From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (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 9090B2472BB for ; Fri, 26 Sep 2025 03:23:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758857028; cv=none; b=PtzavR0kZz0h0iSRcVm5XEih7f1isgVOj2HGL2lbKRUsvD46VEN80GPiBiRZK5vx+aQn8z7CrXw8fJR3VOhcuN4F3RQxqbf6c5SwRx0AwqpcN4zQ0ZZUfkFrWjY4B/SvqkDdJppKtXbGHbX/h0lBNb2UShbBe2JLf7L0u7pwKvM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758857028; c=relaxed/simple; bh=r/re+tLu9QoexP4hij7b/mWnQppcIqtrPGWNgPLcRm0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ehr4py6pyzBbkus14YSHDAqxCoW1pv9zyofJWFw9OD4J01rshUmjtGV6ivGXGxgRjeskUaFHjSfJ+74gOYLjJWIq+oqm1nStZx4hWz6w2n2aFmelAqcMU3IVFsWXWc4cnq9gdcy0MpM3X5FxG6VB4Rv6l4J87a24Nc8SX38wtb8= 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=Zpm5Rpoh; arc=none smtp.client-ip=91.218.175.173 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="Zpm5Rpoh" Message-ID: <5d7904e8-977e-499c-b877-901facac5dea@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758857023; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=d9ZpWAXCOpje0ckd48jmEPyNBT6W15BRdmzJEt9Sy9Q=; b=Zpm5RpohAr1xLOTDrz20H6pVZJaEU7YMcgHdSoggSX+v0Bkr1cFVtjU2qWqqreC2BxzOAU DiW8SzhRuZyhUIFosfCN48WjdmxksygvXkG5OvzUEvJ6QaQh2eDLVRe1EPC7P5vE5e19CV EtE3Y6oBskowCMqyasrshyohm18Al98= Date: Fri, 26 Sep 2025 11:23:02 +0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH net-next v6 1/3] rculist: Add hlist_nulls_replace_rcu() and hlist_nulls_replace_init_rcu() To: Kuniyuki Iwashima Cc: edumazet@google.com, "Paul E. McKenney" , kerneljasonxing@gmail.com, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, Xuanqiang Luo , Frederic Weisbecker , Neeraj Upadhyay References: <20250925021628.886203-1-xuanqiang.luo@linux.dev> <20250925021628.886203-2-xuanqiang.luo@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: luoxuanqiang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2025/9/26 01:56, Kuniyuki Iwashima 写道: > On Wed, Sep 24, 2025 at 7:18 PM wrote: >> 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 | 52 +++++++++++++++++++++++++++++++++++ >> 1 file changed, 52 insertions(+) >> >> diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h >> index 89186c499dd4..c3ba74b1890d 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) > nit: checkpatch complains here.. > https://patchwork.kernel.org/project/netdevbpf/patch/20250925021628.886203-2-xuanqiang.luo@linux.dev/ > > CHECK: Alignment should match open parenthesis > #46: FILE: include/linux/rculist_nulls.h:171: > +static inline void hlist_nulls_replace_rcu(struct hlist_nulls_node *old, > + struct hlist_nulls_node *new) Thanks for pointing it out, I'll fix it in the next version. Appreciate it! > >> +{ >> + 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); > nit: define hlist_nulls_prev_rcu() like hlist_nulls_next_rcu(). I'm wondering if defining a macro called hlist_nulls_prev_rcu() might be controversial, since it should actually be getting the prev->next rather than the prev itself. Would it be more appropriate to rename it to hlist_nulls_prev_next_rcu() instead? Like this: diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h index c3ba74b1890d..9399ec9dc82d 100644 --- a/include/linux/rculist_nulls.h +++ b/include/linux/rculist_nulls.h @@ -52,6 +52,14 @@ 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_prev_next_rcu - returns the next pointer of the previous + * element. + * @node: element of the list. + */ +#define hlist_nulls_prev_next_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. However, I noticed that in the definition of hlist_pprev_rcu(), it directly uses pprev: #define hlist_pprev_rcu(node)    (*((struct hlist_node __rcu **)((node)->pprev))) This part seems a bit confusing to me. It's possible I'm missing some historical context here. If so, please feel free to point it out. Thanks! > >> + if (!is_a_nulls(next)) >> + WRITE_ONCE(new->next->pprev, &new->next); > nit: s/new->next->pprev/next->pprev/ I'll update it in the next version. Thank you! >> +} >> + >> +/** >> + * 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 >>