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    SubjectRe: BUG: using smp_processor_id() during suspend with 2.6.25-rc8
    On Tue, Apr 08, 2008 at 12:29:30AM +0200, Rafael J. Wysocki wrote:
    > On Tuesday, 8 of April 2008, Andi Kleen wrote:
    > > On Tue, Apr 08, 2008 at 12:11:17AM +0200, Jiri Kosina wrote:
    > > > On Tue, 8 Apr 2008, Andi Kleen wrote:
    > > >
    > > > > > I know. However preempt_count is a little bit inconsistent in such cases
    > > > > > though.
    > > > > And? interrupts off beats preempt count anyways. Why did you write the
    > > > > patch? Was there a (incorrect) warning triggered?
    > > >
    > > > Reported at http://lkml.org/lkml/2008/4/7/130
    > > >
    > > > BTW is also mce_init() (called from mce_resume()) guaranteed to run with
    > > > IRQs off?
    > >
    > > [cc rafael]
    > >
    > > 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.

    Well then someone enables them incorrectly, see the report above.

    >
    > > If it does that it likely broke more code too.
    > >
    > > 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.

    You mean single CPUed? Even a single thread could switch to another CPU.

    -Andi


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