Messages in this thread | | | From | Andi Kleen <> | Subject | Re: 2.6.18-rc6-mm1: GPF loop on early boot | Date | Sun, 10 Sep 2006 13:34:34 +0200 |
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On Sunday 10 September 2006 13:57, Ingo Molnar wrote: > * Andi Kleen <ak@suse.de> 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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