/ddb.h>
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static void db_show_rwlock(struct lock_object *lock);
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#endif
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static void assert_rw(struct lock_object *lock, int what);
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static void lock_rw(struct lock_object *lock, int how);
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#ifdef KDTRACE_HOOKS
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static int owner_rw(struct lock_object *lock, struct thread **owner);
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#endif
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static int unlock_rw(struct lock_object *lock);
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struct lock_class lock_class_rw = {
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.lc_name = "rw",
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.lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE,
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.lc_assert = assert_rw,
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#ifdef DDB
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.lc_ddb_show = db_show_rwlock,
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#endif
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.lc_lock = lock_rw,
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.lc_unlock = unlock_rw,
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#ifdef KDTRACE_HOOKS
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.lc_owner = owner_rw,
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#endif
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};
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/*
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* Return a pointer to the owning thread if the lock is write-locked or
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* NULL if the lock is unlocked or read-locked.
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*/
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#define rw_wowner(rw) \
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((rw)->rw_lock & RW_LOCK_READ ? NULL : \
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(struct thread *)RW_OWNER((rw)->rw_lock))
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/*
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* Returns if a write owner is recursed. Write ownership is not assured
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* here and should be previously checked.
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*/
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#define rw_recursed(rw) ((rw)->rw_recurse != 0)
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/*
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* Return true if curthread helds the lock.
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*/
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#define rw_wlocked(rw) (rw_wowner((rw)) == curthread)
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/*
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* Return a pointer to the owning thread for this lock who should receive
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* any priority lent by threads that block on this lock. Currently this
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* is identical to rw_wowner().
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*/
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#define rw_owner(rw) rw_wowner(rw)
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#ifndef INVARIANTS
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#define _rw_assert(rw, what, file, line)
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#endif
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void
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assert_rw(struct lock_object *lock, int what)
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{
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rw_assert((struct rwlock *)lock, what);
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}
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void
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lock_rw(struct lock_object *lock, int how)
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{
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struct rwlock *rw;
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rw = (struct rwlock *)lock;
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if (how)
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rw_wlock(rw);
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else
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rw_rlock(rw);
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}
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int
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unlock_rw(struct lock_object *lock)
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{
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struct rwlock *rw;
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rw = (struct rwlock *)lock;
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rw_assert(rw, RA_LOCKED | LA_NOTRECURSED);
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if (rw->rw_lock & RW_LOCK_READ) {
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rw_runlock(rw);
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return (0);
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} else {
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rw_wunlock(rw);
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return (1);
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}
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}
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#ifdef KDTRACE_HOOKS
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int
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owner_rw(struct lock_object *lock, struct thread **owner)
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{
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struct rwlock *rw = (struct rwlock *)lock;
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uintptr_t x = rw->rw_lock;
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*owner = rw_wowner(rw);
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return ((x & RW_LOCK_READ) != 0 ? (RW_READERS(x) != 0) :
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(*owner != NULL));
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}
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#endif
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void
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rw_init_flags(struct rwlock *rw, const char *name, int opts)
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{
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int flags;
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MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET |
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RW_RECURSE)) == 0);
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ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock,
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("%s: rw_lock not aligned for %s: %p", __func__, name,
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&rw->rw_lock));
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flags = LO_UPGRADABLE;
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if (opts & RW_DUPOK)
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flags |= LO_DUPOK;
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if (opts & RW_NOPROFILE)
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flags |= LO_NOPROFILE;
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if (!(opts & RW_NOWITNESS))
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flags |= LO_WITNESS;
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if (opts & RW_RECURSE)
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flags |= LO_RECURSABLE;
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if (opts & RW_QUIET)
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flags |= LO_QUIET;
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rw->rw_lock = RW_UNLOCKED;
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rw->rw_recurse = 0;
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lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags);
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}
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void
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rw_destroy(struct rwlock *rw)
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{
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KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock not unlocked"));
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KASSERT(rw->rw_recurse == 0, ("rw lock still recursed"));
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rw->rw_lock = RW_DESTROYED;
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lock_destroy(&rw->lock_object);
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}
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void
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rw_sysinit(void *arg)
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{
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struct rw_args *args = arg;
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rw_init(args->ra_rw, args->ra_desc);
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}
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void
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rw_sysinit_flags(void *arg)
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{
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struct rw_args_flags *args = arg;
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rw_init_flags(args->ra_rw, args->ra_desc, args->ra_flags);
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}
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int
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rw_wowned(struct rwlock *rw)
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{
