From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) (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 16CD823D283 for ; Tue, 16 Sep 2025 06:47:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758005232; cv=none; b=X+ptj4e8WqRTgh2/F1tNs6RBHuAmOXcTJryVMWEkXxq81a5dqvH49OoAN19VMFWXXk1UATtLxfaUP3NRvnLuux4O36MOD5z7HIV7jH8Xeo04Qm0u/QvUf4OGygQDcM9EZ47F6Y0jBhCByF5ddPqzLb5HVxuy+PunjgjsyZMi8ho= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758005232; c=relaxed/simple; bh=e2Och8MCNRVJ2HqPs7A28h0GKMf4Vc3xffz2+8mv0e0=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=eWFhF6aUvM2ICsio6R+OSv4iDctHJqLqlJ7rlKZIMxgp39mYsvQfHBhGjBKSe8er5s4iEImJDozL22TqDUimZBtEB3sMYCCWOFl4l8DusQ/RBxkmmnOlEGLtFVGjq+Gfi/HJ5k+QU62k/PKygUO9gI5uOA/KbGKJPKkQ4Cq5HU8= 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=fYLziVqc; arc=none smtp.client-ip=91.218.175.177 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="fYLziVqc" 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=1758005226; 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=T8uH/d61lIzsXarIEdO6A+UL33AK9E0ycEfJKcpiYbk=; b=fYLziVqcl7neDH+U9CUKsFZ5F1qedt+FMWgv2oohoGW8wKWHDmv+n/bz11/OKio98kTR2n Np5lsJk/9KZ4wDGyBXiyOGfKEIfFgjodREZ7r6MED6drhdbTFrrBbLRl3VqEdNYazPQ/4p gBu49oCJopv7p9OSwvx3ytRuzEwB5jk= 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 v2 1/3] rculist: Add __hlist_nulls_replace_rcu() and hlist_nulls_replace_init_rcu() Date: Tue, 16 Sep 2025 14:46:12 +0800 Message-Id: <20250916064614.605075-2-xuanqiang.luo@linux.dev> In-Reply-To: <20250916064614.605075-1-xuanqiang.luo@linux.dev> References: <20250916064614.605075-1-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. Signed-off-by: Xuanqiang Luo --- include/linux/rculist_nulls.h | 61 +++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h index 89186c499dd4..8ed604f65a3e 100644 --- a/include/linux/rculist_nulls.h +++ b/include/linux/rculist_nulls.h @@ -152,6 +152,67 @@ 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; + + 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. + * + * Return: true if the old entry was hashed and was replaced successfully, false + * otherwise. + * + * Note: hlist_nulls_unhashed() on the old node returns 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. + * + * 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 bool hlist_nulls_replace_init_rcu(struct hlist_nulls_node *old, + struct hlist_nulls_node *new) +{ + if (!hlist_nulls_unhashed(old)) { + __hlist_nulls_replace_rcu(old, new); + WRITE_ONCE(old->pprev, NULL); + return true; + } + return false; +} + /** * 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