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=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 97791C2D0A3 for ; Mon, 2 Nov 2020 03:14:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 617D42224E for ; Mon, 2 Nov 2020 03:14:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727839AbgKBDOn (ORCPT ); Sun, 1 Nov 2020 22:14:43 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:7393 "EHLO szxga07-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727800AbgKBDOn (ORCPT ); Sun, 1 Nov 2020 22:14:43 -0500 Received: from DGGEMS411-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4CPdLm1BKbz6yxB; Mon, 2 Nov 2020 11:14:40 +0800 (CST) Received: from [10.74.191.121] (10.74.191.121) by DGGEMS411-HUB.china.huawei.com (10.3.19.211) with Microsoft SMTP Server id 14.3.487.0; Mon, 2 Nov 2020 11:14:32 +0800 Subject: Re: [PATCH net-next] net: add in_softirq() debug checking in napi_consume_skb() To: Jakub Kicinski CC: , , , , , , , , , , , , , , , References: <1603971288-4786-1-git-send-email-linyunsheng@huawei.com> <20201031153824.7ae83b90@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net> From: Yunsheng Lin Message-ID: <5b04ad33-1611-8d7b-8fec-4269c01ecab3@huawei.com> Date: Mon, 2 Nov 2020 11:14:32 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20201031153824.7ae83b90@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.74.191.121] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/11/1 6:38, Jakub Kicinski wrote: > On Thu, 29 Oct 2020 19:34:48 +0800 Yunsheng Lin wrote: >> The current semantic for napi_consume_skb() is that caller need >> to provide non-zero budget when calling from NAPI context, and >> breaking this semantic will cause hard to debug problem, because >> _kfree_skb_defer() need to run in atomic context in order to push >> the skb to the particular cpu' napi_alloc_cache atomically. >> >> So add a in_softirq() debug checking in napi_consume_skb() to catch >> this kind of error. >> >> Suggested-by: Eric Dumazet >> Signed-off-by: Yunsheng Lin > >> diff --git a/net/core/skbuff.c b/net/core/skbuff.c >> index 1ba8f01..1834007 100644 >> --- a/net/core/skbuff.c >> +++ b/net/core/skbuff.c >> @@ -897,6 +897,10 @@ void napi_consume_skb(struct sk_buff *skb, int budget) >> return; >> } >> >> + DEBUG_NET_WARN(!in_softirq(), >> + "%s is called with non-zero budget outside softirq context.\n", >> + __func__); > > Can't we use lockdep instead of defining our own knobs? >From the first look, using the below seems better than defining our own knobs, because there is similar lockdep_assert_in_irq() checking already and lockdep_assert_in_*() is NULL-OP when CONFIG_PROVE_LOCKING is not defined. > > Like this maybe? > > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h > index f5594879175a..5253a167d00c 100644 > --- a/include/linux/lockdep.h > +++ b/include/linux/lockdep.h > @@ -594,6 +594,14 @@ do { \ > this_cpu_read(hardirqs_enabled))); \ > } while (0) > > +#define lockdep_assert_in_softirq() \ > +do { \ > + WARN_ON_ONCE(__lockdep_enabled && \ > + (softirq_count() == 0 || \ > + this_cpu_read(hardirq_context))); \ Using in_softirq() seems more obvious then using softirq_count()? And there is below comment above avoiding the using of in_softirq(), maybe that is why you use softirq_count() directly here? "softirq_count() == 0" still mean we are not in the SoftIRQ context and BH is not disabled. right? Perhap lockdep_assert_in_softirq_or_bh_disabled() is more obvious? /* * Are we doing bottom half or hardware interrupt processing? * * in_irq() - We're in (hard) IRQ context * in_softirq() - We have BH disabled, or are processing softirqs * in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled * in_serving_softirq() - We're in softirq context * in_nmi() - We're in NMI context * in_task() - We're in task context * * Note: due to the BH disabled confusion: in_softirq(),in_interrupt() really * should not be used in new code. */ Also, is there any particular reason we do the "this_cpu_read(hardirq_context)" checking? Thanks. > +} while (0) > > > >> if (!skb_unref(skb)) >> return; >> > > . >