On Fri, 12 Aug 2005, 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.
Why?
Even if an NMI happens in the middle of a read-modify-write sequence that
is critical, the NMI exit is supposed to undo whatever it was that the NMI
entry did, so the preempt counters are "safe" wrt NMI: they may change,
but they always change back by the time anybody cares.
This, btw, is something we depend on wrt _normal_ interrupts too. It's why
people can read/modify/write preempt count without having to disable
interrupts.
Linus
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