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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 A48CEC4338F for ; Wed, 28 Jul 2021 12:53:33 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8652560E09 for ; Wed, 28 Jul 2021 12:53:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 8652560E09 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=molgen.mpg.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4GZYVy4Kg8z3bWM for ; Wed, 28 Jul 2021 22:53:30 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=molgen.mpg.de (client-ip=141.14.17.11; helo=mx1.molgen.mpg.de; envelope-from=pmenzel@molgen.mpg.de; receiver=) Received: from mx1.molgen.mpg.de (mx3.molgen.mpg.de [141.14.17.11]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4GZYVZ0ZD3z2yhd for ; Wed, 28 Jul 2021 22:53:07 +1000 (AEST) Received: from [141.14.220.45] (g45.guest.molgen.mpg.de [141.14.220.45]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: pmenzel) by mx.molgen.mpg.de (Postfix) with ESMTPSA id 339F161E5FE00; Wed, 28 Jul 2021 14:53:01 +0200 (CEST) Subject: Re: Possible regression by ab037dd87a2f (powerpc/vdso: Switch VDSO to generic C implementation.) To: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Christophe Leroy References: <3661999754da1a5e5c810fa669654cc7db95b059.camel@kernel.crashing.org> <4f037af0-5066-ebb9-53a6-733b3bd8eeac@molgen.mpg.de> <878s1q1udj.fsf@mpe.ellerman.id.au> From: Paul Menzel Message-ID: Date: Wed, 28 Jul 2021 14:53:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <878s1q1udj.fsf@mpe.ellerman.id.au> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Derek Parker , Dmitrii Okunev , murp@ibm.com, linuxppc-dev@lists.ozlabs.org, laboger@linux.vnet.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Dear Michael, Am 28.07.21 um 14:43 schrieb Michael Ellerman: > Paul Menzel writes: >> Am 28.07.21 um 01:14 schrieb Benjamin Herrenschmidt: >>> On Tue, 2021-07-27 at 10:45 +0200, Paul Menzel wrote: >> >>>> On ppc64le Go 1.16.2 from Ubuntu 21.04 terminates with a segmentation >>>> fault [1], and it might be related to *[release-branch.go1.16] runtime: >>>> fix crash during VDSO calls on PowerPC* [2], conjecturing that commit >>>> ab037dd87a2f (powerpc/vdso: Switch VDSO to generic C implementation.) >>>> added in Linux 5.11 causes this. >>>> >>>> If this is indeed the case, this would be a regression in userspace. Is >>>> there a generic fix or should the change be reverted? >>> >>> From the look at the links you posted, this appears to be completely >>> broken assumptions by Go that some registers don't change while calling >>> what essentially are external library functions *while inside those >>> functions* (ie in this case from a signal handler). >>> >>> I suppose it would be possible to build the VDSO with gcc arguments to >>> make it not use r30, but that's just gross... >> >> Thank you for looking into this. No idea, if it falls under Linux’ no >> regression policy or not. > > Reluctantly yes, I think it does. Though it would have been good if it > had been reported to us sooner. > > It looks like that Go fix is only committed to master, and neither of > the latest Go 1.16 or 1.15 releases contain the fix? ie. there's no way > for a user to get a working version of Go other than building master? I heard it is going to be in Go 1.16.7, but I do not know much about Go. Maybe the folks in Cc can chime in. > I'll see if we can work around it in the kernel. Are you able to test a > kernel patch if I send you one? Yes, I could test a Linux kernel patch on ppc64le (POWER 8) running Ubuntu 21.04. Kind regards, Paul