Re: Random crashes with 2.6.27-rc3 on PPC

On Sunday 24 August 2008 00:52:49 Benjamin Herrenschmidt wrote:

On Sat, 2008-08-23 at 16:10 +0200, Michael Buesch wrote:

quoted

I am seeing random kernel and userland application
crashes on a Powerbook running a 2.6.27-rc3 based kernel (wireless-testing.git).

The crashes did recently appear. It might be the case that they were
introduced with the merge of 2.6.27-rc1 into wireless-testing.
I'm not sure on that one, however. Just a guess. I still need to
do more testing (also on vanilla upstream kernels).

The crashes are completely random and they look like bad hardware.
However I cannot reproduce on 2.6.25.9 (That's a kernel I still had
installed, so I tried that one). So it most likely is _not_ caused
by faulty hardware.

The crashes are hard to reproduce, and happen about every 20 minutes
when compiling a kernel tree. (gcc segfaults). Sometimes the kernel
oopses in random places with pointer dereference faults.

Is this a known issue?
I'm going to bisect this one, but it will take a lot of time, as reproducing
takes about 20 minutes. So that's about an hour for one test round.

The kernel configuration is the following:

Random guess:

CONFIG_FRAME_POINTER=y
CONFIG_SCHED_NO_NO_OMIT_FRAME_POINTER=y

Note sure what those together do, check if you have any file compiled
with -fno-omit-frame-pointer and if you do, try to change things so
that you don't ... we found some miscompiles when that is set, exposed
by FTRACE typically (which you don't have enabled) but possibly by other
things.

Ok, thanks for the suggestion.
I could reproduce the crash with 2.6.26, so this is not a regression between
2.6.26 and 2.6.27-rcX.
I'm currently running longer tests on 2.6.25 again to make sure it really
isn't hardware related.


NO_NO_OMIT is a brain screwer, btw :)

-- 
Greetings Michael.