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Date: Wed, 21 Aug 2019 07:37:25 +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: Vakul Garg > Sent: Tuesday, August 20, 2019 4:08 PM > To: Florian Westphal <fw@...len.de> > Cc: 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 3:08 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: > > > > > > > > > > > > > -----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? > > > > Can you please guide me how to detect it? > > > > (I am checking refcount on recent kernel and will let you know.) > > Policy refcount is decreasing properly on 4.19. > Same should be on the latest kernel too. On kernel-4.14, I find dst_release() is getting called through xfrm_output_one(). However since dst->__refcnt gets decremented to '1', the call_rcu(&dst->rcu_head, dst_destroy_rcu) is not invoked. On kernel-4.19, dst->__refcnt gets decremented to '0', hence things fall in place and dst_destroy_rcu() eventually executes. Any further help/pointers for kernel-4.14 would be deeply appreciated.
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