Seen in bug 1624250 comment 3:

This bug is for crash report bp-68978ac6-e40a-478f-a511-27f1d0200324.

internal error: entered unreachable code

Top 10 frames of crashing thread:

0 xul.dll RustMozCrash mozglue/static/rust/wrappers.cpp:16
1 xul.dll mozglue_static::panic_hook mozglue/static/rust/lib.rs:89
2 xul.dll core::ops::function::Fn::call<fn ../f3e1a954d2ead4e2fc197c7da7d71e6c61bad196/src/libcore/ops/function.rs:232
3 xul.dll std::panicking::rust_panic_with_hook ../f3e1a954d2ead4e2fc197c7da7d71e6c61bad196//src/libstd/panicking.rs:475
4 xul.dll std::panicking::begin_panic<str*> ../f3e1a954d2ead4e2fc197c7da7d71e6c61bad196/src/libstd/panicking.rs:404
5 xul.dll webrender::renderer::Renderer::draw_frame gfx/wr/webrender/src/renderer.rs
6 xul.dll webrender::renderer::Renderer::render_impl gfx/wr/webrender/src/renderer.rs:3274
7 xul.dll webrender::renderer::Renderer::render gfx/wr/webrender/src/renderer.rs:3052
8 xul.dll webrender_bindings::bindings::wr_renderer_render gfx/webrender_bindings/src/bindings.rs:603
9 xul.dll mozilla::wr::RendererOGL::UpdateAndRender gfx/webrender_bindings/RendererOGL.cpp:154

I assume this is this line here: https://hg.mozilla.org/mozilla-central/annotate/9b338268ce36c3387eb27c15f082e8c8f421112c/gfx/wr/webrender/src/renderer.rs#l5730

If it's that line of code, it might suggest that there is a bug in the code that handles a switch from native compositor <-> draw compositor, which I think occurs when taking screenshots in the profiler? Do we have any bug repro steps? Does that sound right to you, Sotaro?

Yea, it seems that problem happened during switch from native compositor <-> draw compositor. I am going to check if it is reproducible.

I could reproduce the problem.

The crash happened by reusing old Tile's descriptor SurfaceTextureDescriptor::Native. SurfaceTextureDescriptor::Native could not be used when wr native compositor is disabled.

https://hg.mozilla.org/mozilla-central/rev/95ddb3213aec

Comment on attachment 9137388 [details]
Bug 1624817 - Fix Tile invalidation during disabling WR native compositor

Beta/Release Uplift Approval Request

• User impact if declined: CPU process could crash during profiling with screenshots and WebRender native compositor on. Though taking screenshot during profiling is off by default on Firefox 75.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: none
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): It is simple fix that address Tile invalidation.
• String changes made/needed: none

Comment on attachment 9137388 [details]
Bug 1624817 - Fix Tile invalidation during disabling WR native compositor

Too late for 75, sorry.

Also given this is disabled by default and very low volume on beta it doesn't seem like a must-have.