Messages in this thread | | | Subject | Re: [RFC] [patch 4/6 -rt] powerpc 2.6.20-rt8: fix a runtime warnings for xmon | From | Benjamin Herrenschmidt <> | Date | Wed, 07 Mar 2007 11:10:59 +0100 |
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On Wed, 2007-03-07 at 10:16 +0100, Ingo Molnar wrote: > * Tsutomu OWA <tsutomu.owa@toshiba.co.jp> wrote: > > > @@ -342,6 +342,7 @@ static int xmon_core(struct pt_regs *reg > > > > msr = mfmsr(); > > mtmsr(msr & ~MSR_EE); /* disable interrupts */ > > + preempt_disable(); > > i'm not an xmon expert, but maybe it might make more sense to first > disable preemption, then interrupts - otherwise you could be preempted > right after having disabled these interrupts (and be scheduled to > another CPU, etc.). What is the difference between local_irq_save() and > the above 'disable interrupts' sequence? If it's not the same and > xmon_core() relied on having hardirqs disabled then it might make sense > to do a local_irq_save() there, instead of a preempt_disable().
powerpc 64 bits nowadays does lazy HW masking, so local_irq_disable() will not actually switch MSR_EE off. However, xmon needs that to happen (though we have a nicer accessor to do it, I suspect some bitrot need fixing in there, possibly already fixed in .21)
I agree that preempt_disable() should be put before the MSR tweaking though.
Ben.
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