refcount.c

/*
 * 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 https://opensource.org/licenses/CDDL-1.0.
 * 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) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012, 2021 by Delphix. All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/zfs_refcount.h>

#ifdef	ZFS_DEBUG
/*
 * Reference count tracking is disabled by default.  It's memory requirements
 * are reasonable, however as implemented it consumes a significant amount of
 * cpu time.  Until its performance is improved it should be manually enabled.
 */
int reference_tracking_enable = B_FALSE;
static uint_t reference_history = 3; /* tunable */

static kmem_cache_t *reference_cache;

void
zfs_refcount_init(void)
{
	reference_cache = kmem_cache_create("reference_cache",
	    sizeof (reference_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
}

void
zfs_refcount_fini(void)
{
	kmem_cache_destroy(reference_cache);
}

static int
zfs_refcount_compare(const void *x1, const void *x2)
{
	const reference_t *r1 = (const reference_t *)x1;
	const reference_t *r2 = (const reference_t *)x2;

	int cmp1 = TREE_CMP(r1->ref_holder, r2->ref_holder);
	int cmp2 = TREE_CMP(r1->ref_number, r2->ref_number);
	int cmp = cmp1 ? cmp1 : cmp2;
	return ((cmp || r1->ref_search) ? cmp : TREE_PCMP(r1, r2));
}

void
zfs_refcount_create(zfs_refcount_t *rc)
{
	mutex_init(&rc->rc_mtx, NULL, MUTEX_DEFAULT, NULL);
	avl_create(&rc->rc_tree, zfs_refcount_compare, sizeof (reference_t),
	    offsetof(reference_t, ref_link.a));
	list_create(&rc->rc_removed, sizeof (reference_t),
	    offsetof(reference_t, ref_link.l));
	rc->rc_count = 0;
	rc->rc_removed_count = 0;
	rc->rc_tracked = reference_tracking_enable;
}

void
zfs_refcount_create_tracked(zfs_refcount_t *rc)
{
	zfs_refcount_create(rc);
	rc->rc_tracked = B_TRUE;
}

void
zfs_refcount_create_untracked(zfs_refcount_t *rc)
{
	zfs_refcount_create(rc);
	rc->rc_tracked = B_FALSE;
}

void
zfs_refcount_destroy_many(zfs_refcount_t *rc, uint64_t number)
{
	reference_t *ref;
	void *cookie = NULL;

	ASSERT3U(rc->rc_count, ==, number);
	while ((ref = avl_destroy_nodes(&rc->rc_tree, &cookie)) != NULL)
		kmem_cache_free(reference_cache, ref);
	avl_destroy(&rc->rc_tree);

	while ((ref = list_remove_head(&rc->rc_removed)))
		kmem_cache_free(reference_cache, ref);
	list_destroy(&rc->rc_removed);
	mutex_destroy(&rc->rc_mtx);
}

void
zfs_refcount_destroy(zfs_refcount_t *rc)
{
	zfs_refcount_destroy_many(rc, 0);
}

int
zfs_refcount_is_zero(zfs_refcount_t *rc)
{
	return (zfs_refcount_count(rc) == 0);
}

int64_t
zfs_refcount_count(zfs_refcount_t *rc)
{
	return (atomic_load_64(&rc->rc_count));
}

int64_t
zfs_refcount_add_many(zfs_refcount_t *rc, uint64_t number, const void *holder)
{
	reference_t *ref;
	int64_t count;

	if (likely(!rc->rc_tracked)) {
		count = atomic_add_64_nv(&(rc)->rc_count, number);
		ASSERT3U(count, >=, number);
		return (count);
	}

	ref = kmem_cache_alloc(reference_cache, KM_SLEEP);
	ref->ref_holder = holder;
	ref->ref_number = number;
	ref->ref_search = B_FALSE;
	mutex_enter(&rc->rc_mtx);
	avl_add(&rc->rc_tree, ref);
	rc->rc_count += number;
	count = rc->rc_count;
	mutex_exit(&rc->rc_mtx);

	return (count);
}

int64_t
zfs_refcount_add(zfs_refcount_t *rc, const void *holder)
{
	return (zfs_refcount_add_many(rc, 1, holder));
}

void
zfs_refcount_add_few(zfs_refcount_t *rc, uint64_t number, const void *holder)
{
	if (likely(!rc->rc_tracked))
		(void) zfs_refcount_add_many(rc, number, holder);
	else for (; number > 0; number--)
		(void) zfs_refcount_add(rc, holder);
}

int64_t
zfs_refcount_remove_many(zfs_refcount_t *rc, uint64_t number,
    const void *holder)
{
	reference_t *ref, s;
	int64_t count;

	if (likely(!rc->rc_tracked)) {
		count = atomic_add_64_nv(&(rc)->rc_count, -number);
		ASSERT3S(count, >=, 0);
		return (count);
	}

	s.ref_holder = holder;
	s.ref_number = number;
	s.ref_search = B_TRUE;
	mutex_enter(&rc->rc_mtx);
	ASSERT3U(rc->rc_count, >=, number);
	ref = avl_find(&rc->rc_tree, &s, NULL);
	if (unlikely(ref == NULL)) {
		panic("No such hold %p on refcount %llx", holder,
		    (u_longlong_t)(uintptr_t)rc);
		return (-1);
	}
	avl_remove(&rc->rc_tree, ref);
	if (reference_history > 0) {
		list_insert_head(&rc->rc_removed, ref);
		if (rc->rc_removed_count >= reference_history) {
			ref = list_remove_tail(&rc->rc_removed);
			kmem_cache_free(reference_cache, ref);
		} else {
			rc->rc_removed_count++;
		}
	} else {
		kmem_cache_free(reference_cache, ref);
	}
	rc->rc_count -= number;
	count = rc->rc_count;
	mutex_exit(&rc->rc_mtx);
	return (count);
}

