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Re: [RFC PATCH 0/2] kpatch: dynamic kernel patching

From:  Ingo Molnar <>
To:  Josh Poimboeuf <>
Subject:  Re: [RFC PATCH 0/2] kpatch: dynamic kernel patching
Date:  Mon, 5 May 2014 10:55:37 +0200
Message-ID:  <>
Cc:  Seth Jennings <>, Masami Hiramatsu <>, Steven Rostedt <>, Frederic Weisbecker <>, Ingo Molnar <>, Jiri Slaby <>,, Peter Zijlstra <>, Andrew Morton <>, Linus Torvalds <>, Thomas Gleixner <>
Archive-link:  Article

* Josh Poimboeuf <> wrote:

> [...]
> kpatch checks the backtraces of all tasks in stop_machine() to 
> ensure that no instances of the old function are running when the 
> new function is applied.  I think the biggest downside of this 
> approach is that stop_machine() has to idle all other CPUs during 
> the patching process, so it inserts a small amount of latency (a few 
> ms on an idle system).

When live patching the kernel, how about achieving an even 'cleaner' 
state for all tasks in the system: to freeze all tasks, as the suspend 
and hibernation code (and kexec) does, via freeze_processes()?

That means no tasks in the system have any real kernel execution 
state, and there's also no problem with long-sleeping tasks, as 
freeze_processes() is supposed to be fast as well.

I.e. go for the most conservative live patching state first, and relax 
it only once the initial model is upstream and is working robustly.


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