Re: [PATCH v2 net] net: free ip_vs_dest structs when refcnt=0

[Simon Horman <horms@verge.net.au>]

On Thu, Jan 26, 2017 at 10:49:10PM +0200, Julian Anastasov wrote:
> 
> 	Hello,
> 
> On Mon, 23 Jan 2017, David Windsor wrote:
> 
> > Currently, the ip_vs_dest cache frees ip_vs_dest objects when their
> > reference count becomes < 0.  Aside from not being semantically sound,
> > this is problematic for the new type refcount_t, which will be introduced
> > shortly in a separate patch. refcount_t is the new kernel type for
> > holding reference counts, and provides overflow protection and a
> > constrained interface relative to atomic_t (the type currently being
> > used for kernel reference counts).
> > 
> > Per Julian Anastasov: "The problem is that dest_trash currently holds
> > deleted dests (unlinked from RCU lists) with refcnt=0."  Changing
> > dest_trash to hold dest with refcnt=1 will allow us to free ip_vs_dest
> > structs when their refcnt=0, in ip_vs_dest_put_and_free().
> > 
> > Signed-off-by: David Windsor <dwindsor@gmail.com>
> 
> 	Thanks! I tested the first version and this one
> just adds the needed changes in comments, so
> 
> Signed-off-by: Julian Anastasov <ja@ssi.bg>
> 
> 	Simon and Pablo, this is more appropriate for
> ipvs-next/nf-next. Please apply!

Pablo, would you mind taking this one directly into nf-next?

Signed-off-by: Simon Horman <horms@verge.net.au>

> 
> > ---
> >  include/net/ip_vs.h            | 2 +-
> >  net/netfilter/ipvs/ip_vs_ctl.c | 8 +++-----
> >  2 files changed, 4 insertions(+), 6 deletions(-)
> > 
> > diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
> > index cd6018a..a3e78ad 100644
> > --- a/include/net/ip_vs.h
> > +++ b/include/net/ip_vs.h
> > @@ -1421,7 +1421,7 @@ static inline void ip_vs_dest_put(struct ip_vs_dest *dest)
> >  
> >  static inline void ip_vs_dest_put_and_free(struct ip_vs_dest *dest)
> >  {
> > -	if (atomic_dec_return(&dest->refcnt) < 0)
> > +	if (atomic_dec_and_test(&dest->refcnt))
> >  		kfree(dest);
> >  }
> >  
> > diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
> > index 55e0169..5fc4836 100644
> > --- a/net/netfilter/ipvs/ip_vs_ctl.c
> > +++ b/net/netfilter/ipvs/ip_vs_ctl.c
> > @@ -711,7 +711,6 @@ ip_vs_trash_get_dest(struct ip_vs_service *svc, int dest_af,
> >  		      dest->vport == svc->port))) {
> >  			/* HIT */
> >  			list_del(&dest->t_list);
> > -			ip_vs_dest_hold(dest);
> >  			goto out;
> >  		}
> >  	}
> > @@ -741,7 +740,7 @@ static void ip_vs_dest_free(struct ip_vs_dest *dest)
> >   *  When the ip_vs_control_clearup is activated by ipvs module exit,
> >   *  the service tables must have been flushed and all the connections
> >   *  are expired, and the refcnt of each destination in the trash must
> > - *  be 0, so we simply release them here.
> > + *  be 1, so we simply release them here.
> >   */
> >  static void ip_vs_trash_cleanup(struct netns_ipvs *ipvs)
> >  {
> > @@ -1080,11 +1079,10 @@ static void __ip_vs_del_dest(struct netns_ipvs *ipvs, struct ip_vs_dest *dest,
> >  	if (list_empty(&ipvs->dest_trash) && !cleanup)
> >  		mod_timer(&ipvs->dest_trash_timer,
> >  			  jiffies + (IP_VS_DEST_TRASH_PERIOD >> 1));
> > -	/* dest lives in trash without reference */
> > +	/* dest lives in trash with reference */
> >  	list_add(&dest->t_list, &ipvs->dest_trash);
> >  	dest->idle_start = 0;
> >  	spin_unlock_bh(&ipvs->dest_trash_lock);
> > -	ip_vs_dest_put(dest);
> >  }
> >  
> >  
> > @@ -1160,7 +1158,7 @@ static void ip_vs_dest_trash_expire(unsigned long data)
> >  
> >  	spin_lock(&ipvs->dest_trash_lock);
> >  	list_for_each_entry_safe(dest, next, &ipvs->dest_trash, t_list) {
> > -		if (atomic_read(&dest->refcnt) > 0)
> > +		if (atomic_read(&dest->refcnt) > 1)
> >  			continue;
> >  		if (dest->idle_start) {
> >  			if (time_before(now, dest->idle_start +
> > -- 
> > 2.7.4
> 
> Regards
> 
> --
> Julian Anastasov <ja@ssi.bg>
>