Re: [Xen-devel] [PATCH 09/14] livepatch: Add per-function applied/reverted state tracking marker

[Julien Grall <julien.grall@xxxxxxx>]

Hi Pawel,

On 22/08/2019 12:02, Wieczorkiewicz, Pawel wrote:
> > On 22. Aug 2019, at 12:29, Julien Grall <julien.grall@xxxxxxx 
> > <mailto:julien.grall@xxxxxxx>> wrote:
> > On 21/08/2019 09:19, Pawel Wieczorkiewicz wrote:
> > More generally, I am not very comfortable to see panic() in the middle of the 
> > code. Could you explain why panic is the best solution over reverting the work?
> Yes. Production-ready hotpatches must not contain inconsistent hooks or 
> functions-to-be-applied/reverted.
> The goal here is to detect such hotpatches and fail hard immediately 
> highlighting the fact that such hotpatch
> is broken.
Aside the len = 0 that you are going to fix. How would this condition happen? 
Are you going to add code that will potentially trigger the panic?
> The inconsistent application of a hotpatch (some function applied, some reverted 
> while other left behined) leaves
> the system in a very bad state. I think the best what we could do here is 
> panic() to enable post-mortem analysis
> of what went wrong and avoid leaking such system into production.
Thank you for the explanation here (and on IRC). May I ask some documentation 
regarding the panic in at least commit message? Ideally, this would explain why 
the panic the most sensible solution.
Cheers,

--
Julien Grall

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