net: sched: always disable bh when taking tcf_lock

Recently, ops->init() and ops->dump() of all actions were modified to
always obtain tcf_lock when accessing private action state. Actions that
don't depend on tcf_lock for synchronization with their data path use
non-bh locking API. However, tcf_lock is also used to protect rate
estimator stats in softirq context by timer callback.

Change ops->init() and ops->dump() of all actions to disable bh when using
tcf_lock to prevent deadlock reported by following lockdep warning:

[  105.470398] ================================
[  105.475014] WARNING: inconsistent lock state
[  105.479628] 4.18.0-rc8+ #664 Not tainted
[  105.483897] --------------------------------
[  105.488511] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[  105.494871] swapper/16/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
[  105.500449] 00000000f86c012e (&(&p->tcfa_lock)->rlock){+.?.}, at: est_fetch_counters+0x3c/0xa0
[  105.509696] {SOFTIRQ-ON-W} state was registered at:
[  105.514925]   _raw_spin_lock+0x2c/0x40
[  105.519022]   tcf_bpf_init+0x579/0x820 [act_bpf]
[  105.523990]   tcf_action_init_1+0x4e4/0x660
[  105.528518]   tcf_action_init+0x1ce/0x2d0
[  105.532880]   tcf_exts_validate+0x1d8/0x200
[  105.537416]   fl_change+0x55a/0x268b [cls_flower]
[  105.542469]   tc_new_tfilter+0x748/0xa20
[  105.546738]   rtnetlink_rcv_msg+0x56a/0x6d0
[  105.551268]   netlink_rcv_skb+0x18d/0x200
[  105.555628]   netlink_unicast+0x2d0/0x370
[  105.559990]   netlink_sendmsg+0x3b9/0x6a0
[  105.564349]   sock_sendmsg+0x6b/0x80
[  105.568271]   ___sys_sendmsg+0x4a1/0x520
[  105.572547]   __sys_sendmsg+0xd7/0x150
[  105.576655]   do_syscall_64+0x72/0x2c0
[  105.580757]   entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  105.586243] irq event stamp: 489296
[  105.590084] hardirqs last  enabled at (489296): [<ffffffffb507e639>] _raw_spin_unlock_irq+0x29/0x40
[  105.599765] hardirqs last disabled at (489295): [<ffffffffb507e745>] _raw_spin_lock_irq+0x15/0x50
[  105.609277] softirqs last  enabled at (489292): [<ffffffffb413a6a3>] irq_enter+0x83/0xa0
[  105.618001] softirqs last disabled at (489293): [<ffffffffb413a800>] irq_exit+0x140/0x190
[  105.626813]
               other info that might help us debug this:
[  105.633976]  Possible unsafe locking scenario:

[  105.640526]        CPU0
[  105.643325]        ----
[  105.646125]   lock(&(&p->tcfa_lock)->rlock);
[  105.650747]   <Interrupt>
[  105.653717]     lock(&(&p->tcfa_lock)->rlock);
[  105.658514]
                *** DEADLOCK ***

