[Bug 73282] New: [UXA] Rendering to screen-sized pbuffer affects actual screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=73282

          Priority: medium
            Bug ID: 73282
          Assignee: chris at chris-wilson.co.uk
           Summary: [UXA] Rendering to screen-sized pbuffer affects actual
                    screen
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: amonakov at gmail.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: Driver/intel
           Product: xorg

Created attachment 91488
  --> https://bugs.freedesktop.org/attachment.cgi?id=91488&action=edit
reproducer

The attached testcase fills a GLX Pbuffer with 0x80 gray.  It never creates a
window and thus should not affect the screen.

However, passing actual screen dimensions in arguments:

    ./a.out 1920 1080

causes the screen to become gray (as if the pbuffer's contents became visible).
 It also "works" to pass actual screen width and a fraction of actual height,
in which case the top fraction of the screen becomes gray.  Passing 4096 4096
in my case caused the test to be killed with "bus error".  The window manager
(xfwm4, fluxbox) becomes non-functional after triggering the issue.

This is reproducible on IVB with UXA, but not SNA.

Is UXA, um, somehow misallocating buffers for the pbuffer or swapping Mesa's
offscreen buffers onscreen?  I'd try to debug it myself, but I have no idea how
to approach it.  Please let me know if additional info is required.

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