netdev - Re: xfrm in RT

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Message-ID: <20241218160745.G1WJ-lWR@linutronix.de>
Date: Wed, 18 Dec 2024 17:07:45 +0100
From: Sebastian Sewior <bigeasy@...utronix.de>
To: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Network Development <netdev@...r.kernel.org>,
	Jakub Kicinski <kuba@...nel.org>
Subject: Re: xfrm in RT

On 2024-12-18 16:44:27 [+0100], To Steffen Klassert wrote:
> time (your current get_cpu() -> put_cpu() span) you could do something
> like

While at, may I promote rcuref? This would get rid of your cmpxchg()
loop that you have otherwise in refcount_inc_not_zero(). In case you
have performance test:

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 32c09e85a64ce..eb152ebc0832c 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -14,7 +14,7 @@
 #include <linux/mutex.h>
 #include <linux/audit.h>
 #include <linux/slab.h>
-#include <linux/refcount.h>
+#include <linux/rcuref.h>
 #include <linux/sockptr.h>
 
 #include <net/sock.h>
@@ -188,7 +188,7 @@ struct xfrm_state {
 	struct hlist_node	state_cache;
 	struct hlist_node	state_cache_input;
 
-	refcount_t		refcnt;
+	rcuref_t		ref;
 	spinlock_t		lock;
 
 	u32			pcpu_num;
@@ -857,24 +857,24 @@ void __xfrm_state_destroy(struct xfrm_state *, bool);
 
 static inline void __xfrm_state_put(struct xfrm_state *x)
 {
-	refcount_dec(&x->refcnt);
+	WARN_ON(rcuref_put(&x->ref));
 }
 
 static inline void xfrm_state_put(struct xfrm_state *x)
 {
-	if (refcount_dec_and_test(&x->refcnt))
+	if (rcuref_put(&x->ref))
 		__xfrm_state_destroy(x, false);
 }
 
 static inline void xfrm_state_put_sync(struct xfrm_state *x)
 {
-	if (refcount_dec_and_test(&x->refcnt))
+	if (rcuref_put(&x->ref))
 		__xfrm_state_destroy(x, true);
 }
 
 static inline void xfrm_state_hold(struct xfrm_state *x)
 {
-	refcount_inc(&x->refcnt);
+	WARN_ON(!rcuref_get(&x->ref));
 }
 
 static inline bool addr_match(const void *token1, const void *token2,
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 66b108a5b87d4..35ed7c35292a3 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -53,7 +53,7 @@ static HLIST_HEAD(xfrm_state_dev_gc_list);
 
 static inline bool xfrm_state_hold_rcu(struct xfrm_state __rcu *x)
 {
-	return refcount_inc_not_zero(&x->refcnt);
+	return rcuref_get(&x->ref);
 }
 
 static inline unsigned int xfrm_dst_hash(struct net *net,
@@ -662,7 +662,7 @@ struct xfrm_state *xfrm_state_alloc(struct net *net)
 
 	if (x) {
 		write_pnet(&x->xs_net, net);
-		refcount_set(&x->refcnt, 1);
+		rcuref_init(&x->ref, 1);
 		atomic_set(&x->tunnel_users, 0);
 		INIT_LIST_HEAD(&x->km.all);
 		INIT_HLIST_NODE(&x->state_cache);

Sebastian