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    SubjectRe: [RFC][PATCH] kprobes: Add separate preempt_disabling for kprobes
    [ Added some of the affected maintainers, left off David Howells and
    David Miller due to LKML Cc limit ]

    On Fri, 2011-07-01 at 10:22 +0900, Masami Hiramatsu wrote:
    > (2011/07/01 6:56), Peter Zijlstra wrote:
    > > On Thu, 2011-06-30 at 11:51 -0400, Steven Rostedt wrote:
    > >>
    > >> To solve this, I've added a per_cpu variable called
    > >> kprobe_preempt_disabled, that is set by the kprobe code. If it is set,
    > >> the preempt_schedule() will not preempt the code.
    > Sorry for replying so late :(

    Heh, who can blame you? Timezones make open source development a
    wait-and-see affair.

    > > Damn this is ugly. Can we step back and see if we can make the
    > > requirement for kprobe to disable preemption go away?
    > As I replied right now, I think we can just eliminate that
    > disabling preemption code. At least we'd better try it.
    > I agree with you, introducing this kind of complexity
    > just for kprobes is not what I want. :(

    Note, I did clean up this patch, so it is not as fugly.

    > > Why does it have to do that anyway? Isn't it keeping enough per-task
    > > state to allow preemption over the single step?
    > preemption itself must not happen on single stepping, but it seems
    > impossible to do heavy context switching with setting TF bit...

    Yeah, if all archs single step with interrupts disabled, then we should
    be fine with removing preemption.

    -- Steve

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