From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60769) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f12IA-0008G3-Me for qemu-devel@nongnu.org; Wed, 28 Mar 2018 00:02:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f12I5-0004vT-QI for qemu-devel@nongnu.org; Wed, 28 Mar 2018 00:02:30 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:47380 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f12I5-0004vB-K2 for qemu-devel@nongnu.org; Wed, 28 Mar 2018 00:02:25 -0400 Date: Wed, 28 Mar 2018 12:02:09 +0800 From: Peter Xu Message-ID: <20180328040209.GA29554@xz-mi> References: <20180309090006.10018-1-peterx@redhat.com> <20180309090006.10018-15-peterx@redhat.com> <20180326080738.GA17789@xz-mi> <20180326090822.GC17789@xz-mi> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v8 14/23] monitor: separate QMP parser and dispatcher List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Cc: QEMU , Laurent Vivier , Fam Zheng , Juan Quintela , Michael Roth , Markus Armbruster , Stefan Hajnoczi , Paolo Bonzini , "Dr . David Alan Gilbert" On Mon, Mar 26, 2018 at 11:46:13AM +0200, Marc-Andr=C3=A9 Lureau wrote: > Hi >=20 > On Mon, Mar 26, 2018 at 11:08 AM, Peter Xu wrote: > > On Mon, Mar 26, 2018 at 10:33:27AM +0200, Marc-Andr=C3=A9 Lureau wrot= e: > >> Hi > >> > >> On Mon, Mar 26, 2018 at 10:07 AM, Peter Xu wrote= : > >> > On Fri, Mar 23, 2018 at 05:18:53PM +0100, Marc-Andr=C3=A9 Lureau w= rote: > >> > > >> > [...] > >> > > >> >> > +/* > >> >> > + * Dispatch one single QMP request. The function will free the= req_obj > >> >> > + * and objects inside it before return. > >> >> > + */ > >> >> > +static void monitor_qmp_dispatch_one(QMPRequest *req_obj) > >> >> > { > >> >> > - QObject *req, *rsp =3D NULL, *id =3D NULL; > >> >> > + Monitor *mon, *old_mon; > >> >> > + QObject *req, *rsp =3D NULL, *id; > >> >> > QDict *qdict =3D NULL; > >> >> > - MonitorQMP *mon_qmp =3D container_of(parser, MonitorQMP, p= arser); > >> >> > - Monitor *old_mon, *mon =3D container_of(mon_qmp, Monitor, = qmp); > >> >> > - > >> >> > - Error *err =3D NULL; > >> >> > + bool need_resume; > >> >> > > >> >> > - req =3D json_parser_parse_err(tokens, NULL, &err); > >> >> > - if (!req && !err) { > >> >> > - /* json_parser_parse_err() sucks: can fail without set= ting @err */ > >> >> > - error_setg(&err, QERR_JSON_PARSING); > >> >> > - } > >> >> > - if (err) { > >> >> > - goto err_out; > >> >> > - } > >> >> > + req =3D req_obj->req; > >> >> > + mon =3D req_obj->mon; > >> >> > + id =3D req_obj->id; > >> >> > + need_resume =3D req_obj->need_resume; > >> >> > > >> >> > - qdict =3D qobject_to_qdict(req); > >> >> > - if (qdict) { > >> >> > - id =3D qdict_get(qdict, "id"); > >> >> > - qobject_incref(id); > >> >> > - qdict_del(qdict, "id"); > >> >> > - } /* else will fail qmp_dispatch() */ > >> >> > + g_free(req_obj); > >> >> > > >> >> > if (trace_event_get_state_backends(TRACE_HANDLE_QMP_COMMAN= D)) { > >> >> > QString *req_json =3D qobject_to_json(req); > >> >> > @@ -3900,7 +3932,7 @@ static void handle_qmp_command(JSONMessag= eParser *parser, GQueue *tokens) > >> >> > old_mon =3D cur_mon; > >> >> > cur_mon =3D mon; > >> >> > >> >> There is another issue with this series, since cur_mon is global = (and > >> >> not protected), an oob command may change the cur_mon while anoth= er > >> >> command is running in the main thread with unexpected consequence= s. I > >> >> don't have a clear idea what is the best way to solve it. Making = the > >> >> variable per-thread, or going all the way to get rid of cur_mon (= my > >> >> preference, but much harder) > >> > > >> > IMHO it is fine too. > >> > > >> > Note that this cur_mon operation is in monitor_qmp_dispatch_one() = now, > >> > which is still running in main thread. So AFAICT all the cur_mon > >> > references are in main thread, and monitor IOThread does not modif= y > >> > that variable at all. Then we should probably be safe. > >> > >> But monitor_qmp_dispatch_one() is called from iothread if the comman= d > >> is oob, so cur_mon may be updated while another command is running i= n > >> main thread, or am I wrong? > > > > You are right. I missed that, sorry... > > > > Would this be a simple workaround (but hopefully efficient) solution? > > > > diff --git a/monitor.c b/monitor.c > > index 77f4c41cfa..99641c0c6d 100644 > > --- a/monitor.c > > +++ b/monitor.c > > @@ -4023,7 +4023,7 @@ typedef struct QMPRequest QMPRequest; > > * Dispatch one single QMP request. The function will free the req_o= bj > > * and objects inside it before return. > > */ > > -static void monitor_qmp_dispatch_one(QMPRequest *req_obj) > > +static void monitor_qmp_dispatch_one(QMPRequest *req_obj, bool hack_= curmon) > > { > > Monitor *mon, *old_mon; > > QObject *req, *rsp =3D NULL, *id; > > @@ -4043,12 +4043,16 @@ static void monitor_qmp_dispatch_one(QMPReque= st *req_obj) > > QDECREF(req_json); > > } > > > > - old_mon =3D cur_mon; > > - cur_mon =3D mon; > > + if (hack_curmon) { > > + old_mon =3D cur_mon; > > + cur_mon =3D mon; > > + } > > > > rsp =3D qmp_dispatch(mon->qmp.commands, req); > > > > - cur_mon =3D old_mon; > > + if (hack_curmon) { > > + cur_mon =3D old_mon; > > + } > > > > if (mon->qmp.commands =3D=3D &qmp_cap_negotiation_commands) { > > qdict =3D qdict_get_qdict(qobject_to(QDict, rsp), "error"); > > @@ -4116,7 +4120,7 @@ static void monitor_qmp_bh_dispatcher(void *dat= a) > > > > if (req_obj) { > > trace_monitor_qmp_cmd_in_band(qobject_get_try_str(req_obj->i= d) ?: ""); > > - monitor_qmp_dispatch_one(req_obj); > > + monitor_qmp_dispatch_one(req_obj, true); > > /* Reschedule instead of looping so the main loop stays resp= onsive */ > > qemu_bh_schedule(mon_global.qmp_dispatcher_bh); > > } > > @@ -4175,7 +4179,7 @@ static void handle_qmp_command(JSONMessageParse= r *parser, GQueue *tokens) > > /* Out-Of-Band (OOB) requests are executed directly in parse= r. */ > > trace_monitor_qmp_cmd_out_of_band(qobject_get_try_str(req_ob= j->id) > > ?: ""); > > - monitor_qmp_dispatch_one(req_obj); > > + monitor_qmp_dispatch_one(req_obj, false); > > return; > > } > > > > Then we forbit touching that evil cur_mon in OOB-capable command > > handlers. Thanks, >=20 > That's not easy to enforce though, afaict it is being used for: > - error reporting decision IMO this should not be a problem, since any QMP handler (including OOB-capable ones) will be with an Error** there, so logically speaking people should never call things like error_report() in that. > - file & socket lookup (fd: & /dev/fdset etc) I suppose only very rare commands will use it? It'll be a big problem to solve when we want to completely remove cur_mon though. > - the current state of the monitor / list of commands, cpu_path, capabi= lities.. This is very rare to be used too? Most commands should not use them AFAI= U. >=20 > Wouldn't it be simpler to make it per-thread? I think it could also > use helpers to push/pop the current monitor. Anyway I think yes this is still a good option (though the cur_mon logic will be a bit more complicated). Do you plan to post some patch about this, or do you want me to do this? I suppose we'll change the qemu_thread_create() a bit to pass the cur_mon inside, and I suppose this might be better material after 2.12 release if OOB is off now. --=20 Peter Xu