On Wed, Aug 24, 2022 at 05:40:27PM +0800, Bin Meng wrote: > From: Bin Meng <bin.m...@windriver.com> > > Random failure was observed when running qtests on Windows due to > "Broken pipe" detected by qmp_fd_receive(). What happened is that > the qtest executable sends testing data over a socket to the QEMU > under test but no response is received. The errno of the recv() > call from the qtest executable indicates ETIMEOUT, due to the qmp > chardev's tcp_chr_read() is never called to receive testing data > hence no response is sent to the other side. > > tcp_chr_read() is registered as the callback of the socket watch > GSource. The reason of the callback not being called by glib, is > that the source check fails to indicate the source is ready. There > are two socket watch sources created to monitor the same socket > event object from the char-socket backend in update_ioc_handlers(). > During the source check phase, qio_channel_socket_source_check() > calls WSAEnumNetworkEvents() to discovers occurrences of network > events for the indicated socket, clear internal network event records, > and reset the event object. Testing shows that if we don't reset the > event object by not passing the event handle to WSAEnumNetworkEvents() > the symptom goes away and qtest runs very stably. > > It looks we don't need to call WSAEnumNetworkEvents() at all, as we > don't parse the result of WSANETWORKEVENTS returned from this API. > We use select() to poll the socket status. Fix this instability by > dropping the WSAEnumNetworkEvents() call. > > Signed-off-by: Bin Meng <bin.m...@windriver.com> > --- > During the testing, I removed the following codes in update_ioc_handlers(): > > remove_hup_source(s); > s->hup_source = qio_channel_create_watch(s->ioc, G_IO_HUP); > g_source_set_callback(s->hup_source, (GSourceFunc)tcp_chr_hup, > chr, NULL); > g_source_attach(s->hup_source, chr->gcontext); > > and such change also makes the symptom go away. > > And if I moved the above codes to the beginning, before the call to > io_add_watch_poll(), the symptom also goes away. > > It seems two sources watching on the same socket event object is > the key that leads to the instability. The order of adding a source > watch seems to also play a role but I can't explain why. > Hopefully a Windows and glib expert could explain this behavior. > > io/channel-watch.c | 4 ---- > 1 file changed, 4 deletions(-)
Reviewed-by: Daniel P. Berrangé <berra...@redhat.com> and queued With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
