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From: Miroslav Benes <mbenes@suse.cz>
To: Evgenii Shatokhin <eshatokhin@virtuozzo.com>
Cc: live-patching@vger.kernel.org, pmladek@suse.com, nstange@suse.de
Subject: Re: Patching kthread functions
Date: Fri, 2 Oct 2020 13:53:21 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LSU.2.21.2010021339390.24950@pobox.suse.cz> (raw)
In-Reply-To: <05a9533b-4b12-d600-5307-1f4fadb44f2b@virtuozzo.com>


> >> The old function will continue running, right?
> > 
> > Correct. It will, however, call new functions.
> 
> Ah, I see.
> 
> So, I guess, our best bet would be to rewrite the thread function so that it
> contains just the event loop and calls other non-inline functions to actually
> process the requests. And, perhaps, - place klp_update_patch_state() before
> schedule().

Yes, that might be the way. klp_update_patch_state() might not be even 
needed. If the callees are live patched, the kthread would be migrated 
thanks to stack checking once a task leaves the callee.
 
> This will not help with this particular kernel version but could make it
> possible to live-patch the request-processing functions in the future kernel
> versions. The main thread function will remain unpatchable but it will call
> the patched functions once we switch the patch_state for the thread.

Yes. The only issue is if the intended fix changes the semantics which is 
incompatible between old and new functions (livepatch consistency model is 
LEAVE_PATCHED_SET, SWITCH_THREAD, see 
https://lore.kernel.org/lkml/20141107140458.GA21774@suse.cz/ for the 
explanation if interested).

Regards
Miroslav

  reply	other threads:[~2020-10-02 11:53 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
2020-10-01 13:12   ` Evgenii Shatokhin
2020-10-02 11:53     ` Miroslav Benes [this message]
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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