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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm1-V0.7.28-1
On Thu, 2004-11-18 at 13:35 +0100, Ingo Molnar wrote:
> i have released the -V0.7.28-1 Real-Time Preemption patch, which can be
> downloaded from the usual place:
> this should fix the lockup bug reported by Florian Schmidt.
> there's a generic PREEMPT bug in the upstream kernel: there exists a
> single-instruction race window in __flush_tlb(), if the kernel preempted
> exactly there in a lazy-TLB thread and certain other, rare scheduling
> and MM properties were true as well (a certain constellation of threads
> and lazy-TLB kernel threads occured), and the lazy-TLB task then got
> another user TLB to inherit, and switched to a task from which it
> inherited that new TLB, thus the wrong cr3 was loaded and inherited by
> this next, non-lazy-TLB next task; then (and only then) this scenario
> would typically manifest itself in the form of an infinite pagefault
> lockup occuring much after the fact, upon the next userspace access (to
> the joy of a totally baffled kernel developer). I suspect from the
> description you can guess how much fun it was to debug it =B-)
> the bug is even more rare in the generic kernel, because there most (but
> not all) TLB flush points are in a critical section.
> this fix could resolve some of the other 'my box just locked up'
> reports.


I've got one of those 'my box just locked up'. I can reproduce it with
0.7.25-1, 0.7.28-0 and 0.7.28-1 by starting the Jetty servlet container
with our inhouse java project under a Blackdown 1.4 jdk. Within a minute
the laptop just locks up: no mouse, no ping, console switching sysrq-t
or anything. The peculiar thing is that I was running 0.7.25-1 for two
or three days before and it was rocksolid. It was just when I started to
work with the jvm that things fell apart.

Any chance to get any interesting and helpful data in this setup ?


Christian Meder, email:

The Way-Seeking Mind of a tenzo is actualized
by rolling up your sleeves.

(Eihei Dogen Zenji)

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