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=-17.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 C956BC433E0 for ; Fri, 22 Jan 2021 14:56:59 +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 37D0121D7A for ; Fri, 22 Jan 2021 14:56:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 37D0121D7A 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]:60920 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l2xru-0005dG-8b for qemu-devel@archiver.kernel.org; Fri, 22 Jan 2021 09:56:58 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:58164) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l2xr7-0004nB-Pj for qemu-devel@nongnu.org; Fri, 22 Jan 2021 09:56:10 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:26942) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l2xr1-0001iK-Lu for qemu-devel@nongnu.org; Fri, 22 Jan 2021 09:56:09 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611327361; 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=+jU8Yk3Uohzmi5bWsCsK/pW9Rsg8007eTKL8Aw5rse0=; b=VdIR6GlfkJrZTeK0H/9UaAGf+KOtXisS7h1SLD970v5A/H1IfvmPWYnrGLbTQj99x2hlqW KKbB2lhdEcukJ5qyFVsXCMAQS6errbvtpIz5Ru+HPoMtq/ing00pHE7xAOlvYQBQQxXNOq Kv/f/xscgPofOtr4B82tmgoRxOrAWsI= 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-261-fj8kBHECMCe5-zEOVzWcKA-1; Fri, 22 Jan 2021 09:55:59 -0500 X-MC-Unique: fj8kBHECMCe5-zEOVzWcKA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 57C90107ACE4 for ; Fri, 22 Jan 2021 14:55:58 +0000 (UTC) Received: from [10.3.113.116] (ovpn-113-116.phx2.redhat.com [10.3.113.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E611360BF3; Fri, 22 Jan 2021 14:55:54 +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> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <8480a6bf-f228-30c8-0083-d35f4dbe732b@redhat.com> Date: Fri, 22 Jan 2021 08:55:54 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210122102041.27031-1-mreitz@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@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: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.182, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.221, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=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 , =?UTF-8?B?TMOhc3psw7Mgw4lyc2Vr?= , Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 1/22/21 4:20 AM, Max Reitz wrote: > Modifying signal handlers is a process-global operation. When two > threads run coroutine-sigaltstack's qemu_coroutine_new() concurrently, > they may interfere with each other: One of them may revert the SIGUSR2 > handler back to the default between the other thread setting up > coroutine_trampoline() as the handler and raising SIGUSR2. That SIGUSR2 > will then lead to the process exiting. > > Outside of coroutine-sigaltstack, qemu does not use SIGUSR2. We can > thus keep the signal handler installed all the time. > CoroutineThreadState.tr_handler tells coroutine_trampoline() whether its > stack is set up so a new coroutine is to be launched (i.e., it should > invoke sigsetjmp()), or not (i.e., the signal came from an external > source and we should just perform the default action, which is to exit > the process). Not just exit the process, but exit due to a signal. It matters... > > Note that in user-mode emulation, the guest can register signal handlers > for any signal but SIGSEGV and SIGBUS, so if it registers a SIGUSR2 > handler, sigaltstack coroutines will break from then on. However, we do > not use coroutines for user-mode emulation, so that is fine. > > Suggested-by: Laszlo Ersek > Signed-off-by: Max Reitz > --- > util/coroutine-sigaltstack.c | 56 +++++++++++++++++++----------------- > 1 file changed, 29 insertions(+), 27 deletions(-) > > @@ -121,7 +138,17 @@ static void coroutine_trampoline(int signal) > /* Get the thread specific information */ > coTS = coroutine_get_thread_state(); > self = coTS->tr_handler; > + > + if (!self) { > + /* > + * This SIGUSR2 came from an external source, not from > + * qemu_coroutine_new(), so perform the default action. > + */ > + exit(0); > + } ...here. Silently exiting with status 0 is wrong; the correct response is to use signal(SIGUSR2, SIG_DFL); raise(SIGUSR2) to terminate the process in the same manner as if we had not installed our hander at all. With that fixed, Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org