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    SubjectRe: [Xen-devel] [PATCH 05/27] xen, cpu hotplug: Don't call cpu_bringup() in xen_play_dead()
    >>> On 01.06.12 at 17:13, "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
    wrote:
    > On 06/01/2012 06:29 PM, Jan Beulich wrote:
    >
    >>>>> On 01.06.12 at 11:11, "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
    >> wrote:
    >>> xen_play_dead calls cpu_bringup() which looks weird, because xen_play_dead()
    >>> is invoked in the cpu down path, whereas cpu_bringup() (as the name
    >>> suggests) is useful in the cpu bringup path.
    >>
    >> This might not be correct - the code as it is without this change is
    >> safe even when the vCPU gets onlined back later by an external
    >> entity (e.g. the Xen tool stack), and it would in that case resume
    >> at the return point of the VCPUOP_down hypercall. That might
    >> be a heritage from the original XenoLinux tree though, and be
    >> meaningless in pv-ops context - Jeremy, Konrad?
    >>
    >> Possibly it was bogus/unused even in that original tree - Keir?
    >>
    >
    >
    > Thanks for your comments Jan!
    >
    > In case this change is wrong, the other method I had in mind was to call
    > cpu_bringup_and_idle() in xen_play_dead(). (Even ARM does something similar,
    > in the sense that it runs the cpu bringup code including cpu_idle(), in the
    > cpu offline path, namely the cpu_die() function). Would that approach work
    > for xen as well? If yes, then we wouldn't have any issues to convert xen to
    > generic code.

    No, that wouldn't work either afaict - the function is expected
    to return.

    Jan



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