diff options
Diffstat (limited to 'include/linux/rculist_nulls.h')
-rw-r--r-- | include/linux/rculist_nulls.h | 189 |
1 files changed, 189 insertions, 0 deletions
diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h new file mode 100644 index 000000000..d8afdb878 --- /dev/null +++ b/include/linux/rculist_nulls.h @@ -0,0 +1,189 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_RCULIST_NULLS_H +#define _LINUX_RCULIST_NULLS_H + +#ifdef __KERNEL__ + +/* + * RCU-protected list version + */ +#include <linux/list_nulls.h> +#include <linux/rcupdate.h> + +/** + * hlist_nulls_del_init_rcu - deletes entry from hash list with re-initialization + * @n: the element to delete from the hash list. + * + * Note: hlist_nulls_unhashed() on the node return true after this. It is + * useful for RCU based read lockfree traversal if the writer side + * must know if the list entry is still hashed or already unhashed. + * + * In particular, it means that we can not poison the forward pointers + * that may still be used for walking the hash list and we can only + * zero the pprev pointer so list_unhashed() will return true after + * this. + * + * The caller must take whatever precautions are necessary (such as + * holding appropriate locks) to avoid racing with another + * list-mutation primitive, such as hlist_nulls_add_head_rcu() or + * hlist_nulls_del_rcu(), running on this same list. However, it is + * perfectly legal to run concurrently with the _rcu list-traversal + * primitives, such as hlist_nulls_for_each_entry_rcu(). + */ +static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n) +{ + if (!hlist_nulls_unhashed(n)) { + __hlist_nulls_del(n); + WRITE_ONCE(n->pprev, NULL); + } +} + +/** + * hlist_nulls_first_rcu - returns the first element of the hash list. + * @head: the head of the list. + */ +#define hlist_nulls_first_rcu(head) \ + (*((struct hlist_nulls_node __rcu __force **)&(head)->first)) + +/** + * hlist_nulls_next_rcu - returns the element of the list after @node. + * @node: element of the list. + */ +#define hlist_nulls_next_rcu(node) \ + (*((struct hlist_nulls_node __rcu __force **)&(node)->next)) + +/** + * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization + * @n: the element to delete from the hash list. + * + * Note: hlist_nulls_unhashed() on entry does not return true after this, + * the entry is in an undefined state. It is useful for RCU based + * lockfree traversal. + * + * In particular, it means that we can not poison the forward + * pointers that may still be used for walking the hash list. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as hlist_nulls_add_head_rcu() + * or hlist_nulls_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * hlist_nulls_for_each_entry(). + */ +static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n) +{ + __hlist_nulls_del(n); + WRITE_ONCE(n->pprev, LIST_POISON2); +} + +/** + * hlist_nulls_add_head_rcu + * @n: the element to add to the hash list. + * @h: the list to add to. + * + * Description: + * Adds the specified element to the specified hlist_nulls, + * while permitting racing traversals. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as hlist_nulls_add_head_rcu() + * or hlist_nulls_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency + * problems on Alpha CPUs. Regardless of the type of CPU, the + * list-traversal primitive must be guarded by rcu_read_lock(). + */ +static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n, + struct hlist_nulls_head *h) +{ + struct hlist_nulls_node *first = h->first; + + n->next = first; + WRITE_ONCE(n->pprev, &h->first); + rcu_assign_pointer(hlist_nulls_first_rcu(h), n); + if (!is_a_nulls(first)) + WRITE_ONCE(first->pprev, &n->next); +} + +/** + * hlist_nulls_add_tail_rcu + * @n: the element to add to the hash list. + * @h: the list to add to. + * + * Description: + * Adds the specified element to the specified hlist_nulls, + * while permitting racing traversals. + * + * The caller must take whatever precautions are necessary + * (such as holding appropriate locks) to avoid racing + * with another list-mutation primitive, such as hlist_nulls_add_head_rcu() + * or hlist_nulls_del_rcu(), running on this same list. + * However, it is perfectly legal to run concurrently with + * the _rcu list-traversal primitives, such as + * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency + * problems on Alpha CPUs. Regardless of the type of CPU, the + * list-traversal primitive must be guarded by rcu_read_lock(). + */ +static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n, + struct hlist_nulls_head *h) +{ + struct hlist_nulls_node *i, *last = NULL; + + /* Note: write side code, so rcu accessors are not needed. */ + for (i = h->first; !is_a_nulls(i); i = i->next) + last = i; + + if (last) { + n->next = last->next; + n->pprev = &last->next; + rcu_assign_pointer(hlist_next_rcu(last), n); + } else { + hlist_nulls_add_head_rcu(n, h); + } +} + +/* after that hlist_nulls_del will work */ +static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n) +{ + n->pprev = &n->next; + n->next = (struct hlist_nulls_node *)NULLS_MARKER(NULL); +} + +/** + * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type + * @tpos: the type * to use as a loop cursor. + * @pos: the &struct hlist_nulls_node to use as a loop cursor. + * @head: the head of the list. + * @member: the name of the hlist_nulls_node within the struct. + * + * The barrier() is needed to make sure compiler doesn't cache first element [1], + * as this loop can be restarted [2] + * [1] Documentation/memory-barriers.txt around line 1533 + * [2] Documentation/RCU/rculist_nulls.rst around line 146 + */ +#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \ + for (({barrier();}), \ + pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \ + (!is_a_nulls(pos)) && \ + ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \ + pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos))) + +/** + * hlist_nulls_for_each_entry_safe - + * iterate over list of given type safe against removal of list entry + * @tpos: the type * to use as a loop cursor. + * @pos: the &struct hlist_nulls_node to use as a loop cursor. + * @head: the head of the list. + * @member: the name of the hlist_nulls_node within the struct. + */ +#define hlist_nulls_for_each_entry_safe(tpos, pos, head, member) \ + for (({barrier();}), \ + pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \ + (!is_a_nulls(pos)) && \ + ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); \ + pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)); 1; });) +#endif +#endif |