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    SubjectRe: 2.6.18-rc6-mm1: GPF loop on early boot
    On Sunday 10 September 2006 13:57, Ingo Molnar wrote:
    > * Andi Kleen <> wrote:
    > > > This kernel won't boot here: it starts a GPFs loop on
    > > > early boot. I attached a screenshot of the first GPF
    > > > (pause_on_oops=120 helped).
    > >
    > > It's lockdep's fault. This patch should fix it:>
    > Well, it's also x86_64's fault: why does it call into a generic C
    > function (x86_64_start_kernel()) without having a full CPU state up and
    > running? i686 doesnt do it, never did.

    Actually i686 does now (since Jeremy's patches). The patch was for i386.
    x86_64 doesn't need it.

    But enough blame game. The "fault" in my original mail wasn't completely
    serious anyways ...

    > We had frequent breakages due to this property of the x86_64 arch code
    > (many more than this single incident with lockdep), tracing and all
    > sorts of other instrumentation (including earlier versions of lockdep)
    > was hit by it again and again.

    Well, just getting the new unwinder to work in lockdep was a nightmare
    too (most of the problems I had with that were on i386, not x86-64)
    Just look at the number of patches that were needed for it.

    > Basically, non-atomic setup of basic architecture state _is_ going to be
    > a nightmare, lockdep or not, especially if it uses common infrastructure
    > like 'current', spin_lock() or even something as simple as C functions.
    > (for example the stack-footprint tracer was once hit by this weakness of
    > the x86_64 code)

    I disagree with that. The nightmare is putting stuff that needs so much
    infrastructure into the most basic operations.

    > > Hackish patch to fix lockdep with PDA current
    > hm, this is ugly beyond words.

    Agreed it is :). But it was the quickest way to fix it.

    > Do you have a config i could try which
    > exhibits this problem? I'm sure there is a better solution.

    You need the latest x86_64 patch (or latest mm) and enable lockdep
    on i386. Possibly with some more interdependencies, but I hope not.

    I guess a cleaner way would to set the global variable that turns
    the tracing off during boot and then enable it when it starts making
    sense. Not 100% sure where that point is.

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      Last update: 2006-09-10 15:25    [W:0.032 / U:134.168 seconds]
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