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SubjectRe: [RFC 0/9] mce recovery for Sandy Bridge server
On Tue, 2011-05-24 at 10:56 -0700, Tony Luck wrote:
> Dragging PeterZ to this thread, since we are now talking about scheduler.
> On Tue, May 24, 2011 at 10:33 AM, Borislav Petkov <> wrote:
> > On Tue, May 24, 2011 at 09:57:46AM -0700, Luck, Tony wrote:
> >> So can we talk about this part for a while before returning to the
> >> "how to report this" discussion?
> >>
> >> So here's the situation - we are in the NMI handler when we find from
> >> looking at the machine check bank registers that we have a recoverable
> >> error. We know the physical address, and we know the task (which might
> >> have been in user or kernel context). I can package that information
> >> into a perf/event ... but then how can I mark the current task as
> >> not-fit-for-execution?
> >
> > Maybe something like
> >
> > set_current_state(TASK_UNINTERRUPTIBLE);
> >
> > finish work in NMI context
> >
> > do remaining work in process context like sending appropriate signals
> > etc; finally:
> >
> > set_task_state(tsk, TASK_RUNNING)
> That looks pretty easy - are their any weird side effects that I should
> be worried about? My perf/event can't really include the "task" pointer
> (that sounds way too internal) - but I can provide the process id, so
> the "RAS daemon" that sees this event can look up the task to do that
> final set_task_state(tsk, TASK_RUNNING).
> Does this work in the threaded case? In the case where the task was in
> kernel context (but in a CONFIG_PREEMT=y kernel at some point
> where preemption is allowed)?

Right, so you can't do things like that from NMI context, but what perf
can do is raise a self-IPI and continue from IRQ context (question for
the HW folks, can there be cycles between the NMI iret and IRQ assert
from whatever context was before the NMI hit?)

From IRQ context we can wake threads, set TIF_flags etc. you can
basically do what SIGSTOP does and put the task in TASK_STOPPED state,
wake your handler thread and set TIF_NEED_RESCHED. Then the handler
thread will be scheduled depending on your handler's sched policy.

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