Bug 101556

Summary:	[llvmpipe] crashes when GL context is created and a previous context was shared
Product:	Mesa	Reporter:	Florian Link <florianlink>
Component:	Mesa core	Assignee:	mesa-dev
Status:	RESOLVED FIXED	QA Contact:	mesa-dev
Severity:	normal
Priority:	medium
Version:	17.1
Hardware:	Other
OS:	All
Whiteboard:
i915 platform:		i915 features:
Attachments:	Screenshot of the crash, fence pointer is NULL.

Description Florian Link 2017-06-22 09:27:29 UTC

Created attachment 132131 [details]
Screenshot of the crash, fence pointer is NULL.

I built the current 17.1.3 release on Windows Visual Studio 2015 with LLVM 3.9 (and 4.0 as well).

When I start my Qt application, which creates some GL contexts, I get the crash that you can see in the attached images, when one of the contexts is created.

I tracked the crash down to the following commit (4 month ago):

https://github.com/mesa3d/mesa/commit/043883647acaee0b2c67c1c6b496404ebb4e8d67

As you can see in my screenshot, the fence pointer is NULL and it is not checked before calling a function that needs a valid fence pointer.

It seems to happen when wglMakeCurrent(NULL,NULL) is called by Qt and the context that was active before is a shared context, so the bad fence call happens.

Comment 1 Florian Link 2017-06-22 09:38:35 UTC

I reverted the commit from 

https://github.com/mesa3d/mesa/commit/043883647acaee0b2c67c1c6b496404ebb4e8d67

and then the crash is gone. The problem seems to be: 

stw_context.c: line 442:
         if (old_ctx->shared) {
            struct pipe_fence_handle *fence = NULL;
            old_ctx->st->flush(old_ctx->st,
                               ST_FLUSH_FRONT | ST_FLUSH_WAIT, &fence);
         }
         else {
            old_ctx->st->flush(old_ctx->st, ST_FLUSH_FRONT, NULL);
         }

if I change that back to just:

            old_ctx->st->flush(old_ctx->st, ST_FLUSH_FRONT, NULL);

then the crash is gone. Since the fence pointer points to NULL and stays NULL, the old_ctx->st->flush crashes.

Comment 2 Florian Link 2018-01-29 07:26:01 UTC

This is a duplicate of bug 102148, which has been fixed.

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