Xorg hangs use 99% of CPU on systemd reboot

[Barry Scott]

On Fri 03 Jul 2015 16:14:13 Peter Hutterer wrote:
> On Thu, Jul 02, 2015 at 04:26:19PM +0100, Barry Scott wrote:
> > The attached patch works around an issue we hit after we
> > ported from Fedora 20 to Fedora 21.
> > 
> > When systemd reboot starts something happens to dbus that
> > causes Xorg to loop hard using 99% CPU in WaitForSomething.
> > 
> > The reason for the loop is that the bus_info.fd in dbus-core.c
> > has been closed. But the expected Disconnected signal is not
> > received by the messages filter.
> 
> wouldn't it be better to set up the filter so we get the disconnect signal?

The dbus ping example does not add a filter to see Disconnected.
https://github.com/sgh/dbus-examples/blob/master/dbus-ping-listen.c

Barry

> 
> Cheers,
>    Peter
> 
> > The patch works around this issue by removing the fd from the
> > fd_set that is feed into the Select in WaitForSomething by
> > calling RemoveGeneralSocket from within wakeup_handler in
> > dbus-core.c.
> > 
> > When systemctl is used to stop and restart Xorg outside of the
> > reboot it works without any problems.
> > 
> > Barry
> > 
> > 
> > From ca770dd6e8ebb9a780ce68a07535f976f6120247 Mon Sep 17 00:00:00 2001
> > From: Barry Scott <barry.scott at onelan.co.uk>
> > Date: Tue, 30 Jun 2015 15:58:22 +0100
> > Subject: [PATCH] server loops in WaitForSomething when dbus closed by
> > systemd> 
> >  shutdown
> > 
> > Work around issue with dbus fd becoming closed by WaitForSomething
> > still using it in Select. The Select return EBADF but becuase the dbus fd
> > is not taken out of the fs_set the code loop forever.
> > 
> > This state has been seen when systemd starts to shutdown on Fedora 21.
> > 
> > Signed-off-by: Barry Scott <barry.scott at onelan.co.uk>
> > ---
> > 
> >  config/dbus-core.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/config/dbus-core.c b/config/dbus-core.c
> > index 8351ea4..fac8116 100644
> > --- a/config/dbus-core.c
> > +++ b/config/dbus-core.c
> > @@ -52,6 +52,19 @@ wakeup_handler(void *data, int num_fds, void
> > *read_mask)
> > 
> >  {
> >  
> >      struct dbus_core_info *info = data;
> > 
> > +    if (info->fd < 0) {
> > +        return;
> > +    }
> > +
> > +    if (!dbus_connection_get_is_connected(info->connection)) {
> > +        /* must remove the FD here as WaitForSomething's Select will now
> > fail +           and WaitForSomething will loop hard calling Select.
> > +           The "Disconnected" message has been seen to not arrive. */
> > +        RemoveGeneralSocket(info->fd);
> > +        info->fd = -1;
> > +        return;
> > +    }
> > +
> > 
> >      if (info->connection && num_fds > 0 && FD_ISSET(info->fd, (fd_set *)
> >      read_mask)) {>      
> >          do {
> >          
> >              dbus_connection_read_write_dispatch(info->connection, 0);
> > 
> > _______________________________________________
> > xorg-devel at lists.x.org: X.Org development
> > Archives: http://lists.x.org/archives/xorg-devel
> > Info: http://lists.x.org/mailman/listinfo/xorg-devel

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