[Bug 110251] Buffer age seems incorrect

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110251

            Bug ID: 110251
           Summary: Buffer age seems incorrect
           Product: Mesa
           Version: 19.0
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/Gallium/radeonsi
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: yshuiv7 at gmail.com
        QA Contact: dri-devel at lists.freedesktop.org

Created attachment 143784
  --> https://bugs.freedesktop.org/attachment.cgi?id=143784&action=edit
Demo of the problem

* Background

compton has the ability to do partial screen update. It will gather the damaged
regions from Xorg, query the buffer age using GLX, and then only update the
part of the screen that is damaged.

* Problem

When partial screen update is enabled, sometimes closed window is left on the
screen. 

Please see the attachment. 

In the clip, at first, I was repeatedly opening/closing Rofi, trying to
triggered bug (it does not reproduce consistently). After several attempts,
Rofi window is left on the screen after I closed it. Then, I moved my mouse
around to trigger updates of the window underneath.

However, if I capture a trace of this happening with apitrace, this problem
doesn't happen during the replay of the trace.

* Thoughts

Could it be mesa is returning the wrong buffer age of the back buffer?

* To reproduce

Build compton from the repo. Run it with `compton --config /dev/null
--use-damage --experimental-backends --backend glx`. Then try open/close window
several times.

* System info

Card: Radeon RX590
DDX: xf86-video-amdgpu
Mesa version: 19.0.0

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