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return (rw_wowner(rw) == curthread);
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}
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void
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_rw_wlock(struct rwlock *rw, const char *file, int line)
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{
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MPASS(curthread != NULL);
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KASSERT(rw->rw_lock != RW_DESTROYED,
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("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
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WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
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line, NULL);
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__rw_wlock(rw, curthread, file, line);
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LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line);
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WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
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curthread->td_locks++;
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}
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int
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_rw_try_wlock(struct rwlock *rw, const char *file, int line)
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{
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int rval;
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KASSERT(rw->rw_lock != RW_DESTROYED,
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("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
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if (rw_wlocked(rw) &&
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(rw->lock_object.lo_flags & LO_RECURSABLE) != 0) {
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rw->rw_recurse++;
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rval = 1;
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} else
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rval = atomic_cmpset_acq_ptr(&rw->rw_lock, RW_UNLOCKED,
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(uintptr_t)curthread);
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LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);
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if (rval) {
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WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
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file, line);
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curthread->td_locks++;
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}
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return (rval);
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}
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void
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_rw_wunlock(struct rwlock *rw, const char *file, int line)
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{
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MPASS(curthread != NULL);
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KASSERT(rw->rw_lock != RW_DESTROYED,
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("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
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_rw_assert(rw, RA_WLOCKED, file, line);
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curthread->td_locks--;
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WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
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LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
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line);
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if (!rw_recursed(rw))
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LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_WUNLOCK_RELEASE, rw);
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__rw_wunlock(rw, curthread, file, line);
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}
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/*
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* Determines whether a new reader can acquire a lock. Succeeds if the
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* reader already owns a read lock and the lock is locked for read to
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* prevent deadlock from reader recursion. Also succeeds if the lock
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* is unlocked and has no writer waiters or spinners. Failing otherwise
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* prioritizes writers before readers.
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*/
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#define RW_CAN_READ(_rw) \
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((curthread->td_rw_rlocks && (_rw) & RW_LOCK_READ) || ((_rw) & \
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(RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) == \
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RW_LOCK_READ)
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void
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_rw_rlock(struct rwlock *rw, const char *file, int line)
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{
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struct turnstile *ts;
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#ifdef ADAPTIVE_RWLOCKS
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volatile struct thread *owner;
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int spintries = 0;
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int i;
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#endif
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#ifdef LOCK_PROFILING
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uint64_t waittime = 0;
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int contested = 0;
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#endif
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uintptr_t v;
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#ifdef KDTRACE_HOOKS
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uint64_t spin_cnt = 0;
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uint64_t sleep_cnt = 0;
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int64_t sleep_time = 0;
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#endif
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KASSERT(rw->rw_lock != RW_DESTROYED,
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("rw_rlock() of destroyed rwlock @ %s:%d", file, line));
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KASSERT(rw_wowner(rw) != curthread,
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("%s (%s): wlock already held @ %s:%d", __func__,
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rw->lock_object.lo_name, file, line));
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WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL);
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for (;;) {
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#ifdef KDTRACE_HOOKS
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spin_cnt++;
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#endif
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/*
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* Handle the easy case. If no other thread has a write
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* lock, then try to bump up the count of read locks. Note
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* that we have to preserve the current state of the
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* RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a
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* read lock, then rw_lock must have changed, so restart
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* the loop. Note that this handles the case of a
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* completely unlocked rwlock since such a lock is encoded
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* as a read lock with no waiters.
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*/
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v = rw->rw_lock;
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if (RW_CAN_READ(v)) {
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/*
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* The RW_LOCK_READ_WAITERS flag should only be set
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* if the lock has been unlocked and write waiters
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* were present.
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*/
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if (atomic_cmpset_acq_ptr(&rw->rw_lock, v,
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v + RW_ONE_READER)) {
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if (LOCK_LOG_TEST(&rw->lock_object, 0))
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CTR4(KTR_LOCK,
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"%s: %p succeed %p -> %p", __func__,
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rw, (void *)v,
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(void *)(v + RW_ONE_READER));
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break;
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}
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continue;
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}
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lock_profile_obtain_lock_failed(&rw->lock_object,
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&contested, &waittime);
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#ifdef ADAPTIVE_RWLOCKS
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/*
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* If the owner is running on another CPU, spin until
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* the owner stops running or the state of the lock
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* changes.
