Messages in this thread | | | Date | Fri, 12 Aug 2005 18:18:33 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH] eliminte NMI entry/ exit code |
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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.
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