Update to onnv_147

[zfs.git] / module / zfs / zrlock.c

diff --git a/module/zfs/zrlock.c b/module/zfs/zrlock.c
new file mode 100644 (file)
index 0000000..ec94b08
--- /dev/null
+++ b/module/zfs/zrlock.c
@@ -0,0 +1,194 @@
+/*
+ * 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.
+ */
+
+/*
+ * 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>
+
+/*
+ * A ZRL can be locked only while there are zero references, so ZRL_LOCKED is
+ * treated as zero references.
+ */
+#define        ZRL_LOCKED      ((uint32_t)-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)
+{
+       ASSERT(zrl->zr_refcount == 0);
+
+       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) {
+                       ASSERT((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);
+       }
+       ASSERT(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;
+
+       n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount);
+       ASSERT((int32_t)n >= 0);
+#ifdef ZFS_DEBUG
+       if (zrl->zr_owner == curthread) {
+               zrl->zr_owner = NULL;
+               zrl->zr_caller = NULL;
+       }
+#endif
+}
+
+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
+                       ASSERT(zrl->zr_owner == NULL);
+                       zrl->zr_owner = curthread;
+#endif
+                       return (1);
+               }
+       }
+
+       ASSERT((int32_t)n > ZRL_DESTROYED);
+
+       return (0);
+}
+
+void
+zrl_exit(zrlock_t *zrl)
+{
+       ASSERT(zrl->zr_refcount == ZRL_LOCKED);
+
+       mutex_enter(&zrl->zr_mtx);
+#ifdef ZFS_DEBUG
+       ASSERT(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)
+{
+       ASSERT(zrl->zr_refcount > ZRL_DESTROYED);
+
+       int n = (int)zrl->zr_refcount;
+       return (n <= 0 ? 0 : n);
+}
+
+int
+zrl_is_zero(zrlock_t *zrl)
+{
+       ASSERT(zrl->zr_refcount > ZRL_DESTROYED);
+
+       return (zrl->zr_refcount <= 0);
+}
+
+int
+zrl_is_locked(zrlock_t *zrl)
+{
+       ASSERT(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