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=-2.4 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 656D0C43219 for ; Tue, 30 Apr 2019 05:29:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 284D92075E for ; Tue, 30 Apr 2019 05:29:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="kQeS2G8T" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726144AbfD3F3x (ORCPT ); Tue, 30 Apr 2019 01:29:53 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:36742 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725446AbfD3F3w (ORCPT ); Tue, 30 Apr 2019 01:29:52 -0400 Received: by mail-wr1-f67.google.com with SMTP id o4so7454536wra.3 for ; Mon, 29 Apr 2019 22:29:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=gByLVW4J/Gu3P/aWPaRVqL5VGCmvIntSLMMQS5bvR/w=; b=kQeS2G8TyW2r1LQJAVwbM6r1oO0BT3kSyYw8aA2eTK9poPfUdZFbFMzz668WyBNt+M CSfnuNTrhVLdqFtkNDdbNjsa+oHd32lgKj4BptLYlqKaivRSmidaRr59N5PwxRfyKCf7 YJgZPSCjLWoJyhEDAVQeWZEGj4M3b35Ss1HgL/WZn7L/TFfOq19LzTUUENkPgI9RrDIm m7T8lK3LS0K5vwmtO8iZj+U28Te89zefsXd78eEW5v/Qcn7ZBuDzwcHGLqRi5tRglGyD JDX3HBO3ElGVeE3m0JWSmiI6DR+4YxGfbnJxQv4KybHKktec06iQz4gdk8oOWleNNyaq eIOg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=gByLVW4J/Gu3P/aWPaRVqL5VGCmvIntSLMMQS5bvR/w=; b=cTdcmRMfOb5frm1YR5rfZxIKfeKOXFqwzp+t/MmQg1Jv1oTY0dilhNB0hDVEgD9Sdc lhlA7Ysl1ecAoFu9zyghZjIeOfygVtyuiiI1Xvu97EnIyTWDD/aADRgfkv0E5249vC3t bDSIsq98OeUwpEbjWaRWzi5tm4C4j3Pi6zFwYQpXhhKbuFNWAc8urHuRp91+LIZ8t4Tv 1lJ2hOZES/Z4IWOqYIax/JpuO9C/2d/livPAJgPOQRToqykIworAE7IU5hU0M8Ihe1Jf svZ7ELl1g9ouvBe7nPulSIfbwlDXec3+KEfRszcISyIviDpETdJhh5mpYroX6Q4fOakY UTyA== X-Gm-Message-State: APjAAAU1w1J4+j57x8NOh4ZnCMybXwZTld1OcW4Ue0n5C8YAwdyZUkGB P1m5RIHvXDLAxiXIdxYMtxE= X-Google-Smtp-Source: APXvYqxCzOAfccd51g7qJ+E+tcZuFi8r8qK6qWwGhtWdR5CP7DtWiUNH49Ovcr4coAFqd27ZkNwJwg== X-Received: by 2002:a5d:6101:: with SMTP id v1mr42875577wrt.222.1556602190899; Mon, 29 Apr 2019 22:29:50 -0700 (PDT) Received: from localhost ([91.93.129.62]) by smtp.gmail.com with ESMTPSA id v17sm1138477wmc.30.2019.04.29.22.29.49 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 29 Apr 2019 22:29:49 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Tue, 30 Apr 2019 15:27:51 +0900 To: Petr Mladek Cc: Sergey Senozhatsky , Feng Tang , Andrew Morton , Steven Rostedt , Sergey Senozhatsky , linux-kernel@vger.kernel.org, Aaro Koskinen , Kees Cook , Borislav Petkov Subject: Re: [PATCH v4] panic: add an option to replay all the printk message in buffer Message-ID: <20190430062751.GA399@tigerII.localdomain> References: <1556199137-14163-1-git-send-email-feng.tang@intel.com> <20190426074934.seje2tn5p6fsuwaq@pathway.suse.cz> <20190426135316.GA505@tigerII.localdomain> <20190426141426.h7hpvhr3rqp7umbk@pathway.suse.cz> <20190426164302.GA26127@tigerII.localdomain> <20190426171640.GA7413@tigerII.localdomain> <20190429114423.yr7hbmfrfbravgsv@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190429114423.yr7hbmfrfbravgsv@pathway.suse.cz> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (04/29/19 13:44), Petr Mladek wrote: > On Sat 2019-04-27 02:16:40, Sergey Senozhatsky wrote: > > On (04/27/19 01:43), Sergey Senozhatsky wrote: > > [..] > > > > The console waiter logic is effective but it does not always > > > > work. The current console owner must be calling the console > > > > drivers. > > > > > > > > > Hmm, we might have a bit of a problem here, maybe. > > > > > > > > Hmm, the printk() might wait forever when NMI stopped > > > > the current console owner in the console driver code > > > > or with the logbuf_lock taken. > > > > > > I guess this is why we re-init logbuf lock from panic, > > > however, we don't do anything with the console_owner. > > > > > The console waiter logic might get solved by clearing > > > > the console_owner in console_flush_on_panic(). It can't > > > > be much worse, we already ignore console_lock() there, ... > > > > Hmm, or maybe we are fine... console_waiter logic should work > > before we send out stop IPI/NMI from panic CPU. When we call > > flush_on_panic() console_unlock() clears console_owner, so > > panic_print_sys_info() should not deadlock on console_owner. > > Good point! > > > It's probably only problematic if we kill a console_owner > > CPU and then try to printk() (from smp_send_stop()) before > > we do flush_on_panic()->console_unlock(). > > Yup. There are called several functions between smp_send_stop() > and console_flush_on_panic(). > > The question is if it is worth a code complication. We could > never 100% guarantee that printk() would work in panic(). > I more and more understand what Peter Zijlstra means > by the duct taping. Agreed. -ss