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    SubjectRe: [PATCH] kprobes: bugfix: try_module_get even if calling_mod is NULL
    Andrew Morton wrote:
    > I do not understand this description "Get probed module even if the
    > caller is in the kernel core code".
    > What bug is being fixed here? What is the kernel behaviour before and
    > after the patch?

    When someone called register_*probe() from kernel-core code(not from
    module) and that probes a kernel module, users can remove the probed
    module because kprobe doesn't increment reference counter of the module.
    (on the other hand, if the kernel-module calls register_*probe,
    kprobe increments refcount of the probed module.)

    Currently, we have no register_*probe() calling from kernel-core(except
    smoke-test, but the smoke-test doesn't probe module), so there is no
    real bugs. But the logic is wrong(or not fair) and it can causes a
    problem when someone might want to probe module from kernel.

    After this patch is applied, even if someone put register_*probe() call
    in the kernel-core code, it increments the reference counter of the
    probed module, and it prevents user to remove the module until stopping
    probing it.

    > Was the bug present in 2.6.27, 2.6.26 etc? Or was it a post-2.6.28
    > regression?

    Hmm, it might be an enhancement, because currently the kernel doesn't
    have real bugs.

    Thank you,

    Masami Hiramatsu

    Software Engineer
    Hitachi Computer Products (America) Inc.
    Software Solutions Division


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