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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A453C433EF for ; Fri, 10 Jun 2022 15:35:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344912AbiFJPfF (ORCPT ); Fri, 10 Jun 2022 11:35:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32858 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238346AbiFJPfD (ORCPT ); Fri, 10 Jun 2022 11:35:03 -0400 Received: from mail-yb1-xb30.google.com (mail-yb1-xb30.google.com [IPv6:2607:f8b0:4864:20::b30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 148CB1CF178 for ; Fri, 10 Jun 2022 08:35:02 -0700 (PDT) Received: by mail-yb1-xb30.google.com with SMTP id h27so3384989ybj.4 for ; Fri, 10 Jun 2022 08:35:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=C14q5Dy6Du+XHvgXj/VVrOd11AGI0NT/UdqNE8EdfT4=; b=Knbu7UAyfQ9/FBzc3DL1apaZSuXrKn83d3MtaAVYfYl0no7peCglt6G2ZzMZzV67dq AA705/VF7SMPxEnDOG07G247GA9eif2QHe43vSOQB1WDZM29CSIiPIFG0nObuGBWL/5g 9cDIjOpqkH90hUqh1OPfGQ2eP3S5DtxFURji18+qpMr8BIqqxYmECZha+3/OaY+a4Go4 /DLQa1gi83e5YJcJm5gQ4ma5kN6cLPnycMHXGfXtcZ217Hj5Dhz4Pzhwl9+f4yhlg63Z dvGUNmc+7vuWipq28hCch+cpXZN7rRF4m0TO+KQ6QBU27ft2JjUB5CNtaLp1JGx3BsBL LsJg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=C14q5Dy6Du+XHvgXj/VVrOd11AGI0NT/UdqNE8EdfT4=; b=hqlzhZdao9A7F5LCB4rJOIVkQmReO1KLL6cqEhGfIwmCcaJHhVSF3qaeqUpGFtGaTt jqYxhcbVobds6+BIbifVDXga/9HXCimCaURQs1PRyI/5mE2mVH6vhCrrn/BBxt5CsnXm 8hm28wJmMim5U6gAs2Hta95JmsW1u9CfGZZASSE3AiX0uCq/Dx7+gPKaTNF0DOqFfqNu NAfEzP8PNVfM07WYwYYR75+XiybjwultnZWHDZzw3CIngDaKc8OEw/QzOk2yvOG13lET cG073gwl6DPGglYoNtwhnqvuofzCc2fKwpyMXQfXQ944zUxAZBc83XudzWMs1y9UxQZx KElA== X-Gm-Message-State: AOAM530tJLHpwUSClrUudQr7kA+EKVZkuuWiT5VBLgDBMXyqPVf5pWSo rUBrM0m0lt+vslDaQxVeZ8lGZHyXoM8tmyR03Cg= X-Google-Smtp-Source: ABdhPJyE0wTeNeQSFfZWpdVduVIqNiDJ6Db1s47ilpLanpPzyafdxrAH+yvrGRlISWMDLXFqBCaW6UEvu/qHPAhZKxk= X-Received: by 2002:a25:d195:0:b0:663:ff7a:b5bc with SMTP id i143-20020a25d195000000b00663ff7ab5bcmr13226171ybg.51.1654875301266; Fri, 10 Jun 2022 08:35:01 -0700 (PDT) MIME-Version: 1.0 References: <87y1y48spg.fsf@jogness.linutronix.de> In-Reply-To: <87y1y48spg.fsf@jogness.linutronix.de> From: Peter Geis Date: Fri, 10 Jun 2022 11:34:47 -0400 Message-ID: Subject: Re: [BUG] Threaded printk breaks early debugging To: John Ogness Cc: Petr Mladek , Sergey Senozhatsky , Linux Kernel Mailing List , "open list:ARM/Rockchip SoC..." Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 10, 2022 at 11:05 AM John Ogness wrote: > > Hi Peter, > > On 2022-06-10, Peter Geis wrote: > > However I've run into an issue debugging early boot issues. Anything > > that causes the kernel threading system to die (for example here, a > > NPE) causes the boot console to halt before it outputs the error. > > A null pointer exception should trigger a panic, which will cause printk > to enter direct mode for the oops. It should be just as effective as > before introducing the printing kthreads. This might be a side effect of the fact that this is on a low powered arm64 board. I noticed with threading enabled during large bursts the console drops an excessive amount of messages. It's especially apparent during the handover from earlycon to the normal console. > > Can you please provide a test case or patch that will trigger the > problem you refer to? Unfortunately no, unless you have a Rockchip rk356x device with both DSI and HDMI. We're working on adding DSI support to the new video output driver, and when both are enabled it tosses a NPE. > > > Would it be possible to have both a kconfig option and a runtime > > option to toggle printk_fallback_preferred_direct()? Currently I've > > had to force it at all times while debugging. > > It would be trivial to provide a boot parameter for this behavior, but I > think we first need to see a real problem and also see if we can fix > that problem. > > John Ogness