int64_t
zfs_refcount_remove(zfs_refcount_t *rc, const void *holder)
{
	return (zfs_refcount_remove_many(rc, 1, holder));
}

void
zfs_refcount_remove_few(zfs_refcount_t *rc, uint64_t number, const void *holder)
{
	if (likely(!rc->rc_tracked))
		(void) zfs_refcount_remove_many(rc, number, holder);
	else for (; number > 0; number--)
		(void) zfs_refcount_remove(rc, holder);
}

void
zfs_refcount_transfer(zfs_refcount_t *dst, zfs_refcount_t *src)
{
	avl_tree_t tree;
	list_t removed;
	reference_t *ref;
	void *cookie = NULL;
	uint64_t count;
	uint_t removed_count;

	avl_create(&tree, zfs_refcount_compare, sizeof (reference_t),
	    offsetof(reference_t, ref_link.a));
	list_create(&removed, sizeof (reference_t),
	    offsetof(reference_t, ref_link.l));

	mutex_enter(&src->rc_mtx);
	count = src->rc_count;
	removed_count = src->rc_removed_count;
	src->rc_count = 0;
	src->rc_removed_count = 0;
	avl_swap(&tree, &src->rc_tree);
	list_move_tail(&removed, &src->rc_removed);
	mutex_exit(&src->rc_mtx);

	mutex_enter(&dst->rc_mtx);
	dst->rc_count += count;
	dst->rc_removed_count += removed_count;
	if (avl_is_empty(&dst->rc_tree))
		avl_swap(&dst->rc_tree, &tree);
	else while ((ref = avl_destroy_nodes(&tree, &cookie)) != NULL)
		avl_add(&dst->rc_tree, ref);
	list_move_tail(&dst->rc_removed, &removed);
	mutex_exit(&dst->rc_mtx);

	avl_destroy(&tree);
	list_destroy(&removed);
}

void
zfs_refcount_transfer_ownership_many(zfs_refcount_t *rc, uint64_t number,
    const void *current_holder, const void *new_holder)
{
	reference_t *ref, s;

	if (likely(!rc->rc_tracked))
		return;

	s.ref_holder = current_holder;
	s.ref_number = number;
	s.ref_search = B_TRUE;
	mutex_enter(&rc->rc_mtx);
	ref = avl_find(&rc->rc_tree, &s, NULL);
	ASSERT(ref);
	ref->ref_holder = new_holder;
	avl_update(&rc->rc_tree, ref);
	mutex_exit(&rc->rc_mtx);
}

void
zfs_refcount_transfer_ownership(zfs_refcount_t *rc, const void *current_holder,
    const void *new_holder)
{
	return (zfs_refcount_transfer_ownership_many(rc, 1, current_holder,
	    new_holder));
}

/*
 * If tracking is enabled, return true if a reference exists that matches
 * the "holder" tag. If tracking is disabled, then return true if a reference
 * might be held.
 */
boolean_t
zfs_refcount_held(zfs_refcount_t *rc, const void *holder)
{
	reference_t *ref, s;
	avl_index_t idx;
	boolean_t res;

	if (likely(!rc->rc_tracked))
		return (zfs_refcount_count(rc) > 0);

	s.ref_holder = holder;
	s.ref_number = 0;
	s.ref_search = B_TRUE;
	mutex_enter(&rc->rc_mtx);
	ref = avl_find(&rc->rc_tree, &s, &idx);
	if (likely(ref == NULL))
		ref = avl_nearest(&rc->rc_tree, idx, AVL_AFTER);
	res = ref && ref->ref_holder == holder;
	mutex_exit(&rc->rc_mtx);
	return (res);
}

/*
 * If tracking is enabled, return true if a reference does not exist that
 * matches the "holder" tag. If tracking is disabled, always return true
 * since the reference might not be held.
 */
boolean_t
zfs_refcount_not_held(zfs_refcount_t *rc, const void *holder)
{
	reference_t *ref, s;
	avl_index_t idx;
	boolean_t res;

	if (likely(!rc->rc_tracked))
		return (B_TRUE);

	mutex_enter(&rc->rc_mtx);
	s.ref_holder = holder;
	s.ref_number = 0;
	s.ref_search = B_TRUE;
	ref = avl_find(&rc->rc_tree, &s, &idx);
	if (likely(ref == NULL))
		ref = avl_nearest(&rc->rc_tree, idx, AVL_AFTER);
	res = ref == NULL || ref->ref_holder != holder;
	mutex_exit(&rc->rc_mtx);
	return (res);
}

EXPORT_SYMBOL(zfs_refcount_create);
EXPORT_SYMBOL(zfs_refcount_destroy);
EXPORT_SYMBOL(zfs_refcount_is_zero);
EXPORT_SYMBOL(zfs_refcount_count);
EXPORT_SYMBOL(zfs_refcount_add);
EXPORT_SYMBOL(zfs_refcount_remove);
EXPORT_SYMBOL(zfs_refcount_held);

/* BEGIN CSTYLED */
ZFS_MODULE_PARAM(zfs, , reference_tracking_enable, INT, ZMOD_RW,
	"Track reference holders to refcount_t objects");

ZFS_MODULE_PARAM(zfs, , reference_history, UINT, ZMOD_RW,
	"Maximum reference holders being tracked");
/* END CSTYLED */
#endif	/* ZFS_DEBUG */