On Thu, 2017-09-21 at 11:06 +0200, Paweł Staszewski wrote:
>
> W dniu 2017-09-21 o 03:17, Eric Dumazet pisze:
> > On Wed, 2017-09-20 at 18:09 -0700, Wei Wang wrote:
> >>> Thanks very much Pawel for the feedback.
> >>>
> >>> I was looking into the code (specifically IPv4 part) and found that in
> >>> free_fib_info_rcu(), we call free_nh_exceptions() without holding the
> >>> fnhe_lock. I am wondering if that could cause some race condition on
> >>> fnhe->fnhe_rth_input/output so a double call on dst_dev_put() on the
> >>> same dst could be happening.
> >>>
> >>> But as we call free_fib_info_rcu() only after the grace period, and
> >>> the lookup code which could potentially modify
> >>> fnhe->fnhe_rth_input/output all holds rcu_read_lock(), it seems
> >>> fine...
> >>>
> >> Hi Pawel,
> >>
> >> Could you try the following debug patch on top of net-next branch and
> >> reproduce the issue check if there are warning msg showing?
> >>
> >> diff --git a/include/net/dst.h b/include/net/dst.h
> >> index 93568bd0a352..82aff41c6f63 100644
> >> --- a/include/net/dst.h
> >> +++ b/include/net/dst.h
> >> @@ -271,7 +271,7 @@ static inline void dst_use_noref(struct dst_entry
> >> *dst, unsigned long time)
> >> static inline struct dst_entry *dst_clone(struct dst_entry *dst)
> >> {
> >> if (dst)
> >> - atomic_inc(&dst->__refcnt);
> >> + dst_hold(dst);
> >> return dst;
> >> }
> >>
> >> Thanks.
> >> Wei
> >>
> >
> > Yes, we believe skb_dst_force() and skb_dst_force_safe() should be
> > unified (to the 'safe' version)
> >
> > We no longer have gc to protect from 0 -> 1 transition of dst refcount.
> >
> >
> >
> >
>
> After adding patch from Wei
> https://bugzilla.kernel.org/show_bug.cgi?id=197005#c14
>
OK we have two problems here
1) We need to unify skb_dst_force() ( for net tree )
2) Vlan devices should try to correctly handle IFF_XMIT_DST_RELEASE from
lower device. This will considerably help your performance.
For 1), this is what I had in mind, can you try it ?
Thanks a lot !
diff --git a/include/net/dst.h b/include/net/dst.h
index
93568bd0a3520bb7402f04d90cf04ac99c81cfbe..f23851eeaad917e8dafc06b58d23a2575405c894
100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -271,7 +271,7 @@ static inline void dst_use_noref(struct dst_entry *dst,
unsigned long time)
static inline struct dst_entry *dst_clone(struct dst_entry *dst)
{
if (dst)
- atomic_inc(&dst->__refcnt);
+ dst_hold(dst);
return dst;
}
@@ -311,21 +311,6 @@ static inline void skb_dst_copy(struct sk_buff *nskb,
const struct sk_buff *oskb
__skb_dst_copy(nskb, oskb->_skb_refdst);
}
-/**
- * skb_dst_force - makes sure skb dst is refcounted
- * @skb: buffer
- *
- * If dst is not yet refcounted, let's do it
- */
-static inline void skb_dst_force(struct sk_buff *skb)
-{
- if (skb_dst_is_noref(skb)) {
- WARN_ON(!rcu_read_lock_held());
- skb->_skb_refdst &= ~SKB_DST_NOREF;
- dst_clone(skb_dst(skb));
- }
-}
-
/**
* dst_hold_safe - Take a reference on a dst if possible
* @dst: pointer to dst entry
@@ -356,6 +341,23 @@ static inline void skb_dst_force_safe(struct sk_buff *skb)
}
}
+/**
+ * skb_dst_force - makes sure skb dst is refcounted
+ * @skb: buffer
+ *
+ * If dst is not yet refcounted, let's do it
+ */
+static inline void skb_dst_force(struct sk_buff *skb)
+{
+ if (skb_dst_is_noref(skb)) {
+ struct dst_entry *dst = skb_dst(skb);
+
+ WARN_ON(!rcu_read_lock_held());
+ if (!dst_hold_safe(dst))
+ dst = NULL;
+ skb->_skb_refdst = (unsigned long)dst;
+ }
+}
/**
* __skb_tunnel_rx - prepare skb for rx reinsert
