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=-0.8 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 5463CC433E0 for ; Sat, 4 Jul 2020 11:37:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2E08C2084C for ; Sat, 4 Jul 2020 11:37:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="o7q7SjXm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727906AbgGDLhb (ORCPT ); Sat, 4 Jul 2020 07:37:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40092 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726621AbgGDLhb (ORCPT ); Sat, 4 Jul 2020 07:37:31 -0400 Received: from mail-pj1-x1043.google.com (mail-pj1-x1043.google.com [IPv6:2607:f8b0:4864:20::1043]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 48AE7C061794 for ; Sat, 4 Jul 2020 04:37:31 -0700 (PDT) Received: by mail-pj1-x1043.google.com with SMTP id cm21so5530266pjb.3 for ; Sat, 04 Jul 2020 04:37:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=4plqkhvVW/dHuIMMbhq1LQlta+pdw76VHrKkcf+m5iQ=; b=o7q7SjXmYnY30eDj0Sa+Ilrh7Nbozwd343h6x09nNYV6HKAPXg5MLJ0YSzSKtG4laz lSOAZJ62klEIMeDTY1m80EXHJp2NBqyvadia3ut9igvApRfwDgN10JOCBEKQYGY7GnjO 6tvFsI+YUxPCZGjS0/rmAJohvDoyuQQAT+RXEvh9Fdj6zFlMOeQGojpMMRYYQCBcwkPa 055NYk2wCcA3BwJRjCWg1sW/wRNIrW6a31NPaS1Obpwx5TNLZTOJMNsfni9IrBrUbdAw mIYVztcCi+e53ph9SnZGE3nDCEdbCJQ46El82W48EQasgmKVxbwMD7Avmzio68xvtF+j KTqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=4plqkhvVW/dHuIMMbhq1LQlta+pdw76VHrKkcf+m5iQ=; b=tktK/DPr46mWz8M2eJSS9AAFbtZKq4ZdqAgtDCsWahYxDN5T5urxzMxcxLZkLO3MEf lA6jeLotim8lITpEkrDST4cK5++18LfoGiTMWnhIUa3J00fdi967yYjqdbw4Zu+NwNxD 7YQeIL7TuAyLOWTOadxtveFzO/wB+GFmuqXBdb0TBBG92QABRRRdBzq1RCbaoC6qxpMT G+Ff7eeH59BkRx8R0LIKBTjxkpnHkNRriqVXxoOR/xVcqpPqtYmyUYEaB72Y38zSY7+f tbZm7VITU8ohrnAqkxsZ9nIk616DtR0XbSVusj4T2yy0OJ/RttuJlCJ6JXdkYPJ31TBe KRzg== X-Gm-Message-State: AOAM533lc0tUEO6sNwpkLVabqGmWE0KRuwxDE/N9iXfWjSzRQCO7cTsD d8V6dcbOd5rt9U3+Tbj9OWNmGmteAwAmHa7YF+Q= X-Google-Smtp-Source: ABdhPJwyL6hejhdOKtLk/8BNlcTJZtRGhcJrJxoAS5Tf95pbjgX8rcextWE547S3/0FtbsgkGF5z2RrY+5rxYa5DJv4= X-Received: by 2002:a17:90b:3547:: with SMTP id lt7mr16736902pjb.181.1593862650846; Sat, 04 Jul 2020 04:37:30 -0700 (PDT) MIME-Version: 1.0 References: <20200630035816.GA21591@jagdpanzerIV.localdomain> <20200630102141.GA11587@alley> <20200630105512.GA530@jagdpanzerIV.localdomain> <20200630122239.GD6173@alley> <20200630130534.GB145027@jagdpanzerIV.localdomain> <20200630180255.GD37466@atomide.com> <20200702051213.GB3450@jagdpanzerIV.localdomain> <20200702054033.GC3450@jagdpanzerIV.localdomain> <20200702082008.GE3703480@smile.fi.intel.com> <20200703105302.GC182102@jagdpanzerIV.localdomain> In-Reply-To: <20200703105302.GC182102@jagdpanzerIV.localdomain> From: Andy Shevchenko Date: Sat, 4 Jul 2020 14:37:14 +0300 Message-ID: Subject: Re: UART/TTY console deadlock To: Sergey Senozhatsky , Andy Shevchenko Cc: Tony Lindgren , Petr Mladek , Raul Rangel , Sergey Senozhatsky , linux-kernel , Greg Kroah-Hartman , kurt@linutronix.de, "S, Shirish" , Peter Zijlstra , John Ogness , Steven Rostedt Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 3, 2020 at 1:53 PM Sergey Senozhatsky wrote: > > On (20/07/02 11:20), Andy Shevchenko wrote: > > > > I didn't look into this deeply, but my understanding that this is something for > > special case when you have several UART ports sharing the IRQ (multi-port card) > > and IRQ even maybe undesirable b/c it will confuse real IRQ handler. I don't > > remember details, but AFAIR IRQ handler does a busyloop to service as much as > > possible and in between it may release the lock (again, multi-port UART cards), > > that's why we better avoid IRQ event in the first place. > > But it's my pure speculation. > > Hmm. Would different IRQ handlers use different UART port structures? ->irq > might be the only thing they share. Even if they use the same port, we > keep IRQs disabled on local CPU, and UART port locked. To unlock the UART > port during IRQ, the handler (on another CPU) first needs to acquire the > port->lock, which is locked by serial8250_do_startup(). It appears to be a RT kernel related. Don't know the state of affairs in RT nowadays, but maybe still relevant. See the commit 768aec0b5bcc ("serial: 8250: fix shared interrupts issues with SMP and RT kernels"). -- With Best Regards, Andy Shevchenko