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?

Peter,

My, limited, understanding of dbus is that the signal does not need to be enabled, it 
should just turn up. But it does not in the case where systemd
has started to shutdown the system.

Asking the service that we use to control Xorg to stop always works
and the Disconnect signal is received. It only in the case of systemd
doing the shutdown that the signal is not received.

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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