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dst: no need to take reference on DST_NOCACHE dsts
Since commit f886497 ("ipv4: fix dst race in sk_dst_get()") DST_NOCACHE dst_entries get freed by RCU. So there is no need to get a reference on them when we are in rcu protected sections. Cc: Eric Dumazet <edumazet@google.com> Cc: Julian Anastasov <ja@ssi.bg> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Reviewed-by: Julian Anastasov <ja@ssi.bg> Signed-off-by: David S. Miller <davem@davemloft.net>
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lines changed

3 files changed

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lines changed

include/linux/skbuff.h

Lines changed: 2 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -717,9 +717,6 @@ static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
717717
skb->_skb_refdst = (unsigned long)dst;
718718
}
719719

720-
void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst,
721-
bool force);
722-
723720
/**
724721
* skb_dst_set_noref - sets skb dst, hopefully, without taking reference
725722
* @skb: buffer
@@ -732,24 +729,8 @@ void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst,
732729
*/
733730
static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
734731
{
735-
__skb_dst_set_noref(skb, dst, false);
736-
}
737-
738-
/**
739-
* skb_dst_set_noref_force - sets skb dst, without taking reference
740-
* @skb: buffer
741-
* @dst: dst entry
742-
*
743-
* Sets skb dst, assuming a reference was not taken on dst.
744-
* No reference is taken and no dst_release will be called. While for
745-
* cached dsts deferred reclaim is a basic feature, for entries that are
746-
* not cached it is caller's job to guarantee that last dst_release for
747-
* provided dst happens when nobody uses it, eg. after a RCU grace period.
748-
*/
749-
static inline void skb_dst_set_noref_force(struct sk_buff *skb,
750-
struct dst_entry *dst)
751-
{
752-
__skb_dst_set_noref(skb, dst, true);
732+
WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
733+
skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
753734
}
754735

755736
/**

net/core/dst.c

Lines changed: 0 additions & 24 deletions
Original file line numberDiff line numberDiff line change
@@ -327,30 +327,6 @@ void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
327327
}
328328
EXPORT_SYMBOL(__dst_destroy_metrics_generic);
329329

330-
/**
331-
* __skb_dst_set_noref - sets skb dst, without a reference
332-
* @skb: buffer
333-
* @dst: dst entry
334-
* @force: if force is set, use noref version even for DST_NOCACHE entries
335-
*
336-
* Sets skb dst, assuming a reference was not taken on dst
337-
* skb_dst_drop() should not dst_release() this dst
338-
*/
339-
void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst, bool force)
340-
{
341-
WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
342-
/* If dst not in cache, we must take a reference, because
343-
* dst_release() will destroy dst as soon as its refcount becomes zero
344-
*/
345-
if (unlikely((dst->flags & DST_NOCACHE) && !force)) {
346-
dst_hold(dst);
347-
skb_dst_set(skb, dst);
348-
} else {
349-
skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
350-
}
351-
}
352-
EXPORT_SYMBOL(__skb_dst_set_noref);
353-
354330
/* Dirty hack. We did it in 2.2 (in __dst_free),
355331
* we have _very_ good reasons not to repeat
356332
* this mistake in 2.3, but we have no choice

net/netfilter/ipvs/ip_vs_xmit.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -343,7 +343,7 @@ __ip_vs_get_out_rt(int skb_af, struct sk_buff *skb, struct ip_vs_dest *dest,
343343
skb_dst_drop(skb);
344344
if (noref) {
345345
if (!local)
346-
skb_dst_set_noref_force(skb, &rt->dst);
346+
skb_dst_set_noref(skb, &rt->dst);
347347
else
348348
skb_dst_set(skb, dst_clone(&rt->dst));
349349
} else
@@ -487,7 +487,7 @@ __ip_vs_get_out_rt_v6(int skb_af, struct sk_buff *skb, struct ip_vs_dest *dest,
487487
skb_dst_drop(skb);
488488
if (noref) {
489489
if (!local)
490-
skb_dst_set_noref_force(skb, &rt->dst);
490+
skb_dst_set_noref(skb, &rt->dst);
491491
else
492492
skb_dst_set(skb, dst_clone(&rt->dst));
493493
} else

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