netdev - RE: Help needed - Kernel lockup while running ipsec

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Message-ID: <DB7PR04MB4620C6E770C97AB14A04A1D98BAB0@DB7PR04MB4620.eurprd04.prod.outlook.com>
Date:   Tue, 20 Aug 2019 09:10:45 +0000
From:   Vakul Garg <vakul.garg@....com>
To:     Florian Westphal <fw@...len.de>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: Help needed - Kernel lockup while running ipsec

Thanks for your response.


> -----Original Message-----
> From: Florian Westphal <fw@...len.de>
> Sent: Monday, August 19, 2019 11:08 PM
> To: Vakul Garg <vakul.garg@....com>
> Cc: netdev@...r.kernel.org
> Subject: Re: Help needed - Kernel lockup while running ipsec
> 
> Vakul Garg <vakul.garg@....com> wrote:
> > Hi
> >
> > With kernel 4.14.122, I am getting a kernel softlockup while running single
> static ipsec tunnel.
> > The problem reproduces mostly after running 8-10 hours of ipsec encap
> test (on my dual core arm board).
> >
> > I found that in function xfrm_policy_lookup_bytype(), the policy in variable
> 'ret' shows refcnt=0 under problem situation.
> > This creates an infinite loop in  xfrm_policy_lookup_bytype() and hence the
> lockup.
> >
> > Can some body please provide me pointers about 'refcnt'?
> > Is it legitimate for 'refcnt' to become '0'? Under what condition can it
> become '0'?
> 
> Yes, when policy is destroyed and the last user calls
> xfrm_pol_put() which will invoke call_rcu to free the structure.

It seems that policy reference count never gets decremented during packet ipsec encap.
It is getting incremented for every frame that hits the policy.
In setkey -DP output, I see refcnt to be wrapping around after '0'.

Is this designed to be like this or is it weird?