[Bug 78769] New: i965: glGetGraphicsResetStatusARB always returns *RESET* status and never NO_ERROR

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78769

          Priority: medium
            Bug ID: 78769
          Assignee: idr at freedesktop.org
           Summary: i965: glGetGraphicsResetStatusARB always returns
                    *RESET* status and never NO_ERROR
        QA Contact: intel-3d-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: pavel.e.popov at intel.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: 10.1
         Component: Drivers/DRI/i965
           Product: Mesa

Created attachment 99138
  --> https://bugs.freedesktop.org/attachment.cgi?id=99138&action=edit
Initial patch to resolve this issue

Overview:
=========
The glGetGraphicsResetStatusARB from ARB_robustness extension always returns
GUILTY_CONTEXT_RESET_ARB and never returns NO_ERROR for guilty context with
LOSE_CONTEXT_ON_RESET_ARB strategy.
This is because Mesa returns GUILTY_CONTEXT_RESET_ARB if batch_active !=0
whereas kernel driver never reset batch_active and this variable always > 0 for
guilty context.
The same behaviour also can be observed for batch_pending and
INNOCENT_CONTEXT_RESET_ARB.

But spec says the following
(http://www.opengl.org/registry/specs/ARB/robustness.txt):

  If a reset status other than NO_ERROR is returned and subsequent
  calls return NO_ERROR, the context reset was encountered and
  completed. If a reset status is repeatedly returned, the context may
  be in the process of resetting.

  8. How should the application react to a reset context event?
  RESOLVED: For this extension, the application is expected to query
  the reset status until NO_ERROR is returned. If a reset is encountered,
  at least one *RESET* status will be returned. Once NO_ERROR is
  encountered, the application can safely destroy the old context and
  create a new one.


Reproducer:
===========
1. Create context with GL_LOSE_CONTEXT_ON_RESET_ARB strategy using
glXCreateContextAttribsARB().
2. Provoke hardware reset. For example using infinite shader.
3. Call glGetGraphicsResetStatusARB() in a loop.
4. Make sure that this function always returns GUILTY_CONTEXT_RESET_ARB. It's a
wrong behavior.


Solution:
=========
The main problem is the context may be in the process of resetting and in this
case a reset status should be repeatedly returned. But looks like the kernel
driver returns nonzero active/pending only if the context reset has already
been encountered and completed.
For this reason the *RESET* status cannot be repeatedly returned and should be
returned only once.

The reset_count and brw->reset_count variables can be used to control that
glGetGraphicsResetStatusARB returns *RESET* status only once for each context.
Note the i915 triggers reset_count twice which allows to return correct reset
count immediately after active/pending have been incremented.

The patch is attached.

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