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

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Date:   Mon, 19 Aug 2019 19:38:10 +0200
From:   Florian Westphal <fw@...len.de>
To:     Vakul Garg <vakul.garg@....com>
Cc:     "netdev@...r.kernel.org" <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.