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 lists1p.gnu.org (lists1p.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 B0D2AF9936C for ; Thu, 23 Apr 2026 10:58:45 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wFrl1-0000uY-Gr; Thu, 23 Apr 2026 06:58:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wFrkv-0000tB-A6 for qemu-devel@nongnu.org; Thu, 23 Apr 2026 06:58:03 -0400 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 1wFrkt-000559-QB for qemu-devel@nongnu.org; Thu, 23 Apr 2026 06:58:01 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1776941878; 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=RY5j7jHOGxkGDi70dG5O6OtLWIXA4C1iW6USZ+Rp52c=; b=hxkihzkE6bIm+1Rxi8b9tjHQbNJoR51fliT4XdZtW4sNPZnVL46FiXc5fc9v/bMgUUO2hE waT5PczQzca2UgGKu7/Bg9tx8ItD3ReLuBXmOhfgvxWUUZ9bhOrOLl923GyLGn2RA2Rwqf LZ/6344nEs5WgdJvcBllzfEZHfEFUDs= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-629-7PWjdNy8MHaOYdZwxZKLuw-1; Thu, 23 Apr 2026 06:57:57 -0400 X-MC-Unique: 7PWjdNy8MHaOYdZwxZKLuw-1 X-Mimecast-MFC-AGG-ID: 7PWjdNy8MHaOYdZwxZKLuw_1776941876 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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 mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7E041195605A for ; Thu, 23 Apr 2026 10:57:56 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.30]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3D0171800351 for ; Thu, 23 Apr 2026 10:57:56 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id B53FD21E6A28; Thu, 23 Apr 2026 12:57:53 +0200 (CEST) From: Markus Armbruster To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Cc: qemu-devel@nongnu.org Subject: Re: [PATCH] ui/console: remove console from global list on finalization In-Reply-To: (=?utf-8?Q?=22Marc-Andr=C3=A9?= Lureau"'s message of "Thu, 23 Apr 2026 12:02:16 +0400") References: <20260422202646.272081-1-marcandre.lureau@redhat.com> <87v7dis20c.fsf@pond.sub.org> <87y0ieqhzz.fsf@pond.sub.org> Date: Thu, 23 Apr 2026 12:57:53 +0200 Message-ID: <87zf2undu6.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Marc-Andr=C3=A9 Lureau writes: > Hi > > On Thu, Apr 23, 2026 at 10:59=E2=80=AFAM Markus Armbruster wrote: >> >> Marc-Andr=C3=A9 Lureau writes: >> >> > Hi >> > >> > On Thu, Apr 23, 2026 at 9:02=E2=80=AFAM Markus Armbruster wrote: >> >> >> >> marcandre.lureau@redhat.com writes: >> >> >> >> > From: Marc-Andr=C3=A9 Lureau >> >> > >> >> > This commit removes the QemuConsole from the global "consoles" list= when >> >> > it is finalized. >> >> > >> >> > Previously, there was a TODO comment indicating this path needed >> >> > checking. The assertions added ensure that `dcls`, `gl_block`, and = the >> >> > `dump_queue` are empty before removal, confirming the console is in= a >> >> > clean state. >> >> > >> >> > Fix potential use-after-free crashes when a display console is remo= ved. >> >> > >> >> > Reported-by: Markus Armbruster >> >> > Signed-off-by: Marc-Andr=C3=A9 Lureau >> >> > --- >> >> > ui/console.c | 5 ++++- >> >> > 1 file changed, 4 insertions(+), 1 deletion(-) >> >> > >> >> > diff --git a/ui/console.c b/ui/console.c >> >> > index f445db11389..b64e2122f34 100644 >> >> > --- a/ui/console.c >> >> > +++ b/ui/console.c >> >> > @@ -394,10 +394,13 @@ qemu_console_finalize(Object *obj) >> >> > { >> >> > QemuConsole *c =3D QEMU_CONSOLE(obj); >> >> > >> >> > - /* TODO: check this code path, and unregister from consoles */ >> >> > + assert(c->dcls =3D=3D 0); >> >> > + assert(c->gl_block =3D=3D 0); >> >> > + assert(qemu_co_queue_empty(&c->dump_queue)); >> >> >> >> Help me out: what ensures this? >> > >> > - No display change listener left >> > - No GL lock left >> > - No pending screendump >> >> Yes, but what ensures none of these are left / pending by the time we >> finalize? > > Unfortunately, we don't have much support for unplugging display > consoles. So those asserts are mostly there to remind us of further > issues.. I should probably leave the TODO. > > In general graphics devices do not support hot-plugging. It looks like > we are missing a couple of hotpluggable =3D false in hw/display. I trust you'll take care of them. > So, it > should not be reachable today but by using low-level QMP/QOM like in > this test. Due to QOM's design, introspection must create and destroy a temporary object. This must not have observable side effects. Devices have a life cycle supporting this: instance_init -+-> realize ---> unrealize -+-> instance_finalize. | | +---------------------------+ We can keep instance_init and instance_finalize free of side effects by doing them in realize and unrealize instead. Non-device objects lack realize / unrealize. I believe the wheel has been reinvented a few times there. Back to qemu_console_finalize(). I guess the correctness argument goes roughly like this: 1. After initialization, these assertions hold. 2. Therefore, immediate finalize works. QOM introspection works. 3. Non-immediate finalization cannot happen. Is this about right? > Text console/VC is also poorly supported and leaks, so it will never > reach qemu_console_finalize() either. > > I can try to improve the situation by sending a more complete series, > so those assert() are unlikely to be reachable in the future. I'm just trying to understand why this works :) More complete patches are always nice, but I'm not demanding you do that now. Comments perhaps? >> >> > g_clear_pointer(&c->surface, qemu_free_displaysurface); >> >> > g_clear_pointer(&c->gl_unblock_timer, timer_free); >> >> > g_clear_pointer(&c->ui_timer, timer_free); >> >> > + QTAILQ_REMOVE(&consoles, c, next); >> >> >> >> Is @consoles only accessed from the main thread? >> > >> > Yes, the UI code is main thread only. >> >> Good, thanks! >>