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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 DF2EBC46475 for ; Tue, 23 Oct 2018 06:49:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9C0F52075D for ; Tue, 23 Oct 2018 06:49:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="qpQ3hvz1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9C0F52075D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com 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 S1727665AbeJWPLL (ORCPT ); Tue, 23 Oct 2018 11:11:11 -0400 Received: from mail-pf1-f193.google.com ([209.85.210.193]:43658 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727430AbeJWPLL (ORCPT ); Tue, 23 Oct 2018 11:11:11 -0400 Received: by mail-pf1-f193.google.com with SMTP id q1-v6so187201pfh.10 for ; Mon, 22 Oct 2018 23:49:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=VEL8NGCX26YMWuOF6kPKplHgOkj/akorRDar1Ylbxd4=; b=qpQ3hvz1LKiYe0C9891nqdTM4gtgsUpuQUH/8NNCRhazdYtPVxD9/NuML1WPsClgz3 3Qill82dDJJOU5pXYkRVMWS+r7txo5mY1FmollvwKpHbMWXASbedZbkPEOdjRwO+n1Op HHjTXNIJZsBk1OQ3pXrjTLYliWZu2+sFpJyeM7JmkYbZANCCZs/0etKBLrq0M/htLpZg dBPdgbAPCGf1J3pBaGRiZ4Te7rdRoLSqY3HkbTMsdXlfgvR8pEjMeoRTmiBpyhQwQZf2 84NrcMi8E2Ve2PkSnL/L0TwaqgBfmznJjB3Yh7dt77joBKUmJT+5YZrdy7NgUjdF8YiO CFag== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=VEL8NGCX26YMWuOF6kPKplHgOkj/akorRDar1Ylbxd4=; b=V9TI1IGFuHTFKYcF4+zW64+rnrnIrGQpAY96YBFUULlaYBWWCpJrRgbKHqoSO4l90J yaXviKsDSk0/ihfVZ3VdUfyJYuvi64spuTZjww9KkM5AUEFj7kTfDN8+fS8zyh5FI1xm aM1jPI0H+9AkG+8uz4r329FQ16igD8neiLkDUvD5u8SuWdz6AslIn3zymLoSploXZvuS YDCG1wSRC2B8fKdMBTfjCS9MqPqdX6sZDhY5+AqZN270cEB1SAzMu0JNLsTp0wPx3Uwk gT94NJNr8jgfDrDIfNXAsymQ5Rl7d0Hs3MHQlUHrz95QmvH1MIqI3qZdXFvVbBFg3Tsw q1lA== X-Gm-Message-State: ABuFfohbXLR5kjWX2NeFi/E/EEGZlRIEGbCQwvjm8Yqc2Gx9/MsS3miK 5YHSkpVL0++XT+5xH+sAoik= X-Google-Smtp-Source: ACcGV60ZabuJfjufdoVKmSkT435hsZdu6QbvSKm32OMfv2b9ZQrILL3TMnyyJYhYnAEB99mtesUlog== X-Received: by 2002:a63:a40a:: with SMTP id c10-v6mr46521420pgf.140.1540277348694; Mon, 22 Oct 2018 23:49:08 -0700 (PDT) Received: from localhost ([175.223.11.183]) by smtp.gmail.com with ESMTPSA id i4-v6sm587580pgt.4.2018.10.22.23.49.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 22 Oct 2018 23:49:07 -0700 (PDT) Date: Tue, 23 Oct 2018 15:49:04 +0900 From: Sergey Senozhatsky To: Steven Rostedt Cc: Sergey Senozhatsky , Petr Mladek , Linus Torvalds , LKML , Peter Zijlstra , Andrew Morton , Thomas Gleixner , Ingo Molnar Subject: Re: NMI watchdog dump does not print on hard lockup Message-ID: <20181023064904.GB504@jagdpanzerIV> References: <20171012121658.187c5af6@gandalf.local.home> <20171013111444.GB2795@pathway.suse.cz> <20171013091857.4afe8a7a@gandalf.local.home> <20171016111239.GK2795@pathway.suse.cz> <20171016131305.GE6316@tigerII.localdomain> <20171016101547.27b4aa11@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171016101547.27b4aa11@gandalf.local.home> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (10/16/17 10:15), Steven Rostedt wrote: > On Mon, 16 Oct 2017 22:13:05 +0900 > Sergey Senozhatsky wrote: > > > just "brainstorming" it... with some silly ideas. > > > > pushing the data from NMI panic might look like we are replacing one > > deadlock scenario with another deadlock scenario. some of the console > > drivers are soooo complex internally. so I have been thinking about... > > may be we can extend struct console and add ->write_on_panic() and that > > handler must be as lockless as possible; so lockless that calling it > > from anything that is not panic() is a severe bug. > > This may not be a bad idea. And make it so it can't be called unless we > are in panic mode (or at least "oops in progress"). > > If oops_in_progress is set, and the console has a "write_on_panic" > handler, then just call that. Good news Steven. It turned out that some of serial consoles already have this write_on_panic() mechanism enabled. Such consoles have the following thing is their usual ->write() callbacks (which we call from printk()): static void serial_console_write(struct console *co, const char *s, unsigned count) { ... if (port->sysrq) locked = 0; else if (oops_in_progress) locked = spin_trylock_irqsave(&port->lock, flags); else spin_lock_irqsave(&port->lock, flags); ... uart_console_write(port, s, count, serial_console_putchar); ... if (locked) spin_unlock_irqrestore(&port->lock, flags); } Notice the special handling of port->sysrq and oops_in_progress cases. So we, basically, already have "lockless on panic" serial consoles. The problem is - it seems that panic() does not always let lockless consoles to be lockless. I'm trying to address this in [1]. [1] lkml.kernel.org/r/20181016050428.17966-2-sergey.senozhatsky@gmail.com -ss