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kern_rangelock.c
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/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* Copyright (c) 2009 Konstantin Belousov <kib@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 unmodified, 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.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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.
*/
#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/rangelock.h>
#include <sys/systm.h>
#include <vm/uma.h>
struct rl_q_entry {
TAILQ_ENTRY(rl_q_entry) rl_q_link;
off_t rl_q_start, rl_q_end;
int rl_q_flags;
};
static uma_zone_t rl_entry_zone;
static void
rangelock_sys_init(void)
{
rl_entry_zone = uma_zcreate("rl_entry", sizeof(struct rl_q_entry),
NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
}
SYSINIT(vfs, SI_SUB_LOCK, SI_ORDER_ANY, rangelock_sys_init, NULL);
static struct rl_q_entry *
rlqentry_alloc(void)
{
return (uma_zalloc(rl_entry_zone, M_WAITOK));
}
void
rlqentry_free(struct rl_q_entry *rleq)
{
uma_zfree(rl_entry_zone, rleq);
}
void
rangelock_init(struct rangelock *lock)
{
TAILQ_INIT(&lock->rl_waiters);
lock->rl_currdep = NULL;
}
void
rangelock_destroy(struct rangelock *lock)
{
KASSERT(TAILQ_EMPTY(&lock->rl_waiters), ("Dangling waiters"));
}
/*
* Two entries are compatible if their ranges do not overlap, or both
* entries are for read.
*/
static int
ranges_overlap(const struct rl_q_entry *e1,
const struct rl_q_entry *e2)
{
if (e1->rl_q_start < e2->rl_q_end && e1->rl_q_end > e2->rl_q_start)
return (1);
return (0);
}
/*
* Recalculate the lock->rl_currdep after an unlock.
*/
static void
rangelock_calc_block(struct rangelock *lock)
{
struct rl_q_entry *entry, *nextentry, *entry1;
for (entry = lock->rl_currdep; entry != NULL; entry = nextentry) {
nextentry = TAILQ_NEXT(entry, rl_q_link);
if (entry->rl_q_flags & RL_LOCK_READ) {
/* Reads must not overlap with granted writes. */
for (entry1 = TAILQ_FIRST(&lock->rl_waiters);
!(entry1->rl_q_flags & RL_LOCK_READ);
entry1 = TAILQ_NEXT(entry1, rl_q_link)) {
if (ranges_overlap(entry, entry1))
goto out;
}
} else {
/* Write must not overlap with any granted locks. */
for (entry1 = TAILQ_FIRST(&lock->rl_waiters);
entry1 != entry;
entry1 = TAILQ_NEXT(entry1, rl_q_link)) {
if (ranges_overlap(entry, entry1))
goto out;
}
/* Move grantable write locks to the front. */
TAILQ_REMOVE(&lock->rl_waiters, entry, rl_q_link);
TAILQ_INSERT_HEAD(&lock->rl_waiters, entry, rl_q_link);
}
/* Grant this lock. */
entry->rl_q_flags |= RL_LOCK_GRANTED;
wakeup(entry);
}
out:
lock->rl_currdep = entry;
}
static void
rangelock_unlock_locked(struct rangelock *lock, struct rl_q_entry *entry,
struct mtx *ilk, bool do_calc_block)
{
MPASS(lock != NULL && entry != NULL && ilk != NULL);
mtx_assert(ilk, MA_OWNED);
if (!do_calc_block) {
/*
* This is the case where rangelock_enqueue() has been called
* with trylock == true and just inserted this entry in the
* queue.
* If rl_currdep is this entry, rl_currdep needs to
* be set to the next entry in the rl_waiters list.
* However, since this entry is the last entry in the
* list, the next entry is NULL.
*/
if (lock->rl_currdep == entry) {
KASSERT(TAILQ_NEXT(lock->rl_currdep, rl_q_link) == NULL,
("rangelock_enqueue: next entry not NULL"));
lock->rl_currdep = NULL;
}
} else
KASSERT(entry != lock->rl_currdep, ("stuck currdep"));
TAILQ_REMOVE(&lock->rl_waiters, entry, rl_q_link);
if (do_calc_block)
rangelock_calc_block(lock);
mtx_unlock(ilk);
if (curthread->td_rlqe == NULL)
curthread->td_rlqe = entry;
else
rlqentry_free(entry);
}
void
rangelock_unlock(struct rangelock *lock, void *cookie, struct mtx *ilk)
{
MPASS(lock != NULL && cookie != NULL && ilk != NULL);
mtx_lock(ilk);
rangelock_unlock_locked(lock, cookie, ilk, true);
}
/*
* Unlock the sub-range of granted lock.
