freebsd-dev/module/zfs/zrlock.c

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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2014 by Delphix. All rights reserved.
*/
/*
* A Zero Reference Lock (ZRL) is a reference count that can lock out new
* references only when the count is zero and only without waiting if the count
* is not already zero. It is similar to a read-write lock in that it allows
* multiple readers and only a single writer, but it does not allow a writer to
* block while waiting for readers to exit, and therefore the question of
* reader/writer priority is moot (no WRWANT bit). Since the equivalent of
* rw_enter(&lock, RW_WRITER) is disallowed and only tryenter() is allowed, it
* is perfectly safe for the same reader to acquire the same lock multiple
* times. The fact that a ZRL is reentrant for readers (through multiple calls
* to zrl_add()) makes it convenient for determining whether something is
* actively referenced without the fuss of flagging lock ownership across
* function calls.
*/
#include <sys/zrlock.h>
Remove duplicate typedefs from trace.h Older versions of GCC (e.g. GCC 4.4.7 on RHEL6) do not allow duplicate typedef declarations with the same type. The trace.h header contains some typedefs to avoid 'unknown type' errors for C files that haven't declared the type in question. But this causes build failures for C files that have already declared the type. Newer versions of GCC (e.g. v4.6) allow duplicate typedefs with the same type unless pedantic error checking is in force. To support the older versions we need to remove the duplicate typedefs. Removal of the typedefs means we can't built tracepoints code using those types unless the required headers have been included. To facilitate this, all tracepoint event declarations have been moved out of trace.h into separate headers. Each new header is explicitly included from the C file that uses the events defined therein. The trace.h header is still indirectly included form zfs_context.h and provides the implementation of the dprintf(), dbgmsg(), and SET_ERROR() interfaces. This makes those interfaces readily available throughout the code base. The macros that redefine DTRACE_PROBE* to use Linux tracepoints are also still provided by trace.h, so it is a prerequisite for the other trace_*.h headers. These new Linux implementation-specific headers do introduce a small divergence from upstream ZFS in several core C files, but this should not present a significant maintenance burden. Signed-off-by: Ned Bass <bass6@llnl.gov> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Issue #2953
2014-12-13 02:07:39 +00:00
#include <sys/trace_zrlock.h>
/*
* A ZRL can be locked only while there are zero references, so ZRL_LOCKED is
* treated as zero references.
*/
#define ZRL_LOCKED -1
#define ZRL_DESTROYED -2
void
zrl_init(zrlock_t *zrl)
{
mutex_init(&zrl->zr_mtx, NULL, MUTEX_DEFAULT, NULL);
zrl->zr_refcount = 0;
cv_init(&zrl->zr_cv, NULL, CV_DEFAULT, NULL);
#ifdef ZFS_DEBUG
zrl->zr_owner = NULL;
zrl->zr_caller = NULL;
#endif
}
void
zrl_destroy(zrlock_t *zrl)
{
ASSERT0(zrl->zr_refcount);
mutex_destroy(&zrl->zr_mtx);
zrl->zr_refcount = ZRL_DESTROYED;
cv_destroy(&zrl->zr_cv);
}
void
#ifdef ZFS_DEBUG
zrl_add_debug(zrlock_t *zrl, const char *zc)
#else
zrl_add(zrlock_t *zrl)
#endif
{
uint32_t n = (uint32_t)zrl->zr_refcount;
while (n != ZRL_LOCKED) {
uint32_t cas = atomic_cas_32(
(uint32_t *)&zrl->zr_refcount, n, n + 1);
if (cas == n) {
ASSERT3S((int32_t)n, >=, 0);
#ifdef ZFS_DEBUG
if (zrl->zr_owner == curthread) {
DTRACE_PROBE2(zrlock__reentry,
zrlock_t *, zrl, uint32_t, n);
}
zrl->zr_owner = curthread;
zrl->zr_caller = zc;
#endif
return;
}
n = cas;
}
mutex_enter(&zrl->zr_mtx);
while (zrl->zr_refcount == ZRL_LOCKED) {
cv_wait(&zrl->zr_cv, &zrl->zr_mtx);
}
ASSERT3S(zrl->zr_refcount, >=, 0);
zrl->zr_refcount++;
#ifdef ZFS_DEBUG
zrl->zr_owner = curthread;
zrl->zr_caller = zc;
#endif
mutex_exit(&zrl->zr_mtx);
}
void
zrl_remove(zrlock_t *zrl)
{
uint32_t n;
#ifdef ZFS_DEBUG
if (zrl->zr_owner == curthread) {
zrl->zr_owner = NULL;
zrl->zr_caller = NULL;
}
#endif
n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount);
ASSERT3S((int32_t)n, >=, 0);
}
int
zrl_tryenter(zrlock_t *zrl)
{
uint32_t n = (uint32_t)zrl->zr_refcount;
if (n == 0) {
uint32_t cas = atomic_cas_32(
(uint32_t *)&zrl->zr_refcount, 0, ZRL_LOCKED);
if (cas == 0) {
#ifdef ZFS_DEBUG
ASSERT3P(zrl->zr_owner, ==, NULL);
zrl->zr_owner = curthread;
#endif
return (1);
}
}
ASSERT3S((int32_t)n, >, ZRL_DESTROYED);
return (0);
}
void
zrl_exit(zrlock_t *zrl)
{
ASSERT3S(zrl->zr_refcount, ==, ZRL_LOCKED);
mutex_enter(&zrl->zr_mtx);
#ifdef ZFS_DEBUG
ASSERT3P(zrl->zr_owner, ==, curthread);
zrl->zr_owner = NULL;
membar_producer(); /* make sure the owner store happens first */
#endif
zrl->zr_refcount = 0;
cv_broadcast(&zrl->zr_cv);
mutex_exit(&zrl->zr_mtx);
}
int
zrl_refcount(zrlock_t *zrl)
{
int n;
ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
n = (int)zrl->zr_refcount;
return (n <= 0 ? 0 : n);
}
int
zrl_is_zero(zrlock_t *zrl)
{
ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
return (zrl->zr_refcount <= 0);
}
int
zrl_is_locked(zrlock_t *zrl)
{
ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
return (zrl->zr_refcount == ZRL_LOCKED);
}
#ifdef ZFS_DEBUG
kthread_t *
zrl_owner(zrlock_t *zrl)
{
return (zrl->zr_owner);
}
#endif
#if defined(_KERNEL) && defined(HAVE_SPL)
#ifdef ZFS_DEBUG
EXPORT_SYMBOL(zrl_add_debug);
#else
EXPORT_SYMBOL(zrl_add);
#endif
EXPORT_SYMBOL(zrl_remove);
#endif