Hello,
On Sun, 10 Mar 2013, David Miller wrote:
> From: Julian Anastasov <ja@xxxxxx>
> Date: Sat, 9 Mar 2013 23:16:41 +0200
>
> > skb_dst_set_unref will use noref version even for
> > DST_NOCACHE entries because DST_NOCACHE means dst is not
> > cached in routing structures, still dst could be cached
> > by routing users and used to produce noref instances.
> >
> > Signed-off-by: Julian Anastasov <ja@xxxxxx>
>
> I'm fine with this approach, but I think the name of this
> interface could be better.
>
> In fact you could do something like:
>
> 1) Rename skb_dst_set_noref() to __skb_dst_set_noref() and add
> a new "bool force" parameter. DST_NOCACHE check is overriden
> when 'force' is true.
>
> 2) skb_dst_set_noref() is an inline that passes 'force' as false.
>
> 3) New interface skb_dst_set_noref_force() passes 'force' as true
> and will be used by your IPVS changes.
>
> Then all of the RCU checks etc. happen in one shared function.
The idea looks good, here is the implementation.
Can I use it in this form for next patchset versions?
net: add skb_dst_set_noref_force
Rename skb_dst_set_noref to __skb_dst_set_noref and
add force flag as suggested by David Miller. The new wrapper
skb_dst_set_noref_force will force dst entries that are not
cached to be attached as skb dst without taking reference
as long as provided dst is reclaimed after RCU grace period.
Signed-off-by: Julian Anastasov <ja@xxxxxx>
---
include/linux/skbuff.h | 35 ++++++++++++++++++++++++++++++++++-
net/core/dst.c | 7 ++++---
2 files changed, 38 insertions(+), 4 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 821c7f4..e8ae1d6 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -570,7 +570,40 @@ static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
skb->_skb_refdst = (unsigned long)dst;
}
-extern void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst);
+extern void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst,
+ bool force);
+
+/**
+ * skb_dst_set_noref - sets skb dst, hopefully, without taking reference
+ * @skb: buffer
+ * @dst: dst entry
+ *
+ * Sets skb dst, assuming a reference was not taken on dst.
+ * If dst entry is cached, we do not take reference and dst_release
+ * will be avoided by refdst_drop. If dst entry is not cached, we take
+ * reference, so that last dst_release can destroy the dst immediately.
+ */
+static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
+{
+ __skb_dst_set_noref(skb, dst, false);
+}
+
+/**
+ * skb_dst_set_noref_force - sets skb dst, without taking reference
+ * @skb: buffer
+ * @dst: dst entry
+ *
+ * Sets skb dst, assuming a reference was not taken on dst.
+ * No reference is taken and no dst_release will be called. While for
+ * cached dsts deferred reclaim is a basic feature, for entries that are
+ * not cached it is caller's job to guarantee that last dst_release for
+ * provided dst happens when nobody uses it, eg. after a RCU grace period.
+ */
+static inline void skb_dst_set_noref_force(struct sk_buff *skb,
+ struct dst_entry *dst)
+{
+ __skb_dst_set_noref(skb, dst, true);
+}
/**
* skb_dst_is_noref - Test if skb dst isn't refcounted
diff --git a/net/core/dst.c b/net/core/dst.c
index 35fd12f..488d53c 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -320,20 +320,21 @@ void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
EXPORT_SYMBOL(__dst_destroy_metrics_generic);
/**
- * skb_dst_set_noref - sets skb dst, without a reference
+ * __skb_dst_set_noref - sets skb dst, without a reference
* @skb: buffer
* @dst: dst entry
+ * @force: if force is set, use noref version even for DST_NOCACHE entries
*
* Sets skb dst, assuming a reference was not taken on dst
* skb_dst_drop() should not dst_release() this dst
*/
-void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
+void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst, bool force)
{
WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
/* If dst not in cache, we must take a reference, because
* dst_release() will destroy dst as soon as its refcount becomes zero
*/
- if (unlikely(dst->flags & DST_NOCACHE)) {
+ if (unlikely(dst->flags & DST_NOCACHE && !force)) {
dst_hold(dst);
skb_dst_set(skb, dst);
} else {
--
1.7.3.4
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