[ltt-dev] [PATCH 03/11] Move replace code out from _cds_lfht_add()
Lai Jiangshan
laijs at cn.fujitsu.com
Thu Oct 27 01:29:02 EDT 2011
Hi, Mathieu,
Does any path need to be resent/respinned in previous round?
Don't forgot the two patches followed by this round.
Thank,
Lai
On 10/27/2011 12:31 PM, Mathieu Desnoyers wrote:
> I merged a significantly re-worked version of this patch. Thanks for
> pointing out that the replacement could re-use the uniquify code path!
>
> Mathieu
>
> commit 83beee94416bdffdec505bc33cfd79859f6aa243
> Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> Date: Thu Oct 27 06:30:49 2011 +0200
>
> Move replace code out from _cds_lfht_add()
>
> Original patch from Lai Jiangshan, reworked significantly to keep the
> iterator semantic, where a "next" node is never re-read after being
> looked up within a RCU read-side critical section after it has been
> validated.
>
> Although strictly speaking the "replace" code re-checks that the next
> node is not logically removed with a cmpxchg, I prefer to ensure that
> all lookup paths behave similarly. It will make it easier to track
> behavior later on if they all follow the same rules.
>
> Reported-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
>
> diff --git a/rculfhash.c b/rculfhash.c
> index be995df..b9c184f 100644
> --- a/rculfhash.c
> +++ b/rculfhash.c
> @@ -262,17 +262,12 @@ struct partition_resize_work {
> unsigned long start, unsigned long len);
> };
>
> -enum add_mode {
> - ADD_DEFAULT = 0,
> - ADD_UNIQUE = 1,
> - ADD_REPLACE = 2,
> -};
> -
> static
> -struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
> - unsigned long size,
> - struct cds_lfht_node *node,
> - enum add_mode mode, int dummy);
> +void _cds_lfht_add(struct cds_lfht *ht,
> + unsigned long size,
> + struct cds_lfht_node *node,
> + struct cds_lfht_iter *unique_ret,
> + int dummy);
>
> /*
> * Algorithm to reverse bits in a word by lookup table, extended to
> @@ -855,11 +850,16 @@ end:
> }
> }
>
> +/*
> + * A non-NULL unique_ret pointer uses the "add unique" (or uniquify) add
> + * mode. A NULL unique_ret allows creation of duplicate keys.
> + */
> static
> -struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
> - unsigned long size,
> - struct cds_lfht_node *node,
> - enum add_mode mode, int dummy)
> +void _cds_lfht_add(struct cds_lfht *ht,
> + unsigned long size,
> + struct cds_lfht_node *node,
> + struct cds_lfht_iter *unique_ret,
> + int dummy)
> {
> struct cds_lfht_node *iter_prev, *iter, *next, *new_node, *new_next,
> *return_node;
> @@ -869,8 +869,9 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
> assert(!is_removed(node));
> if (!size) {
> assert(dummy);
> + assert(!unique_ret);
> node->p.next = flag_dummy(get_end());
> - return node; /* Initial first add (head) */
> + return; /* Initial first add (head) */
> }
> lookup = lookup_bucket(ht, size, bit_reverse_ulong(node->p.reverse_hash));
> for (;;) {
> @@ -895,16 +896,15 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
> next = rcu_dereference(clear_flag(iter)->p.next);
> if (unlikely(is_removed(next)))
> goto gc_node;
> - if ((mode == ADD_UNIQUE || mode == ADD_REPLACE)
> + if (unique_ret
> && !is_dummy(next)
> && clear_flag(iter)->p.reverse_hash == node->p.reverse_hash
> && !ht->compare_fct(node->key, node->key_len,
> clear_flag(iter)->key,
> clear_flag(iter)->key_len)) {
> - if (mode == ADD_UNIQUE)
> - return clear_flag(iter);
> - else /* mode == ADD_REPLACE */
> - goto replace;
> + unique_ret->node = clear_flag(iter);
> + unique_ret->next = next;
> + return;
> }
> /* Only account for identical reverse hash once */
> if (iter_prev->p.reverse_hash != clear_flag(iter)->p.reverse_hash
> @@ -931,23 +931,10 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
> new_node) != iter) {
> continue; /* retry */
> } else {
> - if (mode == ADD_REPLACE)
> - return_node = NULL;
> - else /* ADD_DEFAULT and ADD_UNIQUE */
> - return_node = node;
> + return_node = node;
> goto end;
> }
>
> - replace:
> -
> - if (!_cds_lfht_replace(ht, size, clear_flag(iter), next,
> - node)) {
> - return_node = clear_flag(iter);
> - goto end; /* gc already done */
> - } else {
> - continue; /* retry */
> - }
> -
> gc_node:
> assert(!is_removed(iter));
> if (is_dummy(iter))
> @@ -958,7 +945,10 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
> /* retry */
> }
> end:
> - return return_node;
> + if (unique_ret) {
> + unique_ret->node = return_node;
> + /* unique_ret->next left unset, never used. */
> + }
> }
>
> static
> @@ -1094,8 +1084,8 @@ void init_table_populate_partition(struct cds_lfht *ht, unsigned long i,
> i, j, !i ? 0 : (1UL << (i - 1)) + j);
> new_node->p.reverse_hash =
> bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j);
> - (void) _cds_lfht_add(ht, !i ? 0 : (1UL << (i - 1)),
> - new_node, ADD_DEFAULT, 1);
> + _cds_lfht_add(ht, !i ? 0 : (1UL << (i - 1)),
> + new_node, NULL, 1);
> }
> ht->cds_lfht_rcu_read_unlock();
> }
> @@ -1437,7 +1427,7 @@ void cds_lfht_add(struct cds_lfht *ht, struct cds_lfht_node *node)
> node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
>
> size = rcu_dereference(ht->t.size);
> - (void) _cds_lfht_add(ht, size, node, ADD_DEFAULT, 0);
> + _cds_lfht_add(ht, size, node, NULL, 0);
> ht_count_add(ht, size);
> }
>
> @@ -1445,32 +1435,38 @@ struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht,
> struct cds_lfht_node *node)
> {
> unsigned long hash, size;
> - struct cds_lfht_node *ret;
> + struct cds_lfht_iter iter;
>
> hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
> node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
>
> size = rcu_dereference(ht->t.size);
> - ret = _cds_lfht_add(ht, size, node, ADD_UNIQUE, 0);
> - if (ret == node)
> + _cds_lfht_add(ht, size, node, &iter, 0);
> + if (iter.node == node)
> ht_count_add(ht, size);
> - return ret;
> + return iter.node;
> }
>
> struct cds_lfht_node *cds_lfht_add_replace(struct cds_lfht *ht,
> struct cds_lfht_node *node)
> {
> unsigned long hash, size;
> - struct cds_lfht_node *ret;
> + struct cds_lfht_iter iter;
>
> hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
> node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
>
> size = rcu_dereference(ht->t.size);
> - ret = _cds_lfht_add(ht, size, node, ADD_REPLACE, 0);
> - if (ret == NULL)
> - ht_count_add(ht, size);
> - return ret;
> + for (;;) {
> + _cds_lfht_add(ht, size, node, &iter, 0);
> + if (iter.node == node) {
> + ht_count_add(ht, size);
> + return NULL;
> + }
> +
> + if (!_cds_lfht_replace(ht, size, iter.node, iter.next, node))
> + return iter.node;
> + }
> }
>
> int cds_lfht_replace(struct cds_lfht *ht, struct cds_lfht_iter *old_iter,
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