netdev - RE: [RFC net-next] xfrm: refactory to avoid state tasklet scheduling errors

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Date:	Wed, 15 Jul 2015 14:33:28 +0000
From:	"Cantavenera, Giuseppe (EXT-Other - DE/Ulm)" 
	<giuseppe.cantavenera.ext@...ia.com>
To:	"ext Du, Fan" <fan.du@...el.com>,
	Giuseppe Cantavenera <giuseppe.cantavenera@...om.it>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	Steffen Klassert <steffen.klassert@...unet.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>,
	"Glavinic-Pecotic, Matija (EXT-Other - DE/Ulm)" 
	<matija.glavinic-pecotic.ext@...ia.com>,
	"Faustini, Nicholas (EXT-Other - DE/Ulm)" 
	<nicholas.faustini.ext@...ia.com>
Subject: RE: [RFC net-next] xfrm: refactory to avoid state tasklet
 scheduling errors



>-----Original Message-----
>From: ext Du, Fan [mailto:fan.du@...el.com]
>Sent: Tuesday, July 14, 2015 9:53 AM
>To: Giuseppe Cantavenera; netdev@...r.kernel.org
>Cc: Steffen Klassert; David S. Miller; Sverdlin, Alexander (Nokia -
>DE/Ulm); Glavinic-Pecotic, Matija (EXT-Other - DE/Ulm); Cantavenera,
>Giuseppe (EXT-Other - DE/Ulm); Faustini, Nicholas (EXT-Other - DE/Ulm);
>Du, Fan
>Subject: RE: [RFC net-next] xfrm: refactory to avoid state tasklet
>scheduling errors
>
>
>
>>-----Original Message-----
>>From: Giuseppe Cantavenera [mailto:giuseppe.cantavenera@...om.it]
>>Sent: Tuesday, July 7, 2015 3:43 PM
>>To: netdev@...r.kernel.org
>>Cc: Giuseppe Cantavenera; Steffen Klassert; David S. Miller; Du, Fan;
>Alexander
>>Sverdlin; Matija Glavinic Pecotic; Giuseppe Cantavenera; Nicholas
>Faustini
>>Subject: [RFC net-next] xfrm: refactory to avoid state tasklet
>scheduling errors
>>Hello,
>>
>>we also meet the same bug Fan Du did a while ago.
>>Two solutions were proposed in the past:
>>either forcibly mark as expired all of the keys every time the clock is
>set,
>>or replace the existing timers with relative ones.
>>
>>The former would introduce unexpected behaviour
>>(the keys would keep expiring when they shouldn't) and does not address
>the
>>real problem: THE COUPLING between the SA scheduling and the wall
>timer.
>>Actually it introduces even more of that.
>>
>>The latter is robust, extremly lightweight and maintanable, and
>preserves the
>>expected behaviour, that's why we preferred it.
>>
>>Any feedback or any other idea is greatly appreciated.
>
>Thanks for keep working this issue as I did 2 years ago.
>
>Objection against the original approach from the maintainers is that it
>complicates
>the logic to the degree which involving extra maintenance effort, that
>is the effort
>it's not worthwhile against the trouble it might introduce in the
>future.
>
>Another approach you can try is using monotonic boot time(counting in
>suspend time also)
>to mark the life time of SA, then the timer handler logic will be quite
>easier and smaller
>than now, sure it will be robust naturally. The cost is that SA lifetime
>displaying by setkey
>and SA migration has to be taken care of as SA life time is boot time
>now, not the wall time.


Hi Fan Du, 
 Thanks for your feedback.

It can probably work that way.
I think we can wait if someone else has any further comments,
then maybe try to see how it works.

Thanks,
Giuseppe



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