6.12-stable review patch. If anyone has any objections, please let me know.
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From: Xuanqiang Luo luoxuanqiang@kylinos.cn
[ Upstream commit 9c4609225ec1cb551006d6a03c7c4ad8cb5584c0 ]
Add two functions to atomically replace RCU-protected hlist_nulls entries.
Keep using WRITE_ONCE() to assign values to ->next and ->pprev, as mentioned in the patch below: commit efd04f8a8b45 ("rcu: Use WRITE_ONCE() for assignments to ->next for rculist_nulls") commit 860c8802ace1 ("rcu: Use WRITE_ONCE() for assignments to ->pprev for hlist_nulls")
Reviewed-by: Kuniyuki Iwashima kuniyu@google.com Reviewed-by: Frederic Weisbecker frederic@kernel.org Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: Xuanqiang Luo luoxuanqiang@kylinos.cn Link: https://patch.msgid.link/20251015020236.431822-2-xuanqiang.luo@linux.dev Signed-off-by: Jakub Kicinski kuba@kernel.org Stable-dep-of: 1532ed0d0753 ("inet: Avoid ehash lookup race in inet_ehash_insert()") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/rculist_nulls.h | 59 +++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+)
diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h index 89186c499dd47..c26cb83ca0711 100644 --- a/include/linux/rculist_nulls.h +++ b/include/linux/rculist_nulls.h @@ -52,6 +52,13 @@ static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n) #define hlist_nulls_next_rcu(node) \ (*((struct hlist_nulls_node __rcu __force **)&(node)->next))
+/** + * hlist_nulls_pprev_rcu - returns the dereferenced pprev of @node. + * @node: element of the list. + */ +#define hlist_nulls_pprev_rcu(node) \ + (*((struct hlist_nulls_node __rcu __force **)(node)->pprev)) + /** * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization * @n: the element to delete from the hash list. @@ -152,6 +159,58 @@ static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n) n->next = (struct hlist_nulls_node *)NULLS_MARKER(NULL); }
+/** + * hlist_nulls_replace_rcu - replace an old entry by a new one + * @old: the element to be replaced + * @new: the new element to insert + * + * Description: + * Replace the old entry with the new one in a RCU-protected 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(). + */ +static inline void hlist_nulls_replace_rcu(struct hlist_nulls_node *old, + struct hlist_nulls_node *new) +{ + struct hlist_nulls_node *next = old->next; + + WRITE_ONCE(new->next, next); + WRITE_ONCE(new->pprev, old->pprev); + rcu_assign_pointer(hlist_nulls_pprev_rcu(new), new); + if (!is_a_nulls(next)) + WRITE_ONCE(next->pprev, &new->next); +} + +/** + * hlist_nulls_replace_init_rcu - replace an old entry by a new one and + * initialize the old + * @old: the element to be replaced + * @new: the new element to insert + * + * Description: + * Replace the old entry with the new one in a RCU-protected hlist_nulls, while + * permitting racing traversals, and reinitialize the old entry. + * + * Note: @old must be hashed. + * + * 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_replace_init_rcu(struct hlist_nulls_node *old, + struct hlist_nulls_node *new) +{ + hlist_nulls_replace_rcu(old, new); + WRITE_ONCE(old->pprev, NULL); +} + /** * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type * @tpos: the type * to use as a loop cursor.