From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.netfilter.org (mail.netfilter.org [217.70.190.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EC65221CC5C for ; Mon, 20 Apr 2026 06:19:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.190.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776665975; cv=none; b=sdwWdxVe01OaIV7znHSnYyYPyNxhhdMUehk+De2JEOKkp+jbb6RwiXmcM4tFOPhYgLaDvq0VBBmw//JaBgCNS5TAwec3ITzOJxDXyOqlj3VBimi2iu0RWMOoDj2YwuInQ4qLPxs4J5JWBLh/OxFzVfRuOnizwWxOH6NSltG0ALE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776665975; c=relaxed/simple; bh=n82jOt6UEQC7+N0W8gYIzx30WEx1rR+0cYIp6zIdwf8=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jYznfw8xZqch1rIpI8//IWWouWdX/vKnGZqIM7tqvn+yqXcxtzu9VRBxm5657p+N+8MO5Qg/Lc+/7gMaWAtKSBLbDjYgsYSl1CD8NxYhsI0qnNWBAgBVGYho2TBmjtx2alYeb8GcjpvHqhvlWTkKD9DoMAfSaecUGmJbg68WmOQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=netfilter.org; spf=pass smtp.mailfrom=netfilter.org; dkim=pass (2048-bit key) header.d=netfilter.org header.i=@netfilter.org header.b=iM9D6qsE; arc=none smtp.client-ip=217.70.190.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=netfilter.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=netfilter.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=netfilter.org header.i=@netfilter.org header.b="iM9D6qsE" Received: from localhost.localdomain (mail-agni [217.70.190.124]) by mail.netfilter.org (Postfix) with ESMTPSA id E6432602B1 for ; Mon, 20 Apr 2026 08:19:30 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=netfilter.org; s=2025; t=1776665971; bh=o8VaDYQ2e6Gez2TNQ38DdiCZe12qY8iiXBtviqCYhfM=; h=From:To:Subject:Date:In-Reply-To:References:From; b=iM9D6qsEPIpudDOc9iUg1fu46wisUCnvhqr1dGeUt16Iqqu/CNm722QbSxjeRf4iE teoAX729GqFHD8u1rsZoq7TrlicNgTvBhus1KYxW8yelobFBInmTbGLsB/zMRUKImq ZrtYqbyYujW+q268g42H5zfALnnOqVjnt8sFUapy4S5nQW7+N88PSz5VpD5ak3tUse Ng4c49R9v5RlkxW5fW/IQmAWo8d7TK+fy5YGvcvms7ps+jqTyGLSX/AsPEFF+pZjpg nYXreWmvx+NNJfoDaUMlFEI7gDhZNuVjuJG1elPUGg6Ht9KdXzBCXnHvxLwJWeFgp7 7PAeMHhTIXsmQ== From: Pablo Neira Ayuso To: netfilter-devel@vger.kernel.org Subject: [PATCH nf,v7 2/4] rculist: add list_splice_rcu() for private lists Date: Mon, 20 Apr 2026 08:19:22 +0200 Message-ID: <20260420061924.69302-2-pablo@netfilter.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260420061924.69302-1-pablo@netfilter.org> References: <20260420061924.69302-1-pablo@netfilter.org> Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This patch adds a helper function, list_splice_rcu(), to safely splice a private (non-RCU-protected) list into an RCU-protected list. The function ensures that only the pointer visible to RCU readers (prev->next) is updated using rcu_assign_pointer(), while the rest of the list manipulations are performed with regular assignments, as the source list is private and not visible to concurrent RCU readers. This is useful for moving elements from a private list into a global RCU-protected list, ensuring safe publication for RCU readers. Subsystems with some sort of batching mechanism from userspace can benefit from this new function. The function __list_splice_rcu() has been added for clarity and to follow the same pattern as in the existing list_splice*() interfaces, where there is a check to ensure that the list to splice is not empty. Note that __list_splice_rcu() has no documentation for this reason. Reviewed-by: Paul E. McKenney Signed-off-by: Pablo Neira Ayuso --- include/linux/rculist.h | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 2abba7552605..e3bc44225692 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -261,6 +261,35 @@ static inline void list_replace_rcu(struct list_head *old, old->prev = LIST_POISON2; } +static inline void __list_splice_rcu(struct list_head *list, + struct list_head *prev, + struct list_head *next) +{ + struct list_head *first = list->next; + struct list_head *last = list->prev; + + last->next = next; + first->prev = prev; + next->prev = last; + rcu_assign_pointer(list_next_rcu(prev), first); +} + +/** + * list_splice_rcu - splice a non-RCU list into an RCU-protected list, + * designed for stacks. + * @list: the non RCU-protected list to splice + * @head: the place in the existing RCU-protected list to splice + * + * The list pointed to by @head can be RCU-read traversed concurrently with + * this function. + */ +static inline void list_splice_rcu(struct list_head *list, + struct list_head *head) +{ + if (!list_empty(list)) + __list_splice_rcu(list, head, head->next); +} + /** * __list_splice_init_rcu - join an RCU-protected list into an existing list. * @list: the RCU-protected list to splice -- 2.47.3