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=-1.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 AFA79C282E1 for ; Mon, 22 Apr 2019 16:51:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 80333214AE for ; Mon, 22 Apr 2019 16:51:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="HARsNYU4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728003AbfDVQvA (ORCPT ); Mon, 22 Apr 2019 12:51:00 -0400 Received: from mail-it1-f170.google.com ([209.85.166.170]:51711 "EHLO mail-it1-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727378AbfDVQu7 (ORCPT ); Mon, 22 Apr 2019 12:50:59 -0400 Received: by mail-it1-f170.google.com with SMTP id s3so18797033itk.1 for ; Mon, 22 Apr 2019 09:50:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=k2dbBBh9t0iowJHslezHA4ZI/3Wpcgqn3HcJk4izQPg=; b=HARsNYU4REyrMUOR63OaCVeXUc4X+T6Cg+FPYkZKajRxHBjNiCnepMzS1MpLGG+SGY kkRDJV8AP2z3txhL4VIBfdglXiH2GWO/P5GQQhvEqCK/oBxL1owsNA26bJrP4z+xgkV+ Kd7suDz7lP76CmaNgm+IqTt52MLiRq9mUJbrQpfStE1WwLNMkhA1rldnnMA7KPvCRWAW 85qAbeeKCS76BZHHE5KgYHeRJRwHYwPF7+bxes6qcPl888f4QMdbVEQsVlW2YB/Q4ans aYye7O9f+kqPLLKwzS4TXf3ZlRHBtfSBKIh1kXg2RFrYNabcjjqc7IN4w2HdCd5h6aI+ obHw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=k2dbBBh9t0iowJHslezHA4ZI/3Wpcgqn3HcJk4izQPg=; b=s8//k/8WdyjOmorSUOzp4E8bPn7Yd1h5TflqW5gzfEdO5CnQ2lXrSDrIKL8O4TKxYg bd2MCx4lo8lzgkbUggInYNyBR4CeRPUQcms0lW0s6txGlyIBoC39XvRbiF2SrjOfCCDM +3Qle/PJ7kvRDZQ4kfPVWtzjMDAl1OBXbHG05dAb6/NdCh7fBz7cZjd3i5C9nTu1+OJz h9T1mWE8MiQm2jNh1Kz0tUKmVfAoIU+VYOWe1XCI4iD2eTqL2vvy/+KChbMRnrvT9GRc 5/xWKapfsFnw1J2shVi8a5cIplGelYJkix6hk8LhRHv/qt821f+qwNY3H9zenQOkmR5C tYTQ== X-Gm-Message-State: APjAAAUYKWoJSH91wJPSNeEx/P4OIIQbERa4wjGgYPzoQc1KtE5xdGyq 4r892VaMOvglP4thaTklaze27A== X-Google-Smtp-Source: APXvYqyP1Axp3Ers5w70J7EzBKP3oGOF47aDrFAk4nmvE4iXG42mrgYyIcLa12prNynFIV6/wfzvCg== X-Received: by 2002:a24:ac45:: with SMTP id m5mr6373117iti.28.1555951858965; Mon, 22 Apr 2019 09:50:58 -0700 (PDT) Received: from [192.168.1.158] ([216.160.245.98]) by smtp.gmail.com with ESMTPSA id p67sm6428046itb.11.2019.04.22.09.50.57 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 22 Apr 2019 09:50:58 -0700 (PDT) Subject: Re: WARNING in percpu_ref_kill_and_confirm To: Linus Torvalds Cc: syzbot , Arnd Bergmann , Borislav Petkov , "Darrick J. Wong" , Greg Kroah-Hartman , Peter Anvin , Linux API , linux-arch , linux-block , linux-fsdevel , Linux List Kernel Mailing , Andrew Lutomirski , Mathieu Desnoyers , Ingo Molnar , Michael Ellerman , syzkaller-bugs , Thomas Gleixner , Al Viro , the arch/x86 maintainers References: <00000000000043fe9c058720a5d3@google.com> <53a17444-9539-5810-82a0-ceeefa742508@kernel.dk> From: Jens Axboe Message-ID: <4179bb56-0285-9e14-5ae9-7a16957b6210@kernel.dk> Date: Mon, 22 Apr 2019 10:50:56 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/22/19 10:48 AM, Linus Torvalds wrote: > On Mon, Apr 22, 2019 at 9:38 AM Jens Axboe wrote: >> >> With the mutex change in, I can trigger it in a second or so. Just ran >> the reproducer with that change reverted, and I'm not seeing any badness. >> So I do wonder if the bisect results are accurate? > > Looking at the syzbot report, it's syzbot being confused. > > The actual WARNING in percpu_ref_kill_and_confirm() only happens with > recent kernels. > > But then syzbot mixes it up with a completely different bug: > > crash: BUG: MAX_STACK_TRACE_ENTRIES too low! > BUG: MAX_STACK_TRACE_ENTRIES too low! > > and for some reason decides that *that* bug is the same thing entirely. > > So yeah, I think the simple percpu_ref_is_dying() check is sufficient, > and that the syzbot bisection is completely bogus. Ah good, that makes me feel better. I'll queue the fix up, thanks. -- Jens Axboe