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SubjectRe: [PATCH v14 08/11] livepatch: Remove Nop structures when unused
On Thu, Nov 29, 2018 at 10:44:28AM +0100, Petr Mladek wrote:
> Replaced patches are removed from the stack when the transition is
> finished. It means that Nop structures will never be needed again
> and can be removed. Why should we care?
>
> + Nop structures make false feeling that the function is patched
^^^^^^^^^^^^^^^^^^
re-wording suggestion: "give the impression"

> even though the ftrace handler has no effect.
>
> + Ftrace handlers are not completely for free. They cause slowdown that
^^^^^^^^
re-wording suggesions: "free" or "do not come for free"

> might be visible in some workloads. The ftrace-related slowdown might
> actually be the reason why the function is not longer patched in
^^^^^^^^^^
s/not longer/no longer

> the new cumulative patch. One would expect that cumulative patch
> would allow to solve these problems as well.
^^^^^^^^^^^^^^
re-wording suggestion: "help solve"

>
> + Cumulative patches are supposed to replace any earlier version of
> the patch. The amount of NOPs depends on which version was replaced.
> This multiplies the amount of scenarios that might happen.
>
> One might say that NOPs are innocent. But there are even optimized
> NOP instructions for different processor, for example, see
^^^^^^^^^
s/processor/processors

> arch/x86/kernel/alternative.c. And klp_ftrace_handler() is much
> more complicated.
>
> + It sounds natural to clean up a mess that is not longer needed.
^^^^^^^^^^
s/not longer/no longer

> It could only be worse if we do not do it.
>
> This patch allows to unpatch and free the dynamic structures independently
> when the transition finishes.
>
> The free part is a bit tricky because kobject free callbacks are called
> asynchronously. We could not wait for them easily. Fortunately, we do
> not have to. Any further access can be avoided by removing them from
> the dynamic lists.
>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> ---

Acked-by: Joe Lawrence <joe.lawrence@redhat.com>

-- Joe

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