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

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

[David Windsor]

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 Juilan 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>
---
 include/net/ip_vs.h            | 2 +-
 net/netfilter/ipvs/ip_vs_ctl.c | 4 +---
 2 files changed, 2 insertions(+), 4 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..6b5492e 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;
 		}
 	}
@@ -1084,7 +1083,6 @@ static void __ip_vs_del_dest(struct netns_ipvs *ipvs, struct ip_vs_dest *dest,
 	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

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

[Julian Anastasov]

	Hello,

On Tue, 24 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 Juilan Anastasov: "The problem is that dest_trash currently holds deleted

	Julian

> 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().

	Too long lines, should be up to 75 columns as per
Documentation/process/submitting-patches.rst

	Check with: scripts/checkpatch.pl --strict /tmp/file.patch

> Signed-off-by: David Windsor <dwindsor@gmail.com>
> ---
>  include/net/ip_vs.h            | 2 +-
>  net/netfilter/ipvs/ip_vs_ctl.c | 4 +---
>  2 files changed, 2 insertions(+), 4 deletions(-)
> 

> diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
> index 55e0169..6b5492e 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;
>  		}
>  	}

	The changes look ok to me but as this is a net-next
material I also prefer some comments in the code to be updated:

- "be 0, so we simply release them here" before ip_vs_trash_cleanup
should become "be 1, so we simply release them here".

- "dest lives in trash with[out] reference" in __ip_vs_del_dest

	When sending v2 for net-next please also CC:

Simon Horman <horms@verge.net.au>
Pablo Neira Ayuso <pablo@netfilter.org>
lvs-devel@vger.kernel.org

	I'll ack the next version after some tests...

Regards

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

[David Miller]

From: Julian Anastasov <ja@ssi.bg>
Date: Tue, 24 Jan 2017 23:14:29 +0200 (EET)

> 	The changes look ok to me but as this is a net-next
> material I also prefer some comments in the code to be updated:

It also needs to be posted to netfilter-devel with the IPVS maintainer
CC:'d