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 DE34D2DC763 for ; Tue, 16 Sep 2025 01:34:35 +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=1757986478; cv=none; b=ReOc3PunITJcZVeht0arUAg4MHhF0wzUfibJswU2GxjUnSbLDq/yLCyWI+wozC4qUYnD4jpKrNIYYArAn/H6E6zPqzE5sHLp+ObxaitgnFk+DbD7aCpQdql775dLYEOGHmq+Ta/5C7nYF3l/GJKdnV/JDEcZkSQ30LMxFVhASzs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757986478; c=relaxed/simple; bh=/lQ504ZrYn7m+j2mobFcmPkr6ADpKI1SVUGF+0G3F5w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KI4bLxcC5SlbenKLqiUpnGiVDwFAoSXg97/lI/cK7PHIWekTA0Lq99/hhU949ss5bnQlsh9m3HhYBIpUHZyo2HsrmKGY5OiOyqyZks1d/Yxp5vmo76K9DLl50RxCF0PwTrlVm9ZH84eo9NS0kdpcO0owQ6UUkD9j3YPrCvEztIQ= 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=oiUNdyEQ; 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="oiUNdyEQ" Message-ID: <91b6398c-70fb-440a-a654-a3e618338134@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1757986473; 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=XDXPAsuDgTbQZNmGKDc3AXRua/2/wTL33HLJDbdMkWM=; b=oiUNdyEQSwigNjTBUu81X3S0zBfyerhLV4v+/WCpLBPYbGaS5n6j2oNOfscXPU7Td9b1cP pz0IgxNPBHrMOV5K88aeFy/auQ8px/pLoNlPDbbiBHnsri7b0VeMBQ4Ap3Z6iq4sIMzpo9 VtJ5AogHnkU55wdUTkXBWY0y2ESJfhw= Date: Tue, 16 Sep 2025 09:33:51 +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 v1 1/3] rculist: Add __hlist_nulls_replace_rcu() and hlist_nulls_replace_init_rcu() To: Kuniyuki Iwashima Cc: edumazet@google.com, kerneljasonxing@gmail.com, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, Xuanqiang Luo References: <20250915070308.111816-1-xuanqiang.luo@linux.dev> <20250915070308.111816-2-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 2025/9/16 06:50, Kuniyuki Iwashima 写道: > On Mon, Sep 15, 2025 at 12:04 AM wrote: >> From: Xuanqiang Luo >> >> Add two functions to atomically replace RCU-protected hlist_nulls entries. >> >> Signed-off-by: Xuanqiang Luo >> --- >> include/linux/rculist_nulls.h | 62 +++++++++++++++++++++++++++++++++++ >> 1 file changed, 62 insertions(+) >> >> diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h >> index 89186c499dd4..eaa3a0d2f206 100644 >> --- a/include/linux/rculist_nulls.h >> +++ b/include/linux/rculist_nulls.h >> @@ -152,6 +152,68 @@ 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)) { > This is already checked by __sk_nulls_replace_node_init_rcu(). > It seems to me that hlist_nulls_replace_init_rcu() checks whether the sk_nulls_node is unhashed, while __sk_nulls_replace_node_init_rcu() checks the sk_node's unhashed status. Perhaps these serve different purposes? This would maintain parity with how hlist_nulls_del_init_rcu verifies sk_nulls_node and __sk_nulls_del_node_init_rcu() checks sk_node. Thanks Xuanqiang >> + __hlist_nulls_replace_rcu(old, new); >> + 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. >> -- >> 2.27.0 >>