From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: [PATCH] net: orphan queued skbs if device tx can stall Date: Sun, 8 Apr 2012 20:13:25 +0300 Message-ID: <20120408171323.GA16012@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "David S. Miller" , Jamal Hadi Salim , "Michael S. Tsirkin" , Stephen Hemminger , Jason Wang , Neil Horman , Jiri Pirko , Jeff Kirsher , Eric Dumazet , =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Ben Hutchings , Herbert Xu To: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org commit 0110d6f22f392f976e84ab49da1b42f85b64a3c5 tun: orphan an skb on tx Fixed a configuration where skbs get queued at the tun device forever, blocking senders. However this fix isn't waterproof: userspace can control whether the interface is stopped, and if it is, packets get queued in the qdisc, again potentially forever. Complete the fix by setting a private flag and orphaning at the qdisc level. Signed-off-by: Michael S. Tsirkin --- drivers/net/tun.c | 3 +++ include/linux/if.h | 1 + net/core/dev.c | 5 +++++ net/sched/sch_generic.c | 5 +++++ 4 files changed, 14 insertions(+), 0 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index bb8c72c..15c5bb8 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -535,6 +535,9 @@ static void tun_net_init(struct net_device *dev) dev->tx_queue_len = TUN_READQ_SIZE; /* We prefer our own queue length */ break; } + /* Once queue becomes full, we stop tx until userspace + * dequeues some packets, that is potentially forever. */ + dev->priv_flags |= IFF_TX_CAN_STALL; } /* Character device part */ diff --git a/include/linux/if.h b/include/linux/if.h index f995c66..dd2c7f7 100644 --- a/include/linux/if.h +++ b/include/linux/if.h @@ -81,6 +81,7 @@ #define IFF_UNICAST_FLT 0x20000 /* Supports unicast filtering */ #define IFF_TEAM_PORT 0x40000 /* device used as team port */ #define IFF_SUPP_NOFCS 0x80000 /* device supports sending custom FCS */ +#define IFF_TX_CAN_STALL 0x100000 /* Device can stop tx forever */ #define IF_GET_IFACE 0x0001 /* for querying only */ diff --git a/net/core/dev.c b/net/core/dev.c index 5d59155..e812706 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -2516,6 +2516,11 @@ int dev_queue_xmit(struct sk_buff *skb) struct Qdisc *q; int rc = -ENOMEM; + /* Orphan the skb - required if we might hang on to it + * for indefinite time. */ + if (dev->priv_flags & IFF_TX_CAN_STALL) + skb_orphan(skb); + /* Disable soft irqs for various locks below. Also * stops preemption for RCU. */ diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 67fc573..27883d1 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -120,6 +120,11 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q, /* And release qdisc */ spin_unlock(root_lock); + /* Orphan the skb - required if we might hang on to it + * for indefinite time. */ + if (dev->priv_flags & IFF_TX_CAN_STALL) + skb_orphan(skb); + HARD_TX_LOCK(dev, txq, smp_processor_id()); if (!netif_xmit_frozen_or_stopped(txq)) ret = dev_hard_start_xmit(skb, dev, txq); -- 1.7.9.111.gf3fb0