Re: 2.6.7-rc1-bk: SMT scheduler bug / crashes on kernel boot

[Nick Piggin]

Anton Altaparmakov wrote:
> On Wed, 2004-05-26 at 12:13, Nick Piggin wrote:
>
> > Anton Altaparmakov wrote:
> >
> > > Hi,
> > >
> > > Kernel 2.6.7-rc1-bk crashes on boot with a NULL pointer dereference. 
> > > The kernel is running under VMware if that matters but I don't think it
> > > should.  It was working fine with 2.6.6-rc3-bk kernels.
> > >
> > > I am afraid the only way I could capture the crash was to capture the
> > > vmware screen into a PNG image which is attached.  Maybe I need to setup
> > > some OCR software for in the future...  (-;
> > >
> > > The system running VMware is a P4 2.6Hz with Hyper threading enabled and
> > > /proc/cpuinfo shows two cpus:
> >
> > OK, thanks for that. It would be quite helpful if you edit
> > kernel/sched.c and turn the line #undef SCHED_DOMAIN_DEBUG into
> > #define SCHED_DOMAIN_DEBUG, then compile a kernel with debugging
> > info enabled.
>
>
> Looking at kernel/sched.c it already says #define, not #undef!

Oops, yes.

[snip]

> So the dereferencing of one of the two fails.  Considering the offset is
> 0x18 in the NULL dereference it must be the (p)->prio that causes the
> oops and hence p must be NULL.  I will leave you to figure out what that
> means...

Nice detective work.

It tried to dereference a NULL idle thread I'd say.
ie. the CPU hasn't been set up. Please try Ingo's patch.
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