From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: Re: [PATCH] ftrace: tracepoint of net_dev_xmit sees freed skb and causes panic Date: Tue, 31 May 2011 11:13:11 -0400 Message-ID: <1306854791.11899.30.camel@gandalf.stny.rr.com> References: <4DE49D52.709@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-15" Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, davem@davemloft.net, nhorman@tuxdriver.com, mingo@elte.hu, fweisbec@gmail.com, mathieu.desnoyers@efficios.com, tglx@linutronix.de, kosaki.motohiro@jp.fujitsu.com, izumi.taku@jp.fujitsu.com, kaneshige.kenji@jp.fujitsu.com To: Koki Sanagi Return-path: In-Reply-To: <4DE49D52.709@jp.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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? -- Steve > if (unlikely(rc != NETDEV_TX_OK)) { > if (rc & ~NETDEV_TX_MASK) > goto out_kfree_gso_skb;