Bug 1250105

Description of problem:
on el6.7, some older X11 apps which have happened to work just fine on el6.0, el6.1, el6.2, etc.. up to and including el6.6 (with the latest el6.7 updates) display garbage in the X11 icons where backingstore was requested.

Relevant client-side code is related to this:
     XGetWindowAttributes(xv_display(info), xv_xid(info), &wattrs);
  127     switch (wattrs.backing_store) {
  128       case Always:
  129       case WhenMapped:
  130     return wattrs.backing_store;
  131 
  132       default:
  133     return FALSE;
  134     }

Notice the wattrs.backing_store.

Version-Release number of selected component (if applicable):

I have verified this on el6.7 using the NVidia, vmware and ast drivers so it seems it's in the core Xorg components.
The 'garbage' actualls looks like some other parts of the X11 root window in some cases.. Perhaps that's just a wrong pointer somewhere. I'll send screenshots later.

How reproducible:

100%

Steps to Reproduce:
1. update to el6.7
2. fire up an apps that makes use of the wattrs.backing_store attributes (XGetWindowAttributes).
3. observe garbage in place of the above X11 icons.

Actual results:


Expected results:
The icons/windows should come up fine.

Additional info:

Please note that it still does work fine when the apps are run against an Xvnc server.. most likely because Xvnc doesn't support backingstore at all.

Additional info:

Where are you experiencing the behavior?  What environment?

Issue happens on any el6.7 x86_64 machine with an xorg Xserver with backingstore enabled.
Issue does -NOT- happen on any el6.0 to el6.6 system.

When does the behavior occur? Frequently?  Repeatedly?   At certain times?

This behaviour is consistent across most X servers on el6.7. Xvnc doesn't seem to be affected but I suspect this is because Xvnc (the X server) may not have an implementation of 'BackingStore/SaveUnders'.

What information can you provide around timeframes and urgency?

This is not an urgent issue. It's just a regression that I noticed and wanted to report.

Hello,
On a side note, when starting the X server with '-bs', the problem doesn't show up so it seems directly related to BackingStore.
I wonder what broke between el6.6 and el6.7.
Vincent

*** Bug 1255750 has been marked as a duplicate of this bug. ***

Created attachment 1066947 [details]
Screenshot showing normal behaviour (6.0 to 6.6 and 6.6 without bs)

Created attachment 1066948 [details]
Screenshot showing backingstore enabled icons with wrong content.

Notice how some of the graphics garbage looks like other parts of the root window.

Maybe same problem. We have an old X11 application that broke with similar symptoms. The main cause is the el6.7 xorg server is not sending "expose" events. MacOS (and el6.6 servers) do send the "expose" events.

I see a comment about "Fix backing store's Always mode" in "Wed Feb 25 2015 Adam Jackson <ajax> 1.15.0-32", maybe it is related? Is there more information about this change? a bug report? a bugzilla reference?
K.O.

Konstantin,
Hmmm, this could be related. Trying disabling 'Backing Store' by adding '-bs' to the X server command line..
Mine now looks like this:
/usr/bin/X -bs -auth /var/run/slim/slim.auth

(Note that I am running SLiM, not GDM).
Vincent

The el7.1 xorg server is generating the "expose" events as expected. version is xorg-x11-server-Xorg-1.15.0-33.el7_1.x86_64. So we have a mismatch between 6.6, 7.1 (expose ok) and 6.7 (expose missing). K.O.

(In reply to Vincent S. Cojot from comment #10)
> Hmmm, this could be related. Trying disabling 'Backing Store' by adding
> '-bs' to the X server command line..

In our case, the application itself requests "backing store". It does not work without backing store (either self requested or via global "-bs").

The present problem was resolved by making it process "visibility notify" events instead of "expose" events.

K.O.

Dear Vincent,

do you have 6.8 Alpha with newest packages available? If so it is working for you?

Thanks
-Tom

Dear Tomas,
Thanks for working on this.

Isn't there a way to get the updated packages on 6.7? I don't have any box running the el6.8 ALPHA at this time but I will try to test it soon.

IMHO, since this was broken on 6.7 it should make its way into the 6.7.z erratas.

For my own curiosity, what was the fix and what component did it make it into?

Thanks,

Vincent

(In reply to Vincent S. Cojot from comment #15)
> Dear Tomas,
> Thanks for working on this.
> 
> Isn't there a way to get the updated packages on 6.7? I don't have any box
> running the el6.8 ALPHA at this time but I will try to test it soon.
> 
> IMHO, since this was broken on 6.7 it should make its way into the 6.7.z
> erratas.
> 
> For my own curiosity, what was the fix and what component did it make it
> into?
> 
> Thanks,
> 
> Vincent

The problem is that we rebased Xorg + whole graphics stack in rhel6.8 so it is not only about one rpm that could be delivered to you, in this case it is about ~200 pkgs. And this is also partially a reason why this can't be fixed in z-stream, the other reason is that rebases are prohibited in z-stream too.

The fix is in xorg-x11-server and in short the patch is about always implementing the backing store.

Anyway if you won't be able to test on 6.8 alpha/beta/whatever we are going to verify as sanity only, in case the issue is not fixed we will reopen or clone the bug for other release rather.

Does it make sense to you, would you agree?

Thanks and sorry for incovinience.
-Tom

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2016-0761.html