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    SubjectRe: [PATCH 1/5] ftrace: use module notifier for function tracer
    On Sun, 19 Apr 2009, Rusty Russell wrote:

    > I think you need to do something else in general. Share the module_mutex for
    > the ftrace code? The ksplice guys have a similar issue, so maybe we should
    > generalize this into a "kernel_text" mutex?

    Yes, a kernel_text mutex is on my list of things to propose once Ksplice
    gets merged.

    There are at present several systems that modify the kernel text after a
    machine is booted (e.g. dynamic ftrace and toggling of smp_locks when
    hotplugging a cpu). Currently, they avoid stepping on each other by only
    making changes inside stop_machine.

    However, Ksplice does its run-pre matching checks outside stop_machine,
    and Ksplice needs a way to prevent e.g. dynamic ftrace from changing the
    code out from under it between those checks and actually applying the
    patches [1]. A kernel_text mutex would be a reasonable solution to this
    problem.

    -Tim Abbott

    [1] At present this isn't a real problem because Ksplice and ftrace
    conflict with each other for unrelated reasons.


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