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    SubjectRe: workqueues and percpu (was: [PATCH] dm: remake of the verity target)
    Hello,

    On Fri, Mar 09, 2012 at 01:15:12PM -0800, Mandeep Singh Baines wrote:
    > In this case, I need the per-cpu data for the duration of calculating
    > a cryptographics hash on a 4K page of data. That's a long time to disable
    > pre-emption.

    How long are we talking about? Tens of microsecs, tens of millisecs?

    > I could fix the bug temporarily by adding get/put for the per_cpu data
    > but would that be acceptable? I'm not sure what the OK limit is for how
    > long one can disable preemption. An alternative fix would be not allow
    > CONFIG_VERITY when CONFIG_HOTPLUG_CPU. Once workqueues are fixed, I could
    > remove that restriction.

    I think the right thing to do for now is to add cpu hotplug notifier
    and do flush_work_sync() on the work item. We can later move that
    logic into workqueue and remove it from crypto.

    Thanks.

    --
    tejun


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