kcm: replace call_rcu by kfree_rcu for simple kmem_cache_free callback

Since SLOB was removed and since
commit 6c6c47b ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
it is not necessary to use call_rcu when the callback only performs
kmem_cache_free. Use kfree_rcu() directly.

The changes were made using Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://patch.msgid.link/20241013201704.49576-15-Julia.Lawall@inria.fr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/kcm/kcmsock.c

@@ -1584,14 +1584,6 @@ static int kcm_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 	return err;
 }
 
-static void free_mux(struct rcu_head *rcu)
-{
-	struct kcm_mux *mux = container_of(rcu,
-	    struct kcm_mux, rcu);
-
-	kmem_cache_free(kcm_muxp, mux);
-}
-
 static void release_mux(struct kcm_mux *mux)
 {
 	struct kcm_net *knet = mux->knet;
@@ -1619,7 +1611,7 @@ static void release_mux(struct kcm_mux *mux)
 	knet->count--;
 	mutex_unlock(&knet->mutex);
 
-	call_rcu(&mux->rcu, free_mux);
+	kfree_rcu(mux, rcu);
 }
 
 static void kcm_done(struct kcm_sock *kcm)