*/
void *
rangelock_unlock_range(struct rangelock *lock, void *cookie, off_t start,
off_t end, struct mtx *ilk)
{
struct rl_q_entry *entry;
MPASS(lock != NULL && cookie != NULL && ilk != NULL);
entry = cookie;
KASSERT(entry->rl_q_flags & RL_LOCK_GRANTED,
("Unlocking non-granted lock"));
KASSERT(entry->rl_q_start == start, ("wrong start"));
KASSERT(entry->rl_q_end >= end, ("wrong end"));
mtx_lock(ilk);
if (entry->rl_q_end == end) {
rangelock_unlock_locked(lock, cookie, ilk, true);
return (NULL);
}
entry->rl_q_end = end;
rangelock_calc_block(lock);
mtx_unlock(ilk);
return (cookie);
}
/*
* Add the lock request to the queue of the pending requests for
* rangelock. Sleep until the request can be granted unless trylock == true.
*/
static void *
rangelock_enqueue(struct rangelock *lock, off_t start, off_t end, int mode,
struct mtx *ilk, bool trylock)
{
struct rl_q_entry *entry;
struct thread *td;
MPASS(lock != NULL && ilk != NULL);
td = curthread;
if (td->td_rlqe != NULL) {
entry = td->td_rlqe;
td->td_rlqe = NULL;
} else
entry = rlqentry_alloc();
MPASS(entry != NULL);
entry->rl_q_flags = mode;
entry->rl_q_start = start;
entry->rl_q_end = end;
mtx_lock(ilk);
/*
* XXXKIB TODO. Check that a thread does not try to enqueue a
* lock that is incompatible with another request from the same
* thread.
*/
TAILQ_INSERT_TAIL(&lock->rl_waiters, entry, rl_q_link);
/*
* If rl_currdep == NULL, there is no entry waiting for a conflicting
* range to be resolved, so set rl_currdep to this entry. If there is
* no conflicting entry for this entry, rl_currdep will be set back to
* NULL by rangelock_calc_block().
*/
if (lock->rl_currdep == NULL)
lock->rl_currdep = entry;
rangelock_calc_block(lock);
while (!(entry->rl_q_flags & RL_LOCK_GRANTED)) {
if (trylock) {
/*
* For this case, the range is not actually locked
* yet, but removal from the list requires the same
* steps, except for not doing a rangelock_calc_block()
* call, since rangelock_calc_block() was called above.
*/
rangelock_unlock_locked(lock, entry, ilk, false);
return (NULL);
}
msleep(entry, ilk, 0, "range", 0);
}
mtx_unlock(ilk);
return (entry);
}
void *
rangelock_rlock(struct rangelock *lock, off_t start, off_t end, struct mtx *ilk)
{
return (rangelock_enqueue(lock, start, end, RL_LOCK_READ, ilk, false));
}
void *
rangelock_tryrlock(struct rangelock *lock, off_t start, off_t end,
struct mtx *ilk)
{
return (rangelock_enqueue(lock, start, end, RL_LOCK_READ, ilk, true));
}
void *
rangelock_wlock(struct rangelock *lock, off_t start, off_t end, struct mtx *ilk)
{
return (rangelock_enqueue(lock, start, end, RL_LOCK_WRITE, ilk, false));
}
void *
rangelock_trywlock(struct rangelock *lock, off_t start, off_t end,
struct mtx *ilk)
{
return (rangelock_enqueue(lock, start, end, RL_LOCK_WRITE, ilk, true));
}
#ifdef INVARIANT_SUPPORT
void
_rangelock_cookie_assert(void *cookie, int what, const char *file, int line)
{
struct rl_q_entry *entry;
int flags;
MPASS(cookie != NULL);
entry = cookie;
flags = entry->rl_q_flags;
switch (what) {
case RCA_LOCKED:
if ((flags & RL_LOCK_GRANTED) == 0)
panic("rangelock not held @ %s:%d\n", file, line);
break;
case RCA_RLOCKED:
if ((flags & (RL_LOCK_GRANTED | RL_LOCK_READ)) !=
(RL_LOCK_GRANTED | RL_LOCK_READ))
panic("rangelock not rlocked @ %s:%d\n", file, line);
break;
case RCA_WLOCKED:
if ((flags & (RL_LOCK_GRANTED | RL_LOCK_WRITE)) !=
(RL_LOCK_GRANTED | RL_LOCK_WRITE))
panic("rangelock not wlocked @ %s:%d\n", file, line);
break;
default:
panic("Unknown rangelock assertion: %d @ %s:%d", what, file,
line);
}
}
#endif /* INVARIANT_SUPPORT */

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