From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D53DEC433DB for ; Mon, 15 Mar 2021 23:43:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 89FA764F5E for ; Mon, 15 Mar 2021 23:43:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233455AbhCOXmc (ORCPT ); Mon, 15 Mar 2021 19:42:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:33811 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230455AbhCOXmC (ORCPT ); Mon, 15 Mar 2021 19:42:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615851721; 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=I8p0ewYrXjBd6YhOPwSyL1Y4ews+TOxljgNaVhrVMaM=; b=eUmO2hxNOt8+FXrjeBS0GSC2eVTp4VzLTEVSTuN51HyLcpicBPxsJackmW3OYQwYQyMDGg Ey3l72BxqWRTjp4j0+OfSX5CuwrDH/SQz5gf2e2BBfm+VKAjB1sHI5Irp4Or+Gj4lrdeyw RGQQetQRWKRAkWmFM5XA9wHvPBjqbkg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-418-7lR3_wmhOPq1fU53TqAdDw-1; Mon, 15 Mar 2021 19:41:57 -0400 X-MC-Unique: 7lR3_wmhOPq1fU53TqAdDw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 70FF5100C619; Mon, 15 Mar 2021 23:41:55 +0000 (UTC) Received: from localhost (unknown [10.10.110.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id ED3165B4A8; Mon, 15 Mar 2021 23:41:52 +0000 (UTC) Date: Mon, 15 Mar 2021 16:41:51 -0700 (PDT) Message-Id: <20210315.164151.1093629330365238718.davem@redhat.com> To: linyunsheng@huawei.com Cc: kuba@kernel.org, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@openeuler.org Subject: Re: [PATCH net-next] net: sched: remove unnecessay lock protection for skb_bad_txq/gso_skb From: David Miller In-Reply-To: <1615800610-34700-1-git-send-email-linyunsheng@huawei.com> References: <1615800610-34700-1-git-send-email-linyunsheng@huawei.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yunsheng Lin Date: Mon, 15 Mar 2021 17:30:10 +0800 > Currently qdisc_lock(q) is taken before enqueuing and dequeuing > for lockless qdisc's skb_bad_txq/gso_skb queue, qdisc->seqlock is > also taken, which can provide the same protection as qdisc_lock(q). > > This patch removes the unnecessay qdisc_lock(q) protection for > lockless qdisc' skb_bad_txq/gso_skb queue. > > And dev_reset_queue() takes the qdisc->seqlock for lockless qdisc > besides taking the qdisc_lock(q) when doing the qdisc reset, > some_qdisc_is_busy() takes both qdisc->seqlock and qdisc_lock(q) > when checking qdisc status. It is unnecessary to take both lock > while the fast path only take one lock, so this patch also changes > it to only take qdisc_lock(q) for locked qdisc, and only take > qdisc->seqlock for lockless qdisc. > > Since qdisc->seqlock is taken for lockless qdisc when calling > qdisc_is_running() in some_qdisc_is_busy(), use qdisc->running > to decide if the lockless qdisc is running. > > Signed-off-by: Yunsheng Lin What about other things protected by this lock, such as statistics and qlen? This change looks too risky to me.