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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT 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 C6FD7C04EB8 for ; Fri, 30 Nov 2018 18:04:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 995C42146F for ; Fri, 30 Nov 2018 18:04:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 995C42146F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726815AbeLAFO4 (ORCPT ); Sat, 1 Dec 2018 00:14:56 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:38553 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726409AbeLAFO4 (ORCPT ); Sat, 1 Dec 2018 00:14:56 -0500 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1gSn9f-0008Qr-IH; Fri, 30 Nov 2018 19:04:43 +0100 Date: Fri, 30 Nov 2018 19:04:43 +0100 From: Sebastian Andrzej Siewior To: Steven Rostedt , Nikolay Aleksandrov Cc: Oleksandr Natalenko , "David S. Miller" , Thomas Gleixner , Eric Dumazet , Dave Jones , netdev@vger.kernel.org, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: WARN_ON() in netconsole with PREEMPT_RT Message-ID: <20181130180443.o2kjcpweaglmsmx6@linutronix.de> References: <20181111210105.7f376c35@vmware.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181111210105.7f376c35@vmware.local.home> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018-11-11 21:01:05 [-0500], Steven Rostedt wrote: > On Sun, 11 Nov 2018 21:16:00 +0100 > Oleksandr Natalenko wrote: > > Oh, I see that write_msg() calls netpoll_send_udp() under > > spin_lock_irqsave(), but in PREEMPT_RT this, AFAIK, does not disable > > interrupts. > > > > So, the real question here is whether the interrupts should be indeed > > disabled. And if so, -rt should replace spin_lock_irqsave() call there > > with what? local_irq_save()? and get rid of the warning? > > > > Why do we care if interrupts are disabled with PREEMPT_RT here? We don't actually. It was broken before for some reason and disabled on RT. Later people asked for NETCONSOLE on RT and it seemed to have worked so I allowed it again starting with v3.14.3-rt5. A year later (v4.3-rc1) commit c9fd56b34efd0 ("netpoll: warn on netpoll_send_udp users who haven't disabled irqs") introduced that warning. It seems the only reason why netpoll_send_udp() is invoked with disabled interrupts is because the caller acquired `target_list_lock' with disabled interrupts. I remember that earlier there was some local_irq_save() based locking but all this is gone now. Nikolay could you please explain why interrupts have to be disabled at this point? It looks to me that this check could be dropped. > -- Steve Sebastian