Re: [cocci] patch idea: convert trivial call_rcu users to kfree_rcu

[Uladzislau Rezki <urezki@gmail.com>]

> > 
> > These look ok to me.  In the last two cases, the callback function is also
> > stored in a data structure, eg:
> > 
> > static struct mfc6_cache *ip6mr_cache_alloc(void)
> > {
> > 	struct mfc6_cache *c = kmem_cache_zalloc(mrt_cachep, GFP_KERNEL);
> > 	if (!c)
> > 		return NULL;
> > 	c->_c.mfc_un.res.last_assert = jiffies - MFC_ASSERT_THRESH - 1;
> > 	c->_c.mfc_un.res.minvif = MAXMIFS;
> > 	c->_c.free = ip6mr_cache_free_rcu;
> > 	refcount_set(&c->_c.mfc_un.res.refcount, 1);
> > 	return c;
> > }
> > 
> > Should that be left as it is?
> 
> Given that ->_c.free isn't used in the RCU callback, I am guessing that
> this is intended for debugging purposes, so that you can see from a crash
> dump how this will be freed.  But I could be completely off-base here.
> 
> One approach would be to remove the ->_c.free field and call attention
> to this in the patches' commit logs.
> 
> Another would be to instead put the address of the allocation function
> in ->_c.free, and again call attention to this in the commit logs.
> 
> Is there a better approach than these three?  ;-)
> 
IMO, "_c.free" should be removed:

diff --git a/include/linux/mroute_base.h b/include/linux/mroute_base.h
index 9dd4bf157255..45f220f761df 100644
--- a/include/linux/mroute_base.h
+++ b/include/linux/mroute_base.h
@@ -130,7 +130,6 @@ enum {
  * @refcount: reference count for this entry
  * @list: global entry list
  * @rcu: used for entry destruction
- * @free: Operation used for freeing an entry under RCU
  */
 struct mr_mfc {
 	struct rhlist_head mnode;
@@ -156,13 +155,12 @@ struct mr_mfc {
 	} mfc_un;
 	struct list_head list;
 	struct rcu_head	rcu;
-	void (*free)(struct rcu_head *head);
 };
 
 static inline void mr_cache_put(struct mr_mfc *c)
 {
 	if (refcount_dec_and_test(&c->mfc_un.res.refcount))
-		call_rcu(&c->rcu, c->free);
+		kfree_rcu(c, rcu);
 }
 
 static inline void mr_cache_hold(struct mr_mfc *c)
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 6c750bd13dd8..5d2e339f09cc 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -702,16 +702,9 @@ static int vif_delete(struct mr_table *mrt, int vifi, int notify,
 	return 0;
 }
 
-static void ipmr_cache_free_rcu(struct rcu_head *head)
-{
-	struct mr_mfc *c = container_of(head, struct mr_mfc, rcu);
-
-	kmem_cache_free(mrt_cachep, (struct mfc_cache *)c);
-}
-
 static void ipmr_cache_free(struct mfc_cache *c)
 {
-	call_rcu(&c->_c.rcu, ipmr_cache_free_rcu);
+	kfree_rcu(c, _c.rcu);
 }
 
 /* Destroy an unresolved cache entry, killing queued skbs
@@ -959,7 +952,6 @@ static struct mfc_cache *ipmr_cache_alloc(void)
 	if (c) {
 		c->_c.mfc_un.res.last_assert = jiffies - MFC_ASSERT_THRESH - 1;
 		c->_c.mfc_un.res.minvif = MAXVIFS;
-		c->_c.free = ipmr_cache_free_rcu;
 		refcount_set(&c->_c.mfc_un.res.refcount, 1);
 	}
 	return c;
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index dd342e6ecf3f..1634fa794ea2 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -753,16 +753,9 @@ static int mif6_delete(struct mr_table *mrt, int vifi, int notify,
 	return 0;
 }
 
-static inline void ip6mr_cache_free_rcu(struct rcu_head *head)
-{
-	struct mr_mfc *c = container_of(head, struct mr_mfc, rcu);
-
-	kmem_cache_free(mrt_cachep, (struct mfc6_cache *)c);
-}
-
 static inline void ip6mr_cache_free(struct mfc6_cache *c)
 {
-	call_rcu(&c->_c.rcu, ip6mr_cache_free_rcu);
+	kfree_rcu(c, _c.rcu);
 }
 
 /* Destroy an unresolved cache entry, killing queued skbs
@@ -985,7 +978,6 @@ static struct mfc6_cache *ip6mr_cache_alloc(void)
 		return NULL;
 	c->_c.mfc_un.res.last_assert = jiffies - MFC_ASSERT_THRESH - 1;
 	c->_c.mfc_un.res.minvif = MAXMIFS;
-	c->_c.free = ip6mr_cache_free_rcu;
 	refcount_set(&c->_c.mfc_un.res.refcount, 1);
 	return c;
 }

--
Uladzislau Rezki