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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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