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*/
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if ((v & RW_LOCK_READ) == 0) {
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owner = (struct thread *)RW_OWNER(v);
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if (TD_IS_RUNNING(owner)) {
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if (LOCK_LOG_TEST(&rw->lock_object, 0))
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CTR3(KTR_LOCK,
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"%s: spinning on %p held by %p",
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__func__, rw, owner);
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while ((struct thread*)RW_OWNER(rw->rw_lock) ==
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owner && TD_IS_RUNNING(owner)) {
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cpu_spinwait();
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#ifdef KDTRACE_HOOKS
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spin_cnt++;
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#endif
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}
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continue;
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}
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} else if (spintries < rowner_retries) {
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spintries++;
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for (i = 0; i < rowner_loops; i++) {
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v = rw->rw_lock;
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if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(v))
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break;
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cpu_spinwait();
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}
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if (i != rowner_loops)
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continue;
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}
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#endif
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/*
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* Okay, now it's the hard case. Some other thread already
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* has a write lock or there are write waiters present,
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* acquire the turnstile lock so we can begin the process
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* of blocking.
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*/
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ts = turnstile_trywait(&rw->lock_object);
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/*
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* The lock might have been released while we spun, so
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* recheck its state and restart the loop if needed.
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*/
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v = rw->rw_lock;
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if (RW_CAN_READ(v)) {
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turnstile_cancel(ts);
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continue;
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}
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#ifdef ADAPTIVE_RWLOCKS
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/*
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* The current lock owner might have started executing
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* on another CPU (or the lock could have changed
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* owners) while we were waiting on the turnstile
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* chain lock. If so, drop the turnstile lock and try
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* again.
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*/
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if ((v & RW_LOCK_READ) == 0) {
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owner = (struct thread *)RW_OWNER(v);
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if (TD_IS_RUNNING(owner)) {
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turnstile_cancel(ts);
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continue;
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}
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}
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#endif
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/*
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* The lock is held in write mode or it already has waiters.
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*/
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MPASS(!RW_CAN_READ(v));
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|
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/*
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* If the RW_LOCK_READ_WAITERS flag is already set, then
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* we can go ahead and block. If it is not set then try
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* to set it. If we fail to set it drop the turnstile
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* lock and restart the loop.
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*/
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if (!(v & RW_LOCK_READ_WAITERS)) {
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if (!atomic_cmpset_ptr(&rw->rw_lock, v,
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v | RW_LOCK_READ_WAITERS)) {
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turnstile_cancel(ts);
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continue;
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}
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if (LOCK_LOG_TEST(&rw->lock_object, 0))
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CTR2(KTR_LOCK, "%s: %p set read waiters flag",
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__func__, rw);
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}
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|
|
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/*
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* We were unable to acquire the lock and the read waiters
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* flag is set, so we must block on the turnstile.
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|
*/
|
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if (LOCK_LOG_TEST(&rw->lock_object, 0))
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CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
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rw);
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|
#ifdef KDTRACE_HOOKS
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|
sleep_time -= lockstat_nsecs();
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#endif
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turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE);
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|
#ifdef KDTRACE_HOOKS
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sleep_time += lockstat_nsecs();
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sleep_cnt++;
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#endif
|
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if (LOCK_LOG_TEST(&rw->lock_object, 0))
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CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
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__func__, rw);
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}
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|
|
/*
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|
* TODO: acquire "owner of record" here. Here be turnstile dragons
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|
* however. turnstiles don't like owners changing between calls to
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* turnstile_wait() currently.
|
|
*/
|
|
LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_RLOCK_ACQUIRE, rw, contested,
|
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waittime, file, line);
|
|
LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
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|
WITNESS_LOCK(&rw->lock_object, 0, file, line);
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|
curthread->td_locks++;
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|
curthread->td_rw_rlocks++;
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|
#ifdef KDTRACE_HOOKS
|
|
if (sleep_time)
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|
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 & 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
|
|
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(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
|