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Message-ID: <1524846247.11756.60.camel@redhat.com>
Date: Fri, 27 Apr 2018 12:24:07 -0400
From: Doug Ledford <dledford@...hat.com>
To: Yanjun Zhu <yanjun.zhu@...cle.com>, monis@...lanox.com,
jgg@...pe.ca, linux-rdma@...r.kernel.org
Cc: netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] IB/rxe: avoid double kfree_skb
On Wed, 2018-04-25 at 14:56 +0800, Yanjun Zhu wrote:
> Hi, all
>
> rxe_send [rdma_rxe]
> ip_local_out
> __ip_local_out
> ip_output
> ip_finish_output
> ip_finish_output2
> dev_queue_xmit
> __dev_queue_xmit
> dev_hard_start_xmit
> e1000_xmit_frame [e1000]
>
> When skb is sent, it will pass the above functions. I checked all the
> above functions. If error occurs in the above functions after
> ip_local_out, kfree_skb will be called.
> So when ip_local_out returns an error, skb should be freed. It is not
> necessary to call kfree_skb in soft roce module again.
>
> If I am wrong, please correct me.
No one from netdev has spoken up, and I don't see where you are wrong,
so I've applied this to for-rc. Thanks.
> Zhu Yanjun
> On 2018/4/24 16:34, Yanjun Zhu wrote:
> > Hi, all
> >
> > rxe_send
> > ip_local_out
> > __ip_local_out
> > nf_hook_slow
> >
> > In the above call process, nf_hook_slow drops and frees skb, then
> > -EPERM is returned when iptables rules(iptables -I OUTPUT -p udp
> > --dport 4791 -j DROP) is set.
> >
> > If skb->users is not changed in softroce, kfree_skb should not be
> > called in this module.
> >
> > I will make further investigations about other error handler after
> > ip_local_out.
> > If I am wrong, please correct me.
> >
> > Any reply is appreciated.
> >
> > Zhu Yanjun
> > On 2018/4/20 13:46, Yanjun Zhu wrote:
> > >
> > >
> > > On 2018/4/20 10:19, Doug Ledford wrote:
> > > > On Thu, 2018-04-19 at 10:01 -0400, Zhu Yanjun wrote:
> > > > > When skb is dropped by iptables rules, the skb is freed at the same
> > > > > time
> > > > > -EPERM is returned. So in softroce, it is not necessary to free skb
> > > > > again.
> > > > > Or else, crash will occur.
> > > > >
> > > > > The steps to reproduce:
> > > > >
> > > > > server client
> > > > > --------- ---------
> > > > > |1.1.1.1|<----rxe-channel--->|1.1.1.2|
> > > > > --------- ---------
> > > > >
> > > > > On server: rping -s -a 1.1.1.1 -v -C 10000 -S 512
> > > > > On client: rping -c -a 1.1.1.1 -v -C 10000 -S 512
> > > > >
> > > > > The kernel configs CONFIG_DEBUG_KMEMLEAK and
> > > > > CONFIG_DEBUG_OBJECTS are enabled on both server and client.
> > > > >
> > > > > When rping runs, run the following command in server:
> > > > >
> > > > > iptables -I OUTPUT -p udp --dport 4791 -j DROP
> > > > >
> > > > > Without this patch, crash will occur.
> > > > >
> > > > > CC: Srinivas Eeda <srinivas.eeda@...cle.com>
> > > > > CC: Junxiao Bi <junxiao.bi@...cle.com>
> > > > > Signed-off-by: Zhu Yanjun <yanjun.zhu@...cle.com>
> > > > > Reviewed-by: Yuval Shaia <yuval.shaia@...cle.com>
> > > >
> > > > I have no reason to doubt your analysis, but if there are a bunch of
> > > > error paths for net_xmit and they all return with your skb still being
> > > > valid and holding a reference, and then one oddball that returns with
> > > > your skb already gone, that just sounds like a mistake waiting to
> > > > happen
> > > > (not to mention a bajillion special cases sprinkled everywhere to deal
> > > > with this apparent inconsistency).
> > > >
> > > > Can we get a netdev@ confirmation on this being the right solution?
> > >
> > > Yes. I agree with you.
> > > After iptables rule "iptables -I OUTPUT -p udp --dport 4791 -j
> > > DROP", the skb is freed in this function
> > >
> > > /* Returns 1 if okfn() needs to be executed by the caller,
> > > * -EPERM for NF_DROP, 0 otherwise. Caller must hold rcu_read_lock. */
> > > int nf_hook_slow(struct sk_buff *skb, struct nf_hook_state *state,
> > > const struct nf_hook_entries *e, unsigned int s)
> > > {
> > > unsigned int verdict;
> > > int ret;
> > >
> > > for (; s < e->num_hook_entries; s++) {
> > > verdict = nf_hook_entry_hookfn(&e->hooks[s], skb,
> > > state);
> > > switch (verdict & NF_VERDICT_MASK) {
> > > case NF_ACCEPT:
> > > break;
> > > case NF_DROP:
> > > kfree_skb(skb); <----here, skb is freed
> > > ret = NF_DROP_GETERR(verdict);
> > > if (ret == 0)
> > > ret = -EPERM;
> > > return ret;
> > > case NF_QUEUE:
> > > ret = nf_queue(skb, state, e, s, verdict);
> > > if (ret == 1)
> > > continue;
> > > return ret;
> > > default:
> > > /* Implicit handling for NF_STOLEN, as well
> > > as any other
> > > * non conventional verdicts.
> > > */
> > > return 0;
> > > }
> > > }
> > >
> > > return 1;
> > > }
> > > EXPORT_SYMBOL(nf_hook_slow);
> > >
> > > If I am wrong, please correct me.
> > >
> > > And my test environment is still there, any solution can be verified
> > > in it.
> > >
> > > Zhu Yanjun
> > > >
> > > > > ---
> > > > > drivers/infiniband/sw/rxe/rxe_net.c | 3 +++
> > > > > drivers/infiniband/sw/rxe/rxe_req.c | 5 +++--
> > > > > drivers/infiniband/sw/rxe/rxe_resp.c | 9 ++++++---
> > > > > 3 files changed, 12 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/drivers/infiniband/sw/rxe/rxe_net.c
> > > > > b/drivers/infiniband/sw/rxe/rxe_net.c
> > > > > index 9da6e37..2094434 100644
> > > > > --- a/drivers/infiniband/sw/rxe/rxe_net.c
> > > > > +++ b/drivers/infiniband/sw/rxe/rxe_net.c
> > > > > @@ -511,6 +511,9 @@ int rxe_send(struct rxe_pkt_info *pkt, struct
> > > > > sk_buff *skb)
> > > > > if (unlikely(net_xmit_eval(err))) {
> > > > > pr_debug("error sending packet: %d\n", err);
> > > > > + /* -EPERM means the skb is dropped and freed. */
> > > > > + if (err == -EPERM)
> > > > > + return -EPERM;
> > > > > return -EAGAIN;
> > > > > }
> > > > > diff --git a/drivers/infiniband/sw/rxe/rxe_req.c
> > > > > b/drivers/infiniband/sw/rxe/rxe_req.c
> > > > > index 7bdaf71..9d2efec 100644
> > > > > --- a/drivers/infiniband/sw/rxe/rxe_req.c
> > > > > +++ b/drivers/infiniband/sw/rxe/rxe_req.c
> > > > > @@ -727,8 +727,9 @@ int rxe_requester(void *arg)
> > > > > rollback_state(wqe, qp, &rollback_wqe,
> > > > > rollback_psn);
> > > > > - if (ret == -EAGAIN) {
> > > > > - kfree_skb(skb);
> > > > > + if ((ret == -EAGAIN) || (ret == -EPERM)) {
> > > > > + if (ret == -EAGAIN)
> > > > > + kfree_skb(skb);
> > > > > rxe_run_task(&qp->req.task, 1);
> > > > > goto exit;
> > > > > }
> > > > > diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c
> > > > > b/drivers/infiniband/sw/rxe/rxe_resp.c
> > > > > index a65c996..6bdf9b2 100644
> > > > > --- a/drivers/infiniband/sw/rxe/rxe_resp.c
> > > > > +++ b/drivers/infiniband/sw/rxe/rxe_resp.c
> > > > > @@ -742,7 +742,8 @@ static enum resp_states read_reply(struct
> > > > > rxe_qp *qp,
> > > > > err = rxe_xmit_packet(rxe, qp, &ack_pkt, skb);
> > > > > if (err) {
> > > > > pr_err("Failed sending RDMA reply.\n");
> > > > > - kfree_skb(skb);
> > > > > + if (err != -EPERM)
> > > > > + kfree_skb(skb);
> > > > > return RESPST_ERR_RNR;
> > > > > }
> > > > > @@ -956,7 +957,8 @@ static int send_ack(struct rxe_qp *qp, struct
> > > > > rxe_pkt_info *pkt,
> > > > > err = rxe_xmit_packet(rxe, qp, &ack_pkt, skb);
> > > > > if (err) {
> > > > > pr_err_ratelimited("Failed sending ack\n");
> > > > > - kfree_skb(skb);
> > > > > + if (err != -EPERM)
> > > > > + kfree_skb(skb);
> > > > > }
> > > > > err1:
> > > > > @@ -1141,7 +1143,8 @@ static enum resp_states
> > > > > duplicate_request(struct rxe_qp *qp,
> > > > > if (rc) {
> > > > > pr_err("Failed resending result.
> > > > > This flow is not handled - skb ignored\n");
> > > > > rxe_drop_ref(qp);
> > > > > - kfree_skb(skb_copy);
> > > > > + if (rc != -EPERM)
> > > > > + kfree_skb(skb_copy);
> > > > > rc = RESPST_CLEANUP;
> > > > > goto out;
> > > > > }
> > > > > --
> > > > > 2.7.4
> > > > >
> > >
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
> > > the body of a message to majordomo@...r.kernel.org
> > > More majordomo info at http://vger.kernel.org/majordomo-info.html
>
>
--
Doug Ledford <dledford@...hat.com>
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