From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) (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 B416D28724C for ; Fri, 26 Sep 2025 07:41:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758872497; cv=none; b=AtWbyouhotQ0Av+Az8dN+9HakdnRy9StIBinF39vQYbrHqzrdxqHehOvhyMEAzOBJu1lvZmwklJ+lARTqOR4q++kF0QWZd/8BM0BBZrpWR6a6SpiQ3x/YgfKVOUVPqi0ha7+iLg4GAP3Grik9Or0KQ79bDsG2/khAA+Csa+keug= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758872497; c=relaxed/simple; bh=z54J7IGZwbaq89V3MtbkWW9kJ+KdZ2FSjnd8NDKMEak=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Qi3PeVbYQY9E8dsfrbC3lOzO8UuJrhqCIGmRxrjSYLCiJHuvNhFthh+8FH+FUxSoprGKpi/3QlUQukeidc2x7PDlg8Qw8yQq1vXynKfurxH3Q2ehut6Y9bjuDXRnnBgXQSfIce8HDOi08Rg/w5IyLzslV+aDaeyDR3SBdZ5sLqU= 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=oqZrgIa8; arc=none smtp.client-ip=95.215.58.181 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="oqZrgIa8" 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=1758872493; 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=0TESBl5zoUY/MzgnymC1k0ZH+31XZPacA8yk+AIRCd8=; b=oqZrgIa8bXXnbGmV7Pm63urfJxSS6ADIF+1G2JVAeXnuQFXd9eE/cy5yeDXiB2IztIJ61b vrSPyj9WqrbBouj7FP8mB35BSwFdRQ7xYAfoK7HuNrfMUdNx7Edj1gKm6C6c9braIZN4Jr wWI+r4CM7eKRdQ5FCCOaFMp90Jy43pM= From: xuanqiang.luo@linux.dev To: edumazet@google.com, kuniyu@google.com, "Paul E. McKenney" Cc: kerneljasonxing@gmail.com, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, Xuanqiang Luo , Frederic Weisbecker , Neeraj Upadhyay Subject: [PATCH net-next v7 1/3] rculist: Add hlist_nulls_replace_rcu() and hlist_nulls_replace_init_rcu() Date: Fri, 26 Sep 2025 15:40:31 +0800 Message-Id: <20250926074033.1548675-2-xuanqiang.luo@linux.dev> In-Reply-To: <20250926074033.1548675-1-xuanqiang.luo@linux.dev> References: <20250926074033.1548675-1-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: 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") Signed-off-by: Xuanqiang Luo --- 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 89186c499dd4..c26cb83ca071 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. -- 2.25.1