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From: Evgenii Shatokhin <eshatokhin@virtuozzo.com>
To: Nicolai Stange <nstange@suse.de>
Cc: Miroslav Benes <mbenes@suse.cz>,
	live-patching@vger.kernel.org, pmladek@suse.com
Subject: Re: Patching kthread functions
Date: Thu, 1 Oct 2020 16:18:24 +0300	[thread overview]
Message-ID: <c2a4f36b-d974-2fa6-65d6-0d058a8773d6@virtuozzo.com> (raw)
In-Reply-To: <87lfgqt8tt.fsf@suse.de>

Hi,

On 01.10.2020 15:43, Nicolai Stange wrote:
> Miroslav Benes <mbenes@suse.cz> writes:
> 
>> On Wed, 30 Sep 2020, Evgenii Shatokhin wrote:
> 
>>> Is that so? Are there any workarounds?
>>
>> Petr, do you remember the crazy workarounds we talked about? My head is
>> empty now. And I am sure, Nicolai could come up with something.
> 
> There might be some clever tricks ycou could play, but that depends on
> the diff you want to turn into a livepatch. For example, sometimes it's
> possible to livepatch a callee and make it trick the unpatchable caller
> into the desired behaviour.

In this particular case, we needed to add a kind of lock/unlock pair 
around the request processing part of the function. Unfortunately, there 
is no suitable callee there.
> 
> However, in your case it might be easier to simply kill the running
> kthread and start it again, e.g. from a ->post_patch() callback. Note
> that KLP's callbacks are a bit subtle though, at a minimum you'd
> probably also want to implement ->pre_unpatch() to roll everything back
> and perhaps also disable (->replace) downgrades by means of the klp_state API.

Interesting.

Something like: block submitting of new requests to the thread, wait for 
the old requests to be processed, kill the thread, then start it again, 
unblock the requests.

Thanks for the idea!
> 
> You can find some good docs on callbacks and klp_state at
> Documentation/livepatch/.
> 
> Thanks,
> 
> Nicolai
> 

Evgenii

  reply	other threads:[~2020-10-01 13:18 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30 15:44 Patching kthread functions Evgenii Shatokhin
2020-10-01 11:13 ` Miroslav Benes
2020-10-01 12:43   ` Nicolai Stange
2020-10-01 13:18     ` Evgenii Shatokhin [this message]
2020-10-01 13:12   ` Evgenii Shatokhin
2020-10-02 11:53     ` Miroslav Benes
2020-10-02 12:52       ` Evgenii Shatokhin
2020-10-02 13:06         ` Miroslav Benes
2020-10-01 14:46   ` Petr Mladek
2020-10-01 16:34     ` Evgenii Shatokhin

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