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    SubjectRe: Calling current() from interrupt context
    On Mon, Oct 09, 2000 at 02:21:09AM +0100, Kenn Humborg wrote:
    > On Mon, Oct 09, 2000 at 02:20:27AM +0200, Andi Kleen wrote:
    > > 2.4 TCP code relies on current being valid in a softirq.
    > Well, then as long as Linux guarantees that there is always a
    > valid 'current task' on a CPU, then I can special-case the
    > called-from-interrupt case. The previous kernel stack pointer
    > is accessible from another processor register, so I can go in
    > there and pull it out and use it to calculate current.
    > Is it possible to get an interrupt during context switching,
    > for example? Or any other window during which there isn't
    > a valid current?

    You can get interrupts while running in user space and there
    isn't a valid current register. So you have to initialise it always
    in the interrupt entry. As long as you don't have to support SMP
    it is easy (just store current in a global variable and load it from there),
    with SMP it is more tricky but still possible, e.g. when you have
    some hidden register.

    > And what the hell does TCP need current for anyway?

    For a very hackish user context TCP implementation that probably should
    be cleaned up (but it is code freeze etc.etc.blabla.)

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