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 Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 07804C54E49 for ; Thu, 7 Mar 2024 17:27:32 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Ayz90ujO; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4TrGTH3Nn2z3vZD for ; Fri, 8 Mar 2024 04:27:31 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Ayz90ujO; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.dev (client-ip=91.218.175.173; helo=out-173.mta0.migadu.com; envelope-from=sean.anderson@linux.dev; receiver=lists.ozlabs.org) Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4TrGSR1YwJz3bnv for ; Fri, 8 Mar 2024 04:26:44 +1100 (AEDT) Message-ID: <49ca7920-d429-434a-aede-1a200e8d5ce8@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1709832381; 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=typJzsyCZ7d0N2AWtsRnRkkZEuqyJ1S5uCH3hrAdMlA=; b=Ayz90ujO9VGGPBPBUzhJG/0z3frrtSSosfU6bd3HdfMioTtavGW2EUkG1Ej2q8KtTF8siq RiawcerkWVH1IqmUaJplOxSyFkFQ6Pu5Pbk+Kpe8G0KcewTfjN36YOsuCYE3oGj2f4d4Q5 tQ5GrYK9qaIeKxKrjhRKtUdwZsGwHTM= Date: Thu, 7 Mar 2024 12:26:00 -0500 MIME-Version: 1.0 Subject: Re: [RESEND2 PATCH net v4 2/2] soc: fsl: qbman: Use raw spinlock for cgr_lock Content-Language: en-US To: Christophe Leroy , "David S . 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From: Sean Anderson In-Reply-To: <63ab7b62-853c-4996-a493-465283252d5a@csgroup.eu> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Vladimir Oltean , Roy Pledge , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , Li Yang , Scott Wood , Claudiu Manoil , Camelia Groza , Steffen Trumtrar , "linuxppc-dev@lists.ozlabs.org" , "linux-arm-kernel@lists.infradead.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 3/5/24 17:18, Christophe Leroy wrote: > > > Le 05/03/2024 à 19:14, Sean Anderson a écrit : >> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ] >> >> Hi, >> >> On 2/23/24 11:02, Sean Anderson wrote: >>> On 2/23/24 00:38, Christophe Leroy wrote: >>>> Le 22/02/2024 à 18:07, Sean Anderson a écrit : >>>>> [Vous ne recevez pas souvent de courriers de sean.anderson@linux.dev. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ] >>>>> >>>>> cgr_lock may be locked with interrupts already disabled by >>>>> smp_call_function_single. As such, we must use a raw spinlock to avoid >>>>> problems on PREEMPT_RT kernels. Although this bug has existed for a >>>>> while, it was not apparent until commit ef2a8d5478b9 ("net: dpaa: Adjust >>>>> queue depth on rate change") which invokes smp_call_function_single via >>>>> qman_update_cgr_safe every time a link goes up or down. >>>> >>>> Why a raw spinlock to avoid problems on PREEMPT_RT, can you elaborate ? >>> >>> smp_call_function always runs its callback in hard IRQ context, even on >>> PREEMPT_RT, where spinlocks can sleep. So we need to use raw spinlocks >>> to ensure we aren't waiting on a sleeping task. See the first bug report >>> for more discussion. >>> >>> In the longer term it would be better to switch to some other >>> abstraction. >> >> Does this make sense to you? > > Yes that fine, thanks for the clarification. Maybe you can explain that > in the patch description in case you send a v5. Hm, I thought I put this description in the commit message already. Maybe something like | smp_call_function always runs its callback in hard IRQ context, even on | PREEMPT_RT, where spinlocks can sleep. So we need to use a raw spinlock | for cgr_lock to ensure we aren't waiting on a sleeping task. | | Although this bug has existed for a while, it was not apparent until | commit ef2a8d5478b9 ("net: dpaa: Adjust queue depth on rate change") | which invokes smp_call_function_single via qman_update_cgr_safe every | time a link goes up or down. would be clearer. --Sean