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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 E1A65C433DF for ; Tue, 30 Jun 2020 13:05:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BCE4420672 for ; Tue, 30 Jun 2020 13:05:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Y91it/l5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729213AbgF3NFi (ORCPT ); Tue, 30 Jun 2020 09:05:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727850AbgF3NFi (ORCPT ); Tue, 30 Jun 2020 09:05:38 -0400 Received: from mail-pf1-x443.google.com (mail-pf1-x443.google.com [IPv6:2607:f8b0:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D3382C061755 for ; Tue, 30 Jun 2020 06:05:37 -0700 (PDT) Received: by mail-pf1-x443.google.com with SMTP id u5so9409505pfn.7 for ; Tue, 30 Jun 2020 06:05:37 -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; bh=mufd44kK17qFivOfQ57M8zO5lo5YkRfS0CDXZTF/ywg=; b=Y91it/l5NbOcjxp6l9p+t29xIg4Tr1A4sNjey1SCcwUtHu4K5Ip0GvSYTKocHTzNWI EKsyEfhc2vr1taxgHJmezL3HP/PsWyGAs/T+3gYGjezMw1eXltgErcOif2Li8aagFq0k bZctCh4NbPG8e8tIlKLmwtd7/9gzPnXsOD8OWc6oVb6KFUA3cEjDBsttXeYH8NhgNPcC Try4E8d9eRZ7aiTO7MfUa9GodFFpS5daq7F1cUJskO2sNf1B2iXPLIqsm6Ny7uV8CCjn VHn89cBVT7Ie3FFFUHkKqfqIIwMN5OMFHJ4wiVzQ/sevaZCtSlXh6mYlliv/qxKODLmn YFzg== 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; bh=mufd44kK17qFivOfQ57M8zO5lo5YkRfS0CDXZTF/ywg=; b=MXlGhHlU9BD/m2CRgQoQGiRXON5zpImG/LuO0Q6dlI3FmsXPPC585oQ1vQ1uddPD45 oS5gw06ou6/s5ZLqxLM1S/2dIdYmkn04mRX70dP9w4+4T/OVTutv8AWQIDD1BT3yCbjh er2MW2MfcAMF/20RKROTBcgLeEbjvLvmGNepmrO9SGjGOrljYPaQEQQU/vojgTx6QypT xBdJjoeq5v2lN3kkSupYd/hx6F+F3w3iUPXSoxQuHEGHxywK3/QcOQ+kEwniT7acqTlt vgDznuCnwQEY0RQl2kFIWZy3RtAatARm1bgefTXLbo5PxBOo4z5NAVusy8ekD9IrZAi3 T7Sg== X-Gm-Message-State: AOAM531W5aZX5aclSpHfyXaRt9PYys7+gGFyVDgAkKrzw/hUyLXrjBvk xaQIcUJcC9zfh2PqFrcRDn7DWHKi X-Google-Smtp-Source: ABdhPJxApFM9BscCEAXQNohFw+pXxYJ4pBBTEK0Y976nJbzWLlZ+LRBEDAb34eKuypdsF/L8XdodtQ== X-Received: by 2002:a63:db46:: with SMTP id x6mr12336774pgi.265.1593522337263; Tue, 30 Jun 2020 06:05:37 -0700 (PDT) Received: from localhost ([2409:10:2e40:5100:6e29:95ff:fe2d:8f34]) by smtp.gmail.com with ESMTPSA id a3sm2668732pgd.73.2020.06.30.06.05.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Jun 2020 06:05:36 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Tue, 30 Jun 2020 22:05:34 +0900 To: Petr Mladek Cc: Sergey Senozhatsky , Andy Shevchenko , Raul Rangel , Tony Lindgren , Sergey Senozhatsky , linux-kernel , Greg Kroah-Hartman , Andy Shevchenko , kurt@linutronix.de, "S, Shirish" , Peter Zijlstra , John Ogness , Steven Rostedt Subject: Re: UART/TTY console deadlock Message-ID: <20200630130534.GB145027@jagdpanzerIV.localdomain> References: <20200630035816.GA21591@jagdpanzerIV.localdomain> <20200630102141.GA11587@alley> <20200630105512.GA530@jagdpanzerIV.localdomain> <20200630122239.GD6173@alley> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200630122239.GD6173@alley> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (20/06/30 14:22), Petr Mladek wrote: > On Tue 2020-06-30 19:55:12, Sergey Senozhatsky wrote: > > On (20/06/30 12:21), Petr Mladek wrote: > > > Anyway, I believe that this is a false positive. If I get it correctly > > > serial8250_do_startup() must be called before the serial port could > > > be registered as a console. It means that it could not be called > > > from inside printk(). > > > > >From my understanding, I'm afraid we are talking about actual deadlock > > here, not about false positive report. Quoting the original email: > > IMHO, it is not clear. > Yea. Maybe it is, maybe it's not. Regardless, after lockdep tells us there is something it doesn't like, it disables itself, so false positives render lockdep useless. > > > > @@ -2275,6 +2275,11 @@ int serial8250_do_startup(struct uart_port *port) > > > > > > > > if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) { > > > > unsigned char iir1; > > > > + bool irq_shared = up->port.irqflags & IRQF_SHARED; > > > > + > > > > + if (irq_shared) > > > > + disable_irq_nosync(port->irq); > > > > + > > > > /* > > > > * Test for UARTs that do not reassert THRE when the > > > > * transmitter is idle and the interrupt has already > > > > @@ -2284,8 +2289,6 @@ int serial8250_do_startup(struct uart_port *port) > > > > * allow register changes to become visible. > > > > */ > > > > spin_lock_irqsave(&port->lock, flags); > > > > - if (up->port.irqflags & IRQF_SHARED) > > > > - disable_irq_nosync(port->irq); > > > > > > > > wait_for_xmitr(up, UART_LSR_THRE); > > > > serial_port_out_sync(port, UART_IER, UART_IER_THRI); > > > > @@ -2297,9 +2300,9 @@ int serial8250_do_startup(struct uart_port *port) > > > > iir = serial_port_in(port, UART_IIR); > > > > serial_port_out(port, UART_IER, 0); > > > > > > > > - if (port->irqflags & IRQF_SHARED) > > > > - enable_irq(port->irq); > > > > spin_unlock_irqrestore(&port->lock, flags); > > > > + if (irq_shared) > > > > + enable_irq(port->irq); > > > > > > > > /* > > > > * If the interrupt is not reasserted, or we otherwise > > > > > > I think that it might be safe but I am not 100% sure, sigh. > > > > Yeah, I'm not 100%, but I'd give it a try. > > I do not feel brave enough to ack it today. But I am all for trying it > if anyone more familiar with the code is fine with it. I see. Well, I suppose we need Ack-s from tty/serial/8250 maintainers. I would not be very happy if _only_ printk people Ack the patch. -ss