Subject: Re: [PATCH ipsec] net: xfrm_policy: fix device unregistration hang

From: Eyal Birger <[email-masked]>
Date: Mon, 12 Feb 2018 20:34:38 +0200

On Mon, 12 Feb 2018 09:55:48 -0800
Shannon Nelson <[email-masked]> wrote:

> On 2/12/2018 9:21 AM, Eyal Birger wrote:
> > In setups like the following:
> > 
> >         Host A          --        Host B
> > tun0 -- ipsec -- eth0  --  eth0 -- ipsec -- tun0
> > 
> > where tun0 are tunnel devices using dst_cache (ipip, ipip6, etc...).
> > 
> > Unregistration of an underlying eth0 device leads to the following
> > log messages:
> > 
> > unregister_netdevice: waiting for eth0 to become free. Usage count
> > = 2
> > 
> > This is since xfrm dsts device references are not released upon
> > device unregistration when the xfrm dst is cached in a dst_cache.
> > 
> > Several approaches for fixing this were discussed in [1]; this
> > commit keeps track of allocated xdsts and releases their device
> > references on a netdev unregister event.
> > 
> > Signed-off-by: Eyal Birger <[email-masked]>
> > 
> > [1] https://patchwork.ozlabs.org/patch/869025/
> > ---
> >   include/net/xfrm.h     | 10 ++-----
> >   net/xfrm/xfrm_policy.c | 81
> > ++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed,
> > 84 insertions(+), 7 deletions(-)
> > 
> > diff --git a/include/net/xfrm.h b/include/net/xfrm.h
> > index 7d20776..c1c8493 100644
> > --- a/include/net/xfrm.h
> > +++ b/include/net/xfrm.h
> > @@ -994,6 +994,8 @@ struct xfrm_dst {
> >   	u32 child_mtu_cached;
> >   	u32 route_cookie;
> >   	u32 path_cookie;
> > +	struct list_head xfrm_dst_gc;
> > +	struct xfrm_dst_list *xfrm_dst_gc_list;
> >   };
> >   
> >   static inline struct dst_entry *xfrm_dst_path(const struct
> > dst_entry *dst) @@ -1025,13 +1027,7 @@ static inline void
> > xfrm_dst_set_child(struct xfrm_dst *xdst, struct dst_entry *c
> > xdst->child = child; }
> >   
> > -static inline void xfrm_dst_destroy(struct xfrm_dst *xdst)
> > -{
> > -	xfrm_pols_put(xdst->pols, xdst->num_pols);
> > -	dst_release(xdst->route);
> > -	if (likely(xdst->u.dst.xfrm))
> > -		xfrm_state_put(xdst->u.dst.xfrm);
> > -}
> > +void xfrm_dst_destroy(struct xfrm_dst *xdst);
> >   #endif
> >   
> >   void xfrm_dst_ifdown(struct dst_entry *dst, struct net_device
> > *dev); diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> > index 7a23078..1da8a65 100644
> > --- a/net/xfrm/xfrm_policy.c
> > +++ b/net/xfrm/xfrm_policy.c
> > @@ -45,6 +45,12 @@ struct xfrm_flo {
> >   	u8 flags;
> >   };
> >   
> > +struct xfrm_dst_list {
> > +	spinlock_t lock; /* sync writers */
> > +	struct list_head head;
> > +};
> > +
> > +static DEFINE_PER_CPU_ALIGNED(struct xfrm_dst_list,
> > xfrm_dst_gc_list); static DEFINE_PER_CPU(struct xfrm_dst *,
> > xfrm_last_dst); static struct work_struct *xfrm_pcpu_work
> > __read_mostly; static DEFINE_SPINLOCK(xfrm_policy_afinfo_lock);
> > @@ -94,6 +100,51 @@ __xfrm6_selector_match(const struct
> > xfrm_selector *sel, const struct flowi *fl) (fl6->flowi6_oif ==
> > sel->ifindex || !sel->ifindex); }
> >   
> > +static void xfrm_dst_add_to_gc_list(struct xfrm_dst *xdst)
> > +{
> > +	struct xfrm_dst_list *xl = raw_cpu_ptr(&xfrm_dst_gc_list);
> > +
> > +	xdst->xfrm_dst_gc_list = xl;
> > +
> > +	spin_lock_bh(&xl->lock);
> > +	list_add_tail(&xdst->xfrm_dst_gc, &xl->head);
> > +	spin_unlock_bh(&xl->lock);
> > +}
> > +
> > +void xfrm_dst_destroy(struct xfrm_dst *xdst)
> > +{
> > +	xfrm_pols_put(xdst->pols, xdst->num_pols);
> > +	dst_release(xdst->route);
> > +	if (likely(xdst->u.dst.xfrm))
> > +		xfrm_state_put(xdst->u.dst.xfrm);
> > +	if (!list_empty(&xdst->xfrm_dst_gc)) {
> > +		struct xfrm_dst_list *xl = xdst->xfrm_dst_gc_list;
> > +
> > +		spin_lock_bh(&xl->lock);
> > +		list_del(&xdst->xfrm_dst_gc);
> > +		spin_unlock_bh(&xl->lock);
> > +	}
> > +}
> > +EXPORT_SYMBOL_GPL(xfrm_dst_destroy);
> > +
> > +static void xfrm_flush_dev(struct net_device *dev)
> > +{
> > +	struct xfrm_dst *xdst;
> > +	int cpu;
> > +
> > +	for_each_possible_cpu(cpu) {
> > +		struct xfrm_dst_list *xl =
> > &per_cpu(xfrm_dst_gc_list, cpu); +
> > +		spin_lock_bh(&xl->lock);
> > +		list_for_each_entry(xdst, &xl->head, xfrm_dst_gc) {
> > +			if (xdst->u.dst.dev != dev)
> > +				continue;
> > +			dst_dev_put(&xdst->u.dst);
> > +		}
> > +		spin_unlock_bh(&xl->lock);
> > +	}
> > +}
> > +
> >   bool xfrm_selector_match(const struct xfrm_selector *sel, const
> > struct flowi *fl, unsigned short family)
> >   {
> > @@ -1581,6 +1632,8 @@ static struct dst_entry
> > *xfrm_bundle_create(struct xfrm_policy *policy, }
> >   
> >   		bundle[i] = xdst;
> > +		xfrm_dst_add_to_gc_list(xdst);
> > +
> >   		if (!xdst_prev)
> >   			xdst0 = xdst;
> >   		else
> > @@ -2937,6 +2990,20 @@ static void xfrm_policy_fini(struct net *net)
> >   	xfrm_hash_free(net->xfrm.policy_byidx, sz);
> >   }
> >   
> > +static int xfrm_netdev_event(struct notifier_block *this, unsigned
> > long event,
> > +			     void *ptr)
> > +{
> > +	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
> > +
> > +	if (event == NETDEV_UNREGISTER)
> > +		xfrm_flush_dev(dev);
> > +	return NOTIFY_DONE;
> > +}
> > +
> > +static struct notifier_block xfrm_netdev_notifier = {
> > +	.notifier_call = xfrm_netdev_event,
> > +};
> > +  
> 
> Instead of creating yet another netdev notifier, can this be wired
> into xfrm_dev_unregister(), the existing notifier in xfrm_decide.c
> which calls into xfrm_policy_cache_flush()?

I don't mind doing so... I was under the impression that xfrm_device.c
is designated to device offload (as indicated by the top level comment) -
though as you mentioned, xfrm_policy_cache_flush() is indeed called from
there.

Thanks!
Eyal.