From 86e363dc3b50bfd50a1f315934583fbda673ab8d Mon Sep 17 00:00:00 2001 From: WANG Cong Date: Tue, 26 May 2015 16:08:48 -0700 Subject: [PATCH] net_sched: invoke ->attach() after setting dev->qdisc For mq qdisc, we add per tx queue qdisc to root qdisc for display purpose, however, that happens too early, before the new dev->qdisc is finally set, this causes q->list points to an old root qdisc which is going to be freed right before assigning with a new one. Fix this by moving ->attach() after setting dev->qdisc. For the record, this fixes the following crash: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 975 at lib/list_debug.c:59 __list_del_entry+0x5a/0x98() list_del corruption. prev->next should be ffff8800d1998ae8, but was 6b6b6b6b6b6b6b6b CPU: 1 PID: 975 Comm: tc Not tainted 4.1.0-rc4+ #1019 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 0000000000000009 ffff8800d73fb928 ffffffff81a44e7f 0000000047574756 ffff8800d73fb978 ffff8800d73fb968 ffffffff810790da ffff8800cfc4cd20 ffffffff814e725b ffff8800d1998ae8 ffffffff82381250 0000000000000000 Call Trace: [] dump_stack+0x4c/0x65 [] warn_slowpath_common+0x9c/0xb6 [] ? __list_del_entry+0x5a/0x98 [] warn_slowpath_fmt+0x46/0x48 [] ? dev_graft_qdisc+0x5e/0x6a [] __list_del_entry+0x5a/0x98 [] list_del+0xe/0x2d [] qdisc_list_del+0x1e/0x20 [] qdisc_destroy+0x30/0xd6 [] qdisc_graft+0x11d/0x243 [] tc_get_qdisc+0x1a6/0x1d4 [] ? mark_lock+0x2e/0x226 [] rtnetlink_rcv_msg+0x181/0x194 [] ? rtnl_lock+0x17/0x19 [] ? rtnl_lock+0x17/0x19 [] ? __rtnl_unlock+0x17/0x17 [] netlink_rcv_skb+0x4d/0x93 [] rtnetlink_rcv+0x26/0x2d [] netlink_unicast+0xcb/0x150 [] ? might_fault+0x59/0xa9 [] netlink_sendmsg+0x4fa/0x51c [] sock_sendmsg_nosec+0x12/0x1d [] sock_sendmsg+0x29/0x2e [] ___sys_sendmsg+0x1b4/0x23a [] ? native_sched_clock+0x35/0x37 [] ? sched_clock_local+0x12/0x72 [] ? sched_clock_cpu+0x9e/0xb7 [] ? current_kernel_time+0xe/0x32 [] ? lock_release_holdtime.part.29+0x71/0x7f [] ? read_seqcount_begin.constprop.27+0x5f/0x76 [] ? trace_hardirqs_on_caller+0x17d/0x199 [] ? __fget_light+0x50/0x78 [] __sys_sendmsg+0x42/0x60 [] SyS_sendmsg+0x12/0x1c [] system_call_fastpath+0x12/0x6f ---[ end trace ef29d3fb28e97ae7 ]--- For long term, we probably need to clean up the qdisc_graft() code in case it hides other bugs like this. Fixes: 95dc19299f74 ("pkt_sched: give visibility to mq slave qdiscs") Cc: Jamal Hadi Salim Signed-off-by: Cong Wang Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- net/sched/sch_api.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c index ad9eed70bc8f..1e1c89e51a11 100644 --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -815,10 +815,8 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, if (dev->flags & IFF_UP) dev_deactivate(dev); - if (new && new->ops->attach) { - new->ops->attach(new); - num_q = 0; - } + if (new && new->ops->attach) + goto skip; for (i = 0; i < num_q; i++) { struct netdev_queue *dev_queue = dev_ingress_queue(dev); @@ -834,12 +832,16 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, qdisc_destroy(old); } +skip: if (!ingress) { notify_and_destroy(net, skb, n, classid, dev->qdisc, new); if (new && !new->ops->attach) atomic_inc(&new->refcnt); dev->qdisc = new ? : &noop_qdisc; + + if (new && new->ops->attach) + new->ops->attach(new); } else { notify_and_destroy(net, skb, n, classid, old, new); } -- 2.39.5