On 2018-07-18 12:28:48 [+0200], Mike Galbraith wrote:

quoted

Okay, so you did not test this because you can't compile.

Nope, the running kernel, the one that is doing the segfaulting etc,
has the patches applied.

It is exhibiting that symptom because those patches do not cure this
symptom, one which I verified to be present in virgin 4.14-rt as well. 
The pseudo-patch I sent, disabling preemption where it is assumed to be
disabled instead, does cure it.  With preemption so disabled, I can
beat on affected kernels (>=4.14-rt) as long as I like.

ah. so gcc shows the problem instead gcc explodes with the patch
applied. Okay. Let me stare at this a little more?

This particular 48 core Cavium is very slow, maybe that makes it easier
to reproduce, dunno.  According to pipe-test, the thing is essentially
a dozen RPi super-glued together.  pipe-test pinned to a single core
can only context switch at ~40KHz with PREEMPT_RT, or ~90 with
NOPREEMPT, comparable to measurement done in real deal RPi.

	-Mike

Sebastian