[PROBLEM] Soft lockup on Linux 2.6.27, 2 patches, Cell/PPC64

[Geert Uytterhoeven]

On Wed, 15 Oct 2008, Benjamin Herrenschmidt wrote:
> > > Well, at the time of the sample, the other CPU indeed -seems- to be in
> > > an IRQ disabled section yes. 
> > 
> > This is not really a sample. The hardirqs enable/disable is actually tracked
> > using the TRACE_{EN,DIS}ABLE_INTS macros.
> 
> That's what I meant. IE. the hardirq state was updated by the stuck CPU
> but sampled by the non-stuck one. ie. the non-stuck one could have
> sampled a transcient value where it happened to have hard irq
> disabled...

These states are per_cpu.

> > Aha, none of the PPC interrupt handlers actually us TRACE_ENABLE_INTS (they do
> > use TRACE_DISABLE_INTS). So that's why it thinks decrementer_common disabled
> > interrupts, without enabling them again...
> 
> Well, they aren't supposed to enable IRQs if they were disabled...

They do call TRACE_DISABLE_INTS, which records the interrupt being disabled.
So this makes the actual state recording useless...

With kind regards,

Geert Uytterhoeven
Software Architect

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