[  105.665349] 1 lock held by swapper/16/0:
[  105.669629]  #0: 00000000a640ad99 ((&est->timer)){+.-.}, at: call_timer_fn+0x10b/0x550
[  105.678200]
               stack backtrace:
[  105.683194] CPU: 16 PID: 0 Comm: swapper/16 Not tainted 4.18.0-rc8+ #664
[  105.690249] Hardware name: Supermicro SYS-2028TP-DECR/X10DRT-P, BIOS 2.0b 03/30/2017
[  105.698626] Call Trace:
[  105.701421]  <IRQ>
[  105.703791]  dump_stack+0x92/0xeb
[  105.707461]  print_usage_bug+0x336/0x34c
[  105.711744]  mark_lock+0x7c9/0x980
[  105.715500]  ? print_shortest_lock_dependencies+0x2e0/0x2e0
[  105.721424]  ? check_usage_forwards+0x230/0x230
[  105.726315]  __lock_acquire+0x923/0x26f0
[  105.730597]  ? debug_show_all_locks+0x240/0x240
[  105.735478]  ? mark_lock+0x493/0x980
[  105.739412]  ? check_chain_key+0x140/0x1f0
[  105.743861]  ? __lock_acquire+0x836/0x26f0
[  105.748323]  ? lock_acquire+0x12e/0x290
[  105.752516]  lock_acquire+0x12e/0x290
[  105.756539]  ? est_fetch_counters+0x3c/0xa0
[  105.761084]  _raw_spin_lock+0x2c/0x40
[  105.765099]  ? est_fetch_counters+0x3c/0xa0
[  105.769633]  est_fetch_counters+0x3c/0xa0
[  105.773995]  est_timer+0x87/0x390
[  105.777670]  ? est_fetch_counters+0xa0/0xa0
[  105.782210]  ? lock_acquire+0x12e/0x290
[  105.786410]  call_timer_fn+0x161/0x550
[  105.790512]  ? est_fetch_counters+0xa0/0xa0
[  105.795055]  ? del_timer_sync+0xd0/0xd0
[  105.799249]  ? __lock_is_held+0x93/0x110
[  105.803531]  ? mark_held_locks+0x20/0xe0
[  105.807813]  ? _raw_spin_unlock_irq+0x29/0x40
[  105.812525]  ? est_fetch_counters+0xa0/0xa0
[  105.817069]  ? est_fetch_counters+0xa0/0xa0
[  105.821610]  run_timer_softirq+0x3c4/0x9f0
[  105.826064]  ? lock_acquire+0x12e/0x290
[  105.830257]  ? __bpf_trace_timer_class+0x10/0x10
[  105.835237]  ? __lock_is_held+0x25/0x110
[  105.839517]  __do_softirq+0x11d/0x7bf
[  105.843542]  irq_exit+0x140/0x190
[  105.847208]  smp_apic_timer_interrupt+0xac/0x3b0
[  105.852182]  apic_timer_interrupt+0xf/0x20
[  105.856628]  </IRQ>
[  105.859081] RIP: 0010:cpuidle_enter_state+0xd8/0x4d0
[  105.864395] Code: 46 ff 48 89 44 24 08 0f 1f 44 00 00 31 ff e8 cf ec 46 ff 80 7c 24 07 00 0f 85 1d 02 00 00 e8 9f 90 4b ff fb 66 0f 1f 44 00 00 <4c> 8b 6c 24 08 4d 29 fd 0f 80 36 03 00 00 4c 89 e8 48 ba cf f7 53
[  105.884288] RSP: 0018:ffff8803ad94fd20 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
[  105.892494] RAX: 0000000000000000 RBX: ffffe8fb300829c0 RCX: ffffffffb41e19e1
[  105.899988] RDX: 0000000000000007 RSI: dffffc0000000000 RDI: ffff8803ad9358ac
[  105.907503] RBP: ffffffffb6636300 R08: 0000000000000004 R09: 0000000000000000
[  105.914997] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000004
[  105.922487] R13: ffffffffb6636140 R14: ffffffffb66362d8 R15: 000000188d36091b
[  105.929988]  ? trace_hardirqs_on_caller+0x141/0x2d0
[  105.935232]  do_idle+0x28e/0x320
[  105.938817]  ? arch_cpu_idle_exit+0x40/0x40
[  105.943361]  ? mark_lock+0x8c1/0x980
[  105.947295]  ? _raw_spin_unlock_irqrestore+0x32/0x60
[  105.952619]  cpu_startup_entry+0xc2/0xd0
[  105.956900]  ? cpu_in_idle+0x20/0x20
[  105.960830]  ? _raw_spin_unlock_irqrestore+0x32/0x60
[  105.966146]  ? trace_hardirqs_on_caller+0x141/0x2d0
[  105.971391]  start_secondary+0x2b5/0x360
[  105.975669]  ? set_cpu_sibling_map+0x1330/0x1330
[  105.980654]  secondary_startup_64+0xa5/0xb0

Taking tcf_lock in sample action with bh disabled causes lockdep to issue a
warning regarding possible irq lock inversion dependency between tcf_lock,
and psample_groups_lock that is taken when holding tcf_lock in sample init:

[  162.108959]  Possible interrupt unsafe locking scenario:

[  162.116386]        CPU0                    CPU1
[  162.121277]        ----                    ----
[  162.126162]   lock(psample_groups_lock);
[  162.130447]                                local_irq_disable();
[  162.136772]                                lock(&(&p->tcfa_lock)->rlock);
[  162.143957]                                lock(psample_groups_lock);
[  162.150813]   <Interrupt>
[  162.153808]     lock(&(&p->tcfa_lock)->rlock);
[  162.158608]
                *** DEADLOCK ***

In order to prevent potential lock inversion dependency between tcf_lock
and psample_groups_lock, extract call to psample_group_get() from tcf_lock
protected section in sample action init function.

Fixes: 4e232818 ("net: sched: act_mirred: remove dependency on rtnl lock")
Fixes: 764e9a24 ("net: sched: act_vlan: remove dependency on rtnl lock")
Fixes: 729e0126 ("net: sched: act_tunnel_key: remove dependency on rtnl lock")
Fixes: d7728495 ("net: sched: act_sample: remove dependency on rtnl lock")
Fixes: e8917f43 ("net: sched: act_gact: remove dependency on rtnl lock")
Fixes: b6a2b971 ("net: sched: act_csum: remove dependency on rtnl lock")
Fixes: 2142236b ("net: sched: act_bpf: remove dependency on rtnl lock")
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_bpf.c

@@ -147,7 +147,7 @@ static int tcf_bpf_dump(struct sk_buff *skb, struct tc_action *act,
 	struct tcf_t tm;
 	int ret;
 
-	spin_lock(&prog->tcf_lock);
+	spin_lock_bh(&prog->tcf_lock);
 	opt.action = prog->tcf_action;
 	if (nla_put(skb, TCA_ACT_BPF_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
@@ -164,11 +164,11 @@ static int tcf_bpf_dump(struct sk_buff *skb, struct tc_action *act,
 			  TCA_ACT_BPF_PAD))
 		goto nla_put_failure;
 
-	spin_unlock(&prog->tcf_lock);
+	spin_unlock_bh(&prog->tcf_lock);
 	return skb->len;
 
 nla_put_failure:
-	spin_unlock(&prog->tcf_lock);
+	spin_unlock_bh(&prog->tcf_lock);
 	nlmsg_trim(skb, tp);
 	return -1;
 }
@@ -340,7 +340,7 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
 
 	prog = to_bpf(*act);
 
-	spin_lock(&prog->tcf_lock);
+	spin_lock_bh(&prog->tcf_lock);
 	if (res != ACT_P_CREATED)
 		tcf_bpf_prog_fill_cfg(prog, &old);
 
@@ -352,7 +352,7 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
 
 	prog->tcf_action = parm->action;
 	rcu_assign_pointer(prog->filter, cfg.filter);
-	spin_unlock(&prog->tcf_lock);
+	spin_unlock_bh(&prog->tcf_lock);
 
 	if (res == ACT_P_CREATED) {
 		tcf_idr_insert(tn, *act);

net/sched/act_csum.c

@@ -96,11 +96,11 @@ static int tcf_csum_init(struct net *net, struct nlattr *nla,
 	}
 	params_new->update_flags = parm->update_flags;
 
-	spin_lock(&p->tcf_lock);
+	spin_lock_bh(&p->tcf_lock);
 	p->tcf_action = parm->action;
 	rcu_swap_protected(p->params, params_new,
 			   lockdep_is_held(&p->tcf_lock));
-	spin_unlock(&p->tcf_lock);
+	spin_unlock_bh(&p->tcf_lock);
 
 	if (params_new)
 		kfree_rcu(params_new, rcu);
@@ -604,7 +604,7 @@ static int tcf_csum_dump(struct sk_buff *skb, struct tc_action *a, int bind,
 	};
 	struct tcf_t t;
 
-	spin_lock(&p->tcf_lock);
+	spin_lock_bh(&p->tcf_lock);
 	params = rcu_dereference_protected(p->params,
 					   lockdep_is_held(&p->tcf_lock));
 	opt.action = p->tcf_action;
@@ -616,12 +616,12 @@ static int tcf_csum_dump(struct sk_buff *skb, struct tc_action *a, int bind,
 	tcf_tm_dump(&t, &p->tcf_tm);
 	if (nla_put_64bit(skb, TCA_CSUM_TM, sizeof(t), &t, TCA_CSUM_PAD))
 		goto nla_put_failure;
-	spin_unlock(&p->tcf_lock);
+	spin_unlock_bh(&p->tcf_lock);
 
 	return skb->len;
 
 nla_put_failure:
-	spin_unlock(&p->tcf_lock);
+	spin_unlock_bh(&p->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }

net/sched/act_gact.c

@@ -113,7 +113,7 @@ static int tcf_gact_init(struct net *net, struct nlattr *nla,
 
 	gact = to_gact(*a);
 
-	spin_lock(&gact->tcf_lock);
+	spin_lock_bh(&gact->tcf_lock);
 	gact->tcf_action = parm->action;
 #ifdef CONFIG_GACT_PROB
 	if (p_parm) {
@@ -126,7 +126,7 @@ static int tcf_gact_init(struct net *net, struct nlattr *nla,
 		gact->tcfg_ptype   = p_parm->ptype;
 	}
 #endif
-	spin_unlock(&gact->tcf_lock);
+	spin_unlock_bh(&gact->tcf_lock);
 
 	if (ret == ACT_P_CREATED)
 		tcf_idr_insert(tn, *a);
@@ -183,7 +183,7 @@ static int tcf_gact_dump(struct sk_buff *skb, struct tc_action *a,
 	};
 	struct tcf_t t;
 
-	spin_lock(&gact->tcf_lock);
+	spin_lock_bh(&gact->tcf_lock);
 	opt.action = gact->tcf_action;
 	if (nla_put(skb, TCA_GACT_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
@@ -202,12 +202,12 @@ static int tcf_gact_dump(struct sk_buff *skb, struct tc_action *a,
 	tcf_tm_dump(&t, &gact->tcf_tm);
 	if (nla_put_64bit(skb, TCA_GACT_TM, sizeof(t), &t, TCA_GACT_PAD))
 