From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (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 A3F7E2FB081 for ; Sat, 20 Sep 2025 11:00:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758366036; cv=none; b=UElnInoYTJj7Oib+UhAnAnonLSHGoJCWXF7wACd+OSiK08is3r2U+tHrPc7DhoramYZE+49NBD0egRnUARMlElPrNALZ/C5r3DjQJmL49h65HuS/8ZcaoIRn4NpH5uJT0P8jnZzYnuD9L3H1WmCzcL717rRGlQrdHhm0RWdGCYo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758366036; c=relaxed/simple; bh=/XMSjictOBgg582eI3BE8xwZ4/2QciaBNjl3jbfV/Ag=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=k/K/Nh4HmKf2jWk4GLuqCY075z9NUTl5AgaT8Xx2Inmgr+bBrOSospqOcPKJr65zs98yHSdqncXQe6a/A/gUF4W1i0pA5ipPIMj/z293hkKNEYghp1VvkgSsN1MGywtLfY9Vb66BF+Ya41tmXGUWpPfASc2BQn5PcMdAIEea/BE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=vGkbRl8N; arc=none smtp.client-ip=95.215.58.186 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="vGkbRl8N" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758366032; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/I/FicWToQ7Vtn+zNVYEIskS32QQ4uRRthzz4WyJizA=; b=vGkbRl8NRIAcdnm2rkTH/toOwvTTgzW9QFGz2dGGiav5P/1qqJrKtljOZZ6zY+RoFedGCh ftvNjPe1PX/B+O0RGbLGLb8pDyNdSaP8WzdXCiJwXpjkKIdhiYfve2NiaWs0J3OxGHB+25 npe83gMQy7a3tFxIZuqo0mu1lQiHDn4= From: xuanqiang.luo@linux.dev To: edumazet@google.com, kuniyu@google.com Cc: kerneljasonxing@gmail.com, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, Xuanqiang Luo Subject: [PATCH net-next v4 1/3] rculist: Add __hlist_nulls_replace_rcu() and hlist_nulls_replace_init_rcu() Date: Sat, 20 Sep 2025 18:59:43 +0800 Message-Id: <20250920105945.538042-2-xuanqiang.luo@linux.dev> In-Reply-To: <20250920105945.538042-1-xuanqiang.luo@linux.dev> References: <20250920105945.538042-1-xuanqiang.luo@linux.dev> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Xuanqiang Luo 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: efd04f8a8b45 ("rcu: Use WRITE_ONCE() for assignments to ->next for rculist_nulls") 860c8802ace1 ("rcu: Use WRITE_ONCE() for assignments to ->pprev for hlist_nulls") Signed-off-by: Xuanqiang Luo --- include/linux/rculist_nulls.h | 52 +++++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h index 89186c499dd4..d86331ce22c4 100644 --- a/include/linux/rculist_nulls.h +++ b/include/linux/rculist_nulls.h @@ -152,6 +152,58 @@ 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(*(struct hlist_nulls_node __rcu **)new->pprev, new); + if (!is_a_nulls(next)) + WRITE_ONCE(new->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 should 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. -- 2.25.1