netdev - [PATCH net-next] xfrm: Use rcuref_t for xfrm

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Message-ID: <20250207210248.qy4i5Wkl@linutronix.de>
Date: Fri, 7 Feb 2025 22:02:48 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: netdev@...r.kernel.org
Cc: Steffen Klassert <steffen.klassert@...unet.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH net-next] xfrm: Use rcuref_t for xfrm_state' reference
 counting.

xfrm_state::ref is used for reference counting of xfrm_state itself. The
structure already follows RCU rules for its lifetime.

Using rcuref_t instead of refcount_t has the advantage that
refcount_inc_not_zero() can be replaced with a regular rcuref_get()
which does not suffer from a cmpxchg() loop. The cmpxchg() loop might be
repeated several times if there are puts or gets in parallel.

Replace xfrm_state's reference counting with rcuref_t. The
__xfrm_state_put() and xfrm_state_hold() which should always succeed
have a warning in case they don't succeed.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 include/net/xfrm.h    | 12 ++++++------
 net/xfrm/xfrm_state.c |  4 ++--
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index ed4b83696c77f..3da13b8a5afda 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>
@@ -189,7 +189,7 @@ 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;
@@ -901,24 +901,24 @@ 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 ad2202fa82f34..ded79ec53cbdd 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -55,7 +55,7 @@ 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,
@@ -738,7 +738,7 @@ 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);
-- 
2.47.2