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    SubjectRe: Realtime Preemption, 2.6.12, Beginners Guide?
    Date
    On Thursday 07 Jul 2005 12:42, Ingo Molnar wrote:
    > * Alistair John Strachan <s0348365@sms.ed.ac.uk> wrote:
    > > > do you have DEBUG_STACKOVERFLOW and latency tracing still enabled? The
    > > > combination of those two options is pretty good at detecting stack
    > > > overflows. Also, you might want to enable CONFIG_4KSTACKS, that too
    > > > disturbs the stack layout enough so that the error message may make it
    > > > to the console.
    > >
    > > I already have 4KSTACKS on. Latency tracing is enabled, but
    > > STACKOVERFLOW isn't; I'll just reenable everything again until we fix
    > > this. Do you think if I removed the printk() line I might get some
    > > useful information, before it does the stack trace?
    >
    > usually such loops happen if the stack has been overflown and critical
    > information that lies on the bottom of the stack (struct thread_info) is
    > overwritten. Then we often cannot even perform simple printks. Stack
    > overflow debugging wont prevent the crash, but might give a better
    > traceback.

    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..

    --
    Cheers,
    Alistair.

    personal: alistair()devzero!co!uk
    university: s0348365()sms!ed!ac!uk
    student: CS/CSim Undergraduate
    contact: 1F2 55 South Clerk Street,
    Edinburgh. EH8 9PP.
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