Re: BUG: using smp_processor_id() during suspend with 2.6.25-rc8

Rafael J. Wysocki
2008-04-07T22:56:35Z

On Tuesday, 8 of April 2008, Jiri Kosina wrote:
> On Tue, 8 Apr 2008, Rafael J. Wysocki wrote:
>
> > > The mce resume is a sysdev.
> > > sysdevs were always supposed to run completely with interrupts off. If they
> > > don't anymore that's some kind of higher level resume code bug which you need
> > > to fix there, not hack around in the low level code.
> > They are executed with interrupts disabled, on one CPU.
>
> So, any idea why mce_resume() -> mce_init() -> debug_smp_processor_id()
> triggers the warning? Apparently preempt_count is zero, irqs_disabled()
> returns false, and cpumask_of_cpu() is not equal to current->cpus_allowed.
>
> So there clearly is a bug somewhere.

Yes, there is. Still, I wonder why doesn't everyone see it.

> > > Obviously turning on preemption anywhere around the machine check is
> > > fatal because it touches CPU state and if you reschedule you could
> > > switch to another CPU and change or access the wrong CPU's state.
> > FWIW, at the point when sysdevs are resumed we are single-threaded.
>
> Is that really relevant here? We still could be switched over to another
> CPU, and that would break things.

No, we couldn't, because the other CPUs are off at this point.

Thanks,
Rafael