Messages in this thread | | | Date | Tue, 31 May 2011 12:11:15 -0400 | From | Neil Horman <> | Subject | Re: [PATCH] ftrace: tracepoint of net_dev_xmit sees freed skb and causes panic |
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On Tue, May 31, 2011 at 11:13:11AM -0400, Steven Rostedt wrote: > On Tue, 2011-05-31 at 16:48 +0900, Koki Sanagi wrote: > > Because there is a possibility that skb is kfree_skb()ed and zero cleared > > after ndo_start_xmit, we should not see the contents of skb like skb->len and > > skb->dev->name after ndo_start_xmit. But trace_net_dev_xmit does that > > and causes panic by NULL pointer dereference. > > This patch fixes trace_net_dev_xmit not to see the contents of skb directly. > > > > > > if (likely(!skb->next)) { > > u32 features; > > @@ -2139,8 +2140,9 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev, > > } > > } > > > > + skb_len = skb->len; > > rc = ops->ndo_start_xmit(skb, dev); > > - trace_net_dev_xmit(skb, rc); > > + trace_net_dev_xmit(skb, rc, dev, skb_len); > > if (rc == NETDEV_TX_OK) > > txq_trans_update(txq); > > return rc; > > @@ -2160,8 +2162,9 @@ gso: > > if (dev->priv_flags & IFF_XMIT_DST_RELEASE) > > skb_dst_drop(nskb); > > > > + skb_len = nskb->len; > > rc = ops->ndo_start_xmit(nskb, dev); > > - trace_net_dev_xmit(nskb, rc); > > + trace_net_dev_xmit(nskb, rc, dev, skb_len); > > What if you just put the tracepoint before the call to > ops->ndo_start_xmit? > Then you won't know the return code of ndo_start_xmit, which this tracepoint records. Neil
> -- Steve > > > if (unlikely(rc != NETDEV_TX_OK)) { > > if (rc & ~NETDEV_TX_MASK) > > goto out_kfree_gso_skb; > > >
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