From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54757) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gTibk-00024Z-0P for qemu-devel@nongnu.org; Mon, 03 Dec 2018 02:25:35 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gTiNQ-0006mK-Mm for qemu-devel@nongnu.org; Mon, 03 Dec 2018 02:10:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46008) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gTiNQ-0006lr-EZ for qemu-devel@nongnu.org; Mon, 03 Dec 2018 02:10:44 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8C202307D915 for ; Mon, 3 Dec 2018 07:10:43 +0000 (UTC) From: Markus Armbruster References: <20181029125733.14597-1-marcandre.lureau@redhat.com> <20181029125733.14597-3-marcandre.lureau@redhat.com> Date: Mon, 03 Dec 2018 08:10:37 +0100 In-Reply-To: <20181029125733.14597-3-marcandre.lureau@redhat.com> (=?utf-8?Q?=22Marc-Andr=C3=A9?= Lureau"'s message of "Mon, 29 Oct 2018 16:57:29 +0400") Message-ID: <87in0b84r6.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v2 2/6] monitor: accept chardev input from iothread List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Cc: qemu-devel@nongnu.org, Paolo Bonzini , "Dr. David Alan Gilbert" , peterx@redhat.com Marc-Andr=C3=A9 Lureau writes: > Chardev backends may not handle safely IO events from concurrent > threads. What exactly could go wrong? Or is this a well-known fact that doesn't need further elaboration? "safely handle I/O events" > Better to wake up the chardev from the monitor IO thread if > it's being used as the chardev context. > > Unify code paths by using a BH in all cases. > > Drop the now redundant aio_notify() call. > > Signed-off-by: Marc-Andr=C3=A9 Lureau > --- > monitor.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/monitor.c b/monitor.c > index 07712d89f9..511dd11d1c 100644 > --- a/monitor.c > +++ b/monitor.c > @@ -4304,6 +4304,13 @@ int monitor_suspend(Monitor *mon) > return 0; > } >=20=20 > +static void monitor_accept_input(void *opaque) > +{ > + Monitor *mon =3D opaque; > + > + qemu_chr_fe_accept_input(&mon->chr); > +} > + > void monitor_resume(Monitor *mon) > { > if (monitor_is_hmp_non_interactive(mon)) { > @@ -4311,20 +4318,24 @@ void monitor_resume(Monitor *mon) > } >=20=20 > if (atomic_dec_fetch(&mon->suspend_cnt) =3D=3D 0) { > + AioContext *ctx =3D qemu_get_aio_context(); > + > if (monitor_is_qmp(mon)) { > /* > * For QMP monitors that are running in the I/O thread, > * let's kick the thread in case it's sleeping. > */ > if (mon->use_io_thread) { > - aio_notify(iothread_get_aio_context(mon_iothread)); > + ctx =3D iothread_get_aio_context(mon_iothread); > } > } else { > assert(mon->rs); > readline_show_prompt(mon->rs); > } Correct, since mon->use_io_thread can only be true in a QMP monitor so far. But there's no need to depend on that here: AioContext *ctx; if (mon->use_io_thread) { ctx =3D iothread_get_aio_context(mon_iothread); } else { ctx =3D qemu_get_aio_context(); } if (!monitor_is_qmp(mon)) { assert(mon->rs); readline_show_prompt(mon->rs); } Same in monitor_suspend(), by the way. The dependence in monitor_init() is tolerable, because it's the place where the dependence is established. > - qemu_chr_fe_accept_input(&mon->chr); > + > + aio_bh_schedule_oneshot(ctx, monitor_accept_input, mon); > } > + > trace_monitor_suspend(mon, -1); > }