Re: [RFC PATCH 0/2] kpatch: dynamic kernel patching
[Posted May 6, 2014 by corbet]
| From: |
| Josh Poimboeuf <jpoimboe-AT-redhat.com> |
| To: |
| Ingo Molnar <mingo-AT-kernel.org> |
| Subject: |
| Re: [RFC PATCH 0/2] kpatch: dynamic kernel patching |
| Date: |
| Mon, 5 May 2014 08:26:38 -0500 |
| Message-ID: |
| <20140505132638.GA14432@treble.redhat.com> |
| Cc: |
| Seth Jennings <sjenning-AT-redhat.com>, Masami Hiramatsu <masami.hiramatsu.pt-AT-hitachi.com>, Steven Rostedt <rostedt-AT-goodmis.org>, Frederic Weisbecker <fweisbec-AT-gmail.com>, Ingo Molnar <mingo-AT-redhat.com>, Jiri Slaby <jslaby-AT-suse.cz>, linux-kernel-AT-vger.kernel.org, Peter Zijlstra <a.p.zijlstra-AT-chello.nl>, Andrew Morton <akpm-AT-linux-foundation.org>, Linus Torvalds <torvalds-AT-linux-foundation.org>, Thomas Gleixner <tglx-AT-linutronix.de> |
| Archive‑link: | |
Article |
On Mon, May 05, 2014 at 10:55:37AM +0200, Ingo Molnar wrote:
>
> * Josh Poimboeuf <jpoimboe@redhat.com> 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.
I had considered doing this before, but the problem I found is that many
kernel threads are unfreezable. So we wouldn't be able to check whether
its safe to replace any functions in use by those kernel threads.
--
Josh
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