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=-8.5 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS,USER_IN_DEF_DKIM_WL 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 37741C67839 for ; Wed, 12 Dec 2018 01:17:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DB30E2084E for ; Wed, 12 Dec 2018 01:17:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="OycJrGw2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB30E2084E Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.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 S1726270AbeLLBRD (ORCPT ); Tue, 11 Dec 2018 20:17:03 -0500 Received: from mail-io1-f65.google.com ([209.85.166.65]:35228 "EHLO mail-io1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726238AbeLLBRD (ORCPT ); Tue, 11 Dec 2018 20:17:03 -0500 Received: by mail-io1-f65.google.com with SMTP id i1so11487993ioo.2 for ; Tue, 11 Dec 2018 17:17:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=5ukqN8JMKVt9/LLOpVx1E5xGevrHb4jJC10yz52v72E=; b=OycJrGw2qxKjICAoQez/0yslurM6yGC2Ds1ns29fs/f3j0hCXAYqX3WjIjsEh6D20X Me0DOvyvDUqO90SMp7dMhj3EfqVfzBmv8+zF6QrUQHQANqOVSV9zmaKzcWzYRlH/LfFq j+e7tk1+FpDGOy3Tft5+6UbtfafOymGpq8MD/DY0EyM7sndA9vAuJd9y2HcSTA7JbfXf EEKU/8/yu/NfnmKAoGwL/dMdSYzYHD9m4tF/VFzY1vS58ikTTKoaL1Dj6XW1dpKzYd7O YgjwDHwG0OLzFaeJWl07vdpFLbpAX/FGgMf136sf/jGj+5TpsnFOCwlzVIyq3Lkg0KYk RQKg== 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=5ukqN8JMKVt9/LLOpVx1E5xGevrHb4jJC10yz52v72E=; b=pf3vdlScH79kKyto+Ac+BbyosQxEaj9oYnEH5DY2Ze1z8EqpLgzmJ1+v084wMRfD/O 5o1fC/jkz+cXGU/AUHwD+KK0BtJFO/tfOtZ0Ay5k1RnOw8FVPhJOI+3iFa8DPXbMhQlq K2sxoK9ni9UhBvcYj6oIc86T0iscNosmzK70N6GwoA4kc9i/0be2p+cRD0lBS93z4Zgt +Uz6fIJe1rEUl68bfYvsjGCs2N3VeMFzaqz65brd4zMkWU850qyuLsuHG2CFS1mciQ9q O6zwqZPJfO/T59JCZUENmPjSSW0Le7LonlY+sdztzicExT5HbUwhLzoEkdB8VEAUNZZ8 NiLw== X-Gm-Message-State: AA+aEWYfBlUyNlC4zP/SUwbgw0jbfmFvjD7sDOOMcUXIMhDteXa3yX1B jbm1eYxW4bIpScRGxaAPSTvMgH2/XwQxFq7DPPQVLg== X-Google-Smtp-Source: AFSGD/VO88ESmk2z+1fSpan/EjZSx1y1iP3PMTxC9hf0O5FJSehQ58tPIyxNrHMBWAqe7MOB+qfs9JvWLXNSSOmLsgE= X-Received: by 2002:a6b:e303:: with SMTP id u3mr15685387ioc.196.1544577421735; Tue, 11 Dec 2018 17:17:01 -0800 (PST) MIME-Version: 1.0 References: <20181003091400.rgdjpjeaoinnrysx@pathway.suse.cz> <20181003133704.43a58cf5@gandalf.local.home> <20181004074442.GA12879@jagdpanzerIV> <20181004083609.kcziz2ynwi2w7lcm@pathway.suse.cz> <20181004085515.GC12879@jagdpanzerIV> <20181022100952.GA1147@jagdpanzerIV> <20181109064740.GE599@jagdpanzerIV> In-Reply-To: <20181109064740.GE599@jagdpanzerIV> From: Daniel Wang Date: Tue, 11 Dec 2018 17:16:49 -0800 Message-ID: Subject: Re: 4.14 backport request for dbdda842fe96f: "printk: Add console owner and waiter logic to load balance console writes" To: Sergey Senozhatsky Cc: Petr Mladek , Steven Rostedt , stable@vger.kernel.org, Alexander.Levin@microsoft.com, Andrew Morton , byungchul.park@lge.com, dave.hansen@intel.com, hannes@cmpxchg.org, jack@suse.cz, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mathieu Desnoyers , Mel Gorman , mhocko@kernel.org, pavel@ucw.cz, penguin-kernel@i-love.sakura.ne.jp, Peter Zijlstra , tj@kernel.org, Linus Torvalds , vbabka@suse.cz, Cong Wang , Peter Feiner Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="00000000000093b530057cc8f429" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --00000000000093b530057cc8f429 Content-Type: text/plain; charset="UTF-8" > Let's first figure out if it works. I would still like to try applying your patches that went into printk.git, but for now I wonder if we can get Steven's patch into 4.14 first, for at least we know it mitigated the issue if not fundamentally addressed it, and we've agreed it's an innocuous change that doesn't risk breaking stable. I haven't done this before so I'll need your help. What's the next step to actually get Steven's patch *in* linux-4.14.y? According to https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html I am supposed to send an email with the patch ID and subject, which are both mentioned in this email. Should I send another one? What's the process like? Thanks! On Thu, Nov 8, 2018 at 10:47 PM Sergey Senozhatsky wrote: > > On (11/01/18 09:05), Daniel Wang wrote: > > > Another deadlock scenario could be the following one: > > > > > > printk() > > > console_trylock() > > > down_trylock() > > > raw_spin_lock_irqsave(&sem->lock, flags) > > > > > > panic() > > > console_flush_on_panic() > > > console_trylock() > > > raw_spin_lock_irqsave(&sem->lock, flags) // deadlock > > > > > > There are no patches addressing this one at the moment. And it's > > > unclear if you are hitting this scenario. > > > > I am not sure, but Steven's patches did make the deadlock I saw go away... > > You certainly can find cases when "busy spin on console_sem owner" logic > can reduce some possibilities. > > But spin_lock(&lock); NMI; spin_lock(&lock); code is still in the kernel. > > > A little swamped by other things lately but I'll run a test with it. > > If it works, would you recommend taking your patch alone > > Let's first figure out if it works. > > -ss -- Best, Daniel On Thu, Nov 8, 2018 at 10:47 PM Sergey Senozhatsky wrote: > > On (11/01/18 09:05), Daniel Wang wrote: > > > Another deadlock scenario could be the following one: > > > > > > printk() > > > console_trylock() > > > down_trylock() > > > raw_spin_lock_irqsave(&sem->lock, flags) > > > > > > panic() > > > console_flush_on_panic() > > > console_trylock() > > > raw_spin_lock_irqsave(&sem->lock, flags) // deadlock > > > > > > There are no patches addressing this one at the moment. And it's > > > unclear if you are hitting this scenario. > > > > I am not sure, but Steven's patches did make the deadlock I saw go away... > > You certainly can find cases when "busy spin on console_sem owner" logic > can reduce some possibilities. > > But spin_lock(&lock); NMI; spin_lock(&lock); code is still in the kernel. > > > A little swamped by other things lately but I'll run a test with it. > > If it works, would you recommend taking your patch alone > > Let's first figure out if it works. > > -ss -- Best, Daniel --00000000000093b530057cc8f429 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIIS7QYJKoZIhvcNAQcCoIIS3jCCEtoCAQExDzANBglghkgBZQMEAgEFADALBgkqhkiG9w0BBwGg ghBTMIIEXDCCA0SgAwIBAgIOSBtqDm4P/739RPqw/wcwDQYJKoZIhvcNAQELBQAwZDELMAkGA1UE BhMCQkUxGTAXBgNVBAoTEEdsb2JhbFNpZ24gbnYtc2ExOjA4BgNVBAMTMUdsb2JhbFNpZ24gUGVy 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