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

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Message-ID: <DB7PR04MB4620487074796FBC015AFD098BAB0@DB7PR04MB4620.eurprd04.prod.outlook.com>
Date:   Tue, 20 Aug 2019 09:26:06 +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



> -----Original Message-----
> From: Florian Westphal <fw@...len.de>
> Sent: Tuesday, August 20, 2019 2:53 PM
> To: Vakul Garg <vakul.garg@....com>
> Cc: Florian Westphal <fw@...len.de>; netdev@...r.kernel.org
> Subject: Re: Help needed - Kernel lockup while running ipsec
> 
> Vakul Garg <vakul.garg@....com> wrote:
> > > > 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'.
> 
> Thats a bug.  Does this affect 4.14 only or does this happen on current tree
> as well?
 
I am yet to try it on 4.19.
Can you help me with the right fix? Which part of code should it get decremented?
I am not conversant with xfrm code.