From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49088) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gX1Uh-0000vw-Ul for qemu-devel@nongnu.org; Wed, 12 Dec 2018 05:11:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gX1Uh-0003RB-2n for qemu-devel@nongnu.org; Wed, 12 Dec 2018 05:11:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33290) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gX1Ug-0003QM-Qk for qemu-devel@nongnu.org; Wed, 12 Dec 2018 05:11:55 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1476B3001FE5 for ; Wed, 12 Dec 2018 10:11:54 +0000 (UTC) From: Markus Armbruster Date: Wed, 12 Dec 2018 11:11:41 +0100 Message-Id: <20181212101145.3496-8-armbru@redhat.com> In-Reply-To: <20181212101145.3496-1-armbru@redhat.com> References: <20181212101145.3496-1-armbru@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: [Qemu-devel] [PULL 07/11] monitor: avoid potential dead-lock when cleaning up List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= From: Marc-Andr=C3=A9 Lureau When a monitor is connected to a Spice chardev, the monitor cleanup can dead-lock: #0 0x00007f43446637fd in __lll_lock_wait () at /lib64/libpthread.so.0 #1 0x00007f434465ccf4 in pthread_mutex_lock () at /lib64/libpthread.so.= 0 #2 0x0000556dd79f22ba in qemu_mutex_lock_impl (mutex=3D0x556dd81c9220 <= monitor_lock>, file=3D0x556dd7ae3648 "/home/elmarco/src/qq/monitor.c", li= ne=3D645) at /home/elmarco/src/qq/util/qemu-thread-posix.c:66 #3 0x0000556dd7431bd5 in monitor_qapi_event_queue (event=3DQAPI_EVENT_S= PICE_DISCONNECTED, qdict=3D0x556dd9abc850, errp=3D0x7fffb7bbddd8) at /hom= e/elmarco/src/qq/monitor.c:645 #4 0x0000556dd79d476b in qapi_event_send_spice_disconnected (server=3D0= x556dd98ee760, client=3D0x556ddaaa8560, errp=3D0x556dd82180d0 ) at qapi/qapi-events-ui.c:149 #5 0x0000556dd7870fc1 in channel_event (event=3D3, info=3D0x556ddad1b59= 0) at /home/elmarco/src/qq/ui/spice-core.c:235 #6 0x00007f434560a6bb in reds_handle_channel_event (reds=3D, event=3D3, info=3D0x556ddad1b590) at reds.c:316 #7 0x00007f43455f393b in main_dispatcher_self_handle_channel_event (inf= o=3D0x556ddad1b590, event=3D3, self=3D0x556dd9a7d8c0) at main-dispatcher.= c:197 #8 0x00007f43455f393b in main_dispatcher_channel_event (self=3D0x556dd9= a7d8c0, event=3Devent@entry=3D3, info=3D0x556ddad1b590) at main-dispatche= r.c:197 #9 0x00007f4345612833 in red_stream_push_channel_event (s=3Ds@entry=3D0= x556ddae2ef40, event=3Devent@entry=3D3) at red-stream.c:414 #10 0x00007f434561286b in red_stream_free (s=3D0x556ddae2ef40) at red-st= ream.c:388 #11 0x00007f43455f9ddc in red_channel_client_finalize (object=3D0x556dd9= bb21a0) at red-channel-client.c:347 #12 0x00007f434b5f9fb9 in g_object_unref () at /lib64/libgobject-2.0.so.= 0 #13 0x00007f43455fc212 in red_channel_client_push (rcc=3D0x556dd9bb21a0)= at red-channel-client.c:1341 #14 0x0000556dd76081ba in spice_port_set_fe_open (chr=3D0x556dd9925e20, = fe_open=3D0) at /home/elmarco/src/qq/chardev/spice.c:241 #15 0x0000556dd796d74a in qemu_chr_fe_set_open (be=3D0x556dd9a37c00, fe_= open=3D0) at /home/elmarco/src/qq/chardev/char-fe.c:340 #16 0x0000556dd796d4d9 in qemu_chr_fe_set_handlers (b=3D0x556dd9a37c00, = fd_can_read=3D0x0, fd_read=3D0x0, fd_event=3D0x0, be_change=3D0x0, opaque= =3D0x0, context=3D0x0, set_open=3Dtrue) at /home/elmarco/src/qq/chardev/c= har-fe.c:280 #17 0x0000556dd796d359 in qemu_chr_fe_deinit (b=3D0x556dd9a37c00, del=3D= false) at /home/elmarco/src/qq/chardev/char-fe.c:233 #18 0x0000556dd7432240 in monitor_data_destroy (mon=3D0x556dd9a37c00) at= /home/elmarco/src/qq/monitor.c:786 #19 0x0000556dd743b968 in monitor_cleanup () at /home/elmarco/src/qq/mon= itor.c:4683 #20 0x0000556dd75ce776 in main (argc=3D3, argv=3D0x7fffb7bbe458, envp=3D= 0x7fffb7bbe478) at /home/elmarco/src/qq/vl.c:4660 Because spice code tries to emit a "disconnected" signal on the monitors. Fix this dead-lock by releasing the monitor lock for flush/destroy. monitor_lock protects mon_list, monitor_qapi_event_state and monitor_destroyed. monitor_flush() and monitor_data_destroy() don't access any of those variables. monitor_cleanup()'s loop is safe because it uses QTAILQ_FOREACH_SAFE(), and no further monitor can be added after calling monitor_cleanup() thanks to monitor_destroyed check in monitor_list_append(). Signed-off-by: Marc-Andr=C3=A9 Lureau Reviewed-by: Markus Armbruster Message-Id: <20181205203737.9011-8-marcandre.lureau@redhat.com> Signed-off-by: Markus Armbruster --- monitor.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/monitor.c b/monitor.c index d353c0e645..5ce2c58b76 100644 --- a/monitor.c +++ b/monitor.c @@ -4651,8 +4651,11 @@ void monitor_cleanup(void) monitor_destroyed =3D true; QTAILQ_FOREACH_SAFE(mon, &mon_list, entry, next) { QTAILQ_REMOVE(&mon_list, mon, entry); + /* Permit QAPI event emission from character frontend release */ + qemu_mutex_unlock(&monitor_lock); monitor_flush(mon); monitor_data_destroy(mon); + qemu_mutex_lock(&monitor_lock); g_free(mon); } qemu_mutex_unlock(&monitor_lock); --=20 2.17.2