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

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Message-ID: <20190820093800.GN2588@breakpoint.cc>
Date:   Tue, 20 Aug 2019 11:38:00 +0200
From:   Florian Westphal <fw@...len.de>
To:     Vakul Garg <vakul.garg@....com>
Cc:     Florian Westphal <fw@...len.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Help needed - Kernel lockup while running ipsec

Vakul Garg <vakul.garg@....com> wrote:
> 
> 
> > -----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.

Normally policy reference counts get decremented when the skb is free'd, via dst
destruction (xfrm_dst_destroy()).

Do you see a dst leak as well?