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SubjectRe: [PATCH] eliminte NMI entry/ exit code
Nick Piggin wrote:
> George Anzinger wrote:
>
>> The NMI entry and exit code fiddles with bits in the preempt count.
>> If an NMI happens while some other code is doing the same, bits will
>> be lost. This patch removes this modify code from the NMI path till
>> we can come up with something better.
>>
>
> Humour me for a minute here...
> NMI restores preempt_count back to its old value upon exit, right?
> So what does a race case look like?

Normal code NMI
fetch preempt_count
add <----- interrupt here add and store then subtract
and store, darn!
store preempt_count

Ok, no problem.

The problem is in the RT code when PREEMPT_DEBUG is on. The tests for
reasonable counts fail because of the rather undefined state when NMI
picks up the word. The failure is on the NMI side...
>

--
George Anzinger george@mvista.com
HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/
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