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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 2D68EC54FB9 for ; Thu, 16 Nov 2023 11:22:27 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r3aRn-0007uD-IO; Thu, 16 Nov 2023 06:22:11 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r3aRm-0007ty-Ix for qemu-devel@nongnu.org; Thu, 16 Nov 2023 06:22:10 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r3aRY-00027G-OY for qemu-devel@nongnu.org; Thu, 16 Nov 2023 06:22:10 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1700133715; h=from:from:reply-to: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=T1gaQnwmhiIvqwheRag9lppivBOQBPv9o6ksKSqZSeU=; b=DhTREGDsn+jLyHA7+WRa+Pa0Bvb2GcULOCm56Gp/cjTxc8zcGvteSlQQZuYQ1dtS16hLWw lJbDhHVXzO5apJH/Rt2IKL9Qm3VgFax5isVoe8emN4plYywGvdtC+Z+OYw2hY63iieLkvc yZLCvB84ivkA4O3AFz/5XR2jfge4YMg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-653-ArdN8kGlPL2zfQPnC-ix3A-1; Thu, 16 Nov 2023 06:21:52 -0500 X-MC-Unique: ArdN8kGlPL2zfQPnC-ix3A-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 55410185A782; Thu, 16 Nov 2023 11:21:52 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.34]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 15EDE1C060AE; Thu, 16 Nov 2023 11:21:50 +0000 (UTC) Date: Thu, 16 Nov 2023 11:21:48 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Steven Sistare Cc: qemu-devel@nongnu.org, Markus Armbruster , Michael Roth , "Dr. David Alan Gilbert" Subject: Re: [PATCH] monitor: flush messages on abort Message-ID: References: <1699027289-213995-1-git-send-email-steven.sistare@oracle.com> <3d45ebc0-de9f-4051-9c08-47e40fea65da@oracle.com> <587d8444-17a4-4d19-a856-ac55e46069c5@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <587d8444-17a4-4d19-a856-ac55e46069c5@oracle.com> User-Agent: Mutt/2.2.10 (2023-03-25) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.099, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Nov 15, 2023 at 10:30:29AM -0500, Steven Sistare wrote: > > > On 11/6/2023 5:10 AM, Daniel P. Berrangé wrote: > > On Fri, Nov 03, 2023 at 03:51:00PM -0400, Steven Sistare wrote: > >> On 11/3/2023 1:33 PM, Daniel P. Berrangé wrote: > >>> On Fri, Nov 03, 2023 at 09:01:29AM -0700, Steve Sistare wrote: > >>>> Buffered monitor output is lost when abort() is called. The pattern > >>>> error_report() followed by abort() occurs about 60 times, so valuable > >>>> information is being lost when the abort is called in the context of a > >>>> monitor command. > >>> > >>> I'm curious, was there a particular abort() scenario that you hit ? > >> > >> Yes, while tweaking the suspended state, and forgetting to add transitions: > >> > >> error_report("invalid runstate transition: '%s' -> '%s'", > >> abort(); > >> > >> But I have previously hit this for other errors. > >> > >>> For some crude statistics: > >>> > >>> $ for i in abort return exit goto ; do echo -n "$i: " ; git grep --after 1 error_report | grep $i | wc -l ; done > >>> abort: 47 > >>> return: 512 > >>> exit: 458 > >>> goto: 177 > >>> > >>> to me those numbers say that calling "abort()" after error_report > >>> should be considered a bug, and we can blanket replace all the > >>> abort() calls with exit(EXIT_FAILURE), and thus avoid the need to > >>> special case flushing the monitor. > >> > >> And presumably add an atexit handler to flush the monitor ala monitor_abort. > >> AFAICT currently no destructor is called for the monitor at exit time. > > > > The HMP monitor flushes at each newline, and exit() will take care of > > flushing stdout, so I don't think there's anything else needed. > > > >>> Also I think there's a decent case to be made for error_report() > >>> to call monitor_flush(). > >> > >> A good start, but that would not help for monitors with skip_flush=true, which > >> need to format the buffered string in a json response, which is the case I > >> tripped over. > > > > 'skip_flush' is only set to 'true' when using a QMP monitor and invoking > > "hmp-monitor-command". > > OK, that is narrower than I thought. Now I see that other QMP monitors send > error_report() to stderr, hence it is visible after abort and exit: > > int error_vprintf(const char *fmt, va_list ap) { > if (cur_mon && !monitor_cur_is_qmp()) > return monitor_vprintf(cur_mon, fmt, ap); > return vfprintf(stderr, fmt, ap); <-- HERE > > That surprises me, I thought that would be returned to the monitor caller in the > json response. I guess the rationale is that the "main" error, if any, will be > set and returned by the err object that is passed down the stack during command > evaluation. > > > In such a case, the error message needs to be built into a JSON error > > reply and sent over the socket. Your patch doesn't help this case > > since you've just printed to stderr. > > Same as vfprintf above! > > > I don't think it is reasonable > > to expect QMP monitors to send replies on SIG_ABRT anyway. > > I agree. My patch causes the error to be seen somewhere, anywhere, instead > of being dropped on the floor. > > > So I don't > > think the skip_flush=true scenario is a problem to be concerned with. > > It is indeed a narrow case, and not worth much effort or code change. > I'm inclined to drop it, but I appreciate the time you have spent reviewing it. If you know of scenarios that can trigger abort() as a result of either QMP or HMP commands, then we still need to fix those. Nothing that is reachable from the monitor commands should ever end up in abort(), as a general rule. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|