Comment 57 for bug 1813657

@P.D. That's surprising. In that case, it means the offending commit is "325f8e18c8ac drm/i915/ringbuffer: Delay after EMIT_INVALIDATE for gen4/gen5". I was expecting the offending commit to be "d8370b8fbadf drm/i915/execlists: Force write serialisation into context image vs execution" because that appears to have been identified upstream as causing a regression with symptoms similar to what you're experiencing (the regression has upstream commit ID 987abd5c62f9 and the fix for it is https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cf66b8a0ba142fbd1bf10ac8f3ae92d1b0cb7b8f )

I had built a kernel with the upstream fix for you to test and was expecting it would fix your problem. Do you mind trying it anyway to confirm that it does NOT fix your problem?

That kernel is built from commit:

619b700ded65 drm/i915/execlists: Apply a full mb before execution for Braswell

and can be found at:

https://kernel.ubuntu.com/~kmously/1813657/kernel-kmously-619b700-ouqM/

Thanks.