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SubjectRe: Realtime Preemption, 2.6.12, Beginners Guide?

* Alistair John Strachan <> wrote:

> Well, just to let others who have this problem know, it's clear that
> Ingo's rt-preempt patches increase stack pressure on systems (like
> mine) where stack is borderline under 4K by default.
> If you disable CONFIG_4KSTACKS the stack overflows seem to disappear.
> As a result, until we isolate the problem, it'd probably be better if
> Ingo maintained an 8K stacks option in the rt-preempt patches assuming
> Adrian Bunk's "kill !4KSTACKS" patch gets into mainline..

Ok. Could you try to debug this some more? In the -51-17 patch i've
implemented a new stack-overflow debugging feature: 'stack footprint
maximum searching'. It is automatically active if you have
track and (if it can be done safely) print out maximum stack usage sites
immediately. Hopefully this results in better stackdumps. It should
print similar traces:

| new stack-footprint maximum: smartd/1747, 1768 bytes.
[<c013c1b6>] check_raw_flags+0xb/0x55 (8)
[<c013ebeb>] sub_preempt_count+0x1a/0x1c (8)
[<c013cb28>] __mcount+0x6a/0x91 (28)
[<c013c3ff>] irqs_disabled+0x8/0x19 (16)
[<c013c7b5>] ____trace+0x9e/0x208 (4)
[<c01142d8>] mcount+0x14/0x18 (24)
[<c013c3ff>] irqs_disabled+0x8/0x19 (20)
[<c013c7b5>] ____trace+0x9e/0x208 (8)
[<c013f145>] trace_stop_sched_switched+0x40/0x17d (8)

i've written a separate, hopefully more robust stack-dumper which is
used for the above traces. Perhaps in your overflow case it results in
something usable.

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