From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54859) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f50bV-0001tV-5E for qemu-devel@nongnu.org; Sat, 07 Apr 2018 23:02:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f50bR-0002Rr-W0 for qemu-devel@nongnu.org; Sat, 07 Apr 2018 23:02:53 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:41854 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 1f50bR-0002RE-QT for qemu-devel@nongnu.org; Sat, 07 Apr 2018 23:02:49 -0400 Date: Sun, 8 Apr 2018 11:02:36 +0800 From: Peter Xu Message-ID: <20180408030236.GC10540@xz-mi> References: <20180309090006.10018-1-peterx@redhat.com> <20180309090006.10018-15-peterx@redhat.com> <20180326080738.GA17789@xz-mi> <20180326090822.GC17789@xz-mi> <20180328040209.GA29554@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 Wed, Apr 04, 2018 at 03:58:56PM +0200, Marc-Andr=C3=A9 Lureau wrote: > Hi Peter >=20 > On Wed, Mar 28, 2018 at 6:02 AM, Peter Xu wrote: > > On Mon, Mar 26, 2018 at 11:46:13AM +0200, Marc-Andr=C3=A9 Lureau wrot= e: > >> Hi > >> > >> 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 w= rote: > >> >> Hi > >> >> > >> >> On Mon, Mar 26, 2018 at 10:07 AM, Peter Xu wr= ote: > >> >> > On Fri, Mar 23, 2018 at 05:18:53PM +0100, Marc-Andr=C3=A9 Lurea= u wrote: > >> >> > > >> >> > [...] > >> >> > > >> >> >> > +/* > >> >> >> > + * 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= , parser); > >> >> >> > - Monitor *old_mon, *mon =3D container_of(mon_qmp, Monito= r, 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 = setting @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_COM= MAND)) { > >> >> >> > QString *req_json =3D qobject_to_json(req); > >> >> >> > @@ -3900,7 +3932,7 @@ static void handle_qmp_command(JSONMes= sageParser *parser, GQueue *tokens) > >> >> >> > old_mon =3D cur_mon; > >> >> >> > cur_mon =3D mon; > >> >> >> > >> >> >> There is another issue with this series, since cur_mon is glob= al (and > >> >> >> not protected), an oob command may change the cur_mon while an= other > >> >> >> command is running in the main thread with unexpected conseque= nces. I > >> >> >> don't have a clear idea what is the best way to solve it. Maki= ng the > >> >> >> variable per-thread, or going all the way to get rid of cur_mo= n (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_m= on > >> >> > references are in main thread, and monitor IOThread does not mo= dify > >> >> > that variable at all. Then we should probably be safe. > >> >> > >> >> But monitor_qmp_dispatch_one() is called from iothread if the com= mand > >> >> is oob, so cur_mon may be updated while another command is runnin= g in > >> >> main thread, or am I wrong? > >> > > >> > You are right. I missed that, sorry... > >> > > >> > Would this be a simple workaround (but hopefully efficient) soluti= on? > >> > > >> > 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 re= q_obj > >> > * 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 ha= ck_curmon) > >> > { > >> > Monitor *mon, *old_mon; > >> > QObject *req, *rsp =3D NULL, *id; > >> > @@ -4043,12 +4043,16 @@ static void monitor_qmp_dispatch_one(QMPRe= quest *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 *= data) > >> > > >> > if (req_obj) { > >> > trace_monitor_qmp_cmd_in_band(qobject_get_try_str(req_obj= ->id) ?: ""); > >> > - monitor_qmp_dispatch_one(req_obj); > >> > + monitor_qmp_dispatch_one(req_obj, true); > >> > /* Reschedule instead of looping so the main loop stays r= esponsive */ > >> > qemu_bh_schedule(mon_global.qmp_dispatcher_bh); > >> > } > >> > @@ -4175,7 +4179,7 @@ static void handle_qmp_command(JSONMessagePa= rser *parser, GQueue *tokens) > >> > /* Out-Of-Band (OOB) requests are executed directly in pa= rser. */ > >> > trace_monitor_qmp_cmd_out_of_band(qobject_get_try_str(req= _obj->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, > >> > >> 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 speakin= g > > 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 proble= m > > to solve when we want to completely remove cur_mon though. > > > >> - the current state of the monitor / list of commands, cpu_path, cap= abilities.. > > > > This is very rare to be used too? Most commands should not use them = AFAIU. > > > >> > >> 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 > Have you looked at making cur_mon per-thread? Above was my idea, nothing else has been done. Please feel free to post a patch for this, or I'll do this after 2.12 release. --=20 Peter Xu