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    SubjectRe: [RFC] [PATCH 0/7] UBP, XOL and Uprobes [ Summary of Comments and actions to be taken ]
    Here is a summary of the Comments and actions that need to be taken for
    the current uprobes patchset. Please let me know if I missed or
    misunderstood any of your comments.

    1. Uprobes depends on trap signal.
    Uprobes depends on trap signal rather than hooking to the global
    die notifier. It was suggested that we hook to the global die notifier.

    In the next version of patches, Uprobes will use the global die
    notifier and look at the per-task count of the probes in use to
    see if it has to be consumed.

    However this would reduce the ability of uprobe handlers to
    sleep. Since we are dealing with userspace, sleeping in handlers
    would have been a good feature. We are looking at ways to get
    around this limitation.


    2. XOL vma vs Emulation vs Single Stepping Inline vs using Protection
    Rings.
    XOL VMA is an additional process address vma. This is
    opposition to add an additional vma without user actually
    requesting for the same.

    XOL vma and single stepping inline are the two architecture
    independent implementations. While other implementations are
    more architecture specific. Single stepping inline wouldnt go
    well with multithreaded process.

    Even though XOL vma has its own issues, we will go with it since
    other implementations seem to have more complications.

    we would look forward to implementing boosters later.
    Later on, if we come across another techniques with lesser
    side-effects than the XOL vma, we would switch to using them.


    3. Current Uprobes looks at process life times and not vma lifetimes.
    Also it needs threads to quiesce when inserting and removing
    breakpoints.

    Current uprobes was quiesing threads of a process before
    insertion and deletion. This resulted in uprobes having to track
    process lifetimes. An alternative method to track vma lifetimes
    was suggested.

    Next version would update the copy of the page and flip the
    pagetables as suggested by Peter. Hence it would no more depend on
    threads quiescing.

    However this would need hooks in munmap/rmap so that uprobes can
    remove breakpoints that are placed in that vma.

    This would also mean removing the rcu_deference we were using.

    4. Move the ftrace plugin to use trace events.

    Since ftrace plugins are relegated to obsolescence, it was
    suggested we use trace events which would have much wider scope.

    Next version will use trace events.

    5. rename UBP to user_bkpt

    6. updating the authors for all files that are getting added.

    I shall work towards v2 of uprobes and send across the patches at the
    earliest.

    --
    Thanks and Regards
    Srikar


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