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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 7FF84C433DB for ; Mon, 25 Jan 2021 21:17:52 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 0F04120679 for ; Mon, 25 Jan 2021 21:17:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F04120679 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45760 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l49F9-0008KH-0N for qemu-devel@archiver.kernel.org; Mon, 25 Jan 2021 16:17:51 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:43012) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l49Dz-0007ft-JL for qemu-devel@nongnu.org; Mon, 25 Jan 2021 16:16:40 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:45552) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l49Dx-0000SJ-Ev for qemu-devel@nongnu.org; Mon, 25 Jan 2021 16:16:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611609395; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WU/RZqBKDjKgz1SwSlevNcuaVcDiYqz1mtFCR5Ifzhg=; b=DwTiI47CsTsuqxWwtSnBp3+7e+cCxfPFalhXeIU0w46Kk6aKa1qahMzs4LBlsYe6uB8rkz 5f//yJUrqDQ4HDi/U9QqI7up/qkdfqlUc+3Xg2+kiUQtLsI9q7gqaTcIwAyYbMCFEDAyL+ J3Di42KXLC3RScYY1S32MZaYvTO1+RA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-538-MYL0X6NROu-kyLu3lypPMg-1; Mon, 25 Jan 2021 16:16:33 -0500 X-MC-Unique: MYL0X6NROu-kyLu3lypPMg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 66B851007463; Mon, 25 Jan 2021 21:16:32 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-112-67.ams2.redhat.com [10.36.112.67]) by smtp.corp.redhat.com (Postfix) with ESMTP id DA02E60938; Mon, 25 Jan 2021 21:16:26 +0000 (UTC) Subject: Re: [PATCH] coroutine-sigaltstack: Keep SIGUSR2 handler up To: Max Reitz , qemu-devel@nongnu.org References: <20210122102041.27031-1-mreitz@redhat.com> <1121a803-98e7-6d41-119c-3d82717976ec@redhat.com> <95b1fd67-e980-be70-addc-6f1ac5f95f3d@redhat.com> <3cfa7f82-866b-e8b7-3e61-bb3dedff3226@redhat.com> From: Laszlo Ersek Message-ID: <1bf1290d-cd19-dd9e-5ce4-a4ceca0c04e1@redhat.com> Date: Mon, 25 Jan 2021 22:16:25 +0100 MIME-Version: 1.0 In-Reply-To: <3cfa7f82-866b-e8b7-3e61-bb3dedff3226@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=lersek@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=lersek@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.255, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Peter Maydell , "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" , Markus Armbruster , Stefan Hajnoczi , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 01/25/21 11:57, Max Reitz wrote: > On 23.01.21 01:41, Laszlo Ersek wrote: >> On 01/22/21 22:26, Laszlo Ersek wrote: >> >>> I'm drifting towards an overhaul of coroutine-sigaltstack, based on my >>> personal understanding of POSIX, but given that I can absolutely not >>> *test* coroutine-sigaltstack on the platforms where it actually matters, >>> an "overhaul" by me would be reckless. >>> >>> I didn't expect these skeletons when I first read Max's "Thread safety >>> of coroutine-sigaltstack" email :/ >>> >>> Max, after having worked on top of your patch for a few hours, I >>> officially endorse your mutex approach. I can't encourage you or myself >>> to touch this code, in good conscience. It's not that it's "bad"; it's >>> inexplicable and (to me) untestable. > > On one hand, that’s too bad; on the other perhaps it’s just for the > better to get all of this out of our minds again (for now)... O:) > >> I'm attaching a patch (based on 0e3246263068). I'm not convinced that I >> should take responsibility for this, given the lack of testability on my >> end. So I'm not posting it stand-alone even as an RFC. I've built it and >> have booted one of my existent domains with it, but that's all. > > FWIW, it looks good to me.  We should keep it in mind if in the future > for some reason sigaltstack becomes more important, but for now I’m not > too sad to abort any improvement efforts. OK -- so do you plan to post your mutex approach stand-alone? (Sorry if that's already been done and I've missed it.) I actually feel somewhat safe regarding my patch, as long as it is *only* executed on Linux hosts, and on other hosts that claim conformance to POSIX. But, of course, this whole thing has come up because of OSX... and I don't have the first clue about OSX. (For example whether sigsuspend() on OSX is prone to a spurious wakeup in response to SIGCONT.) Thanks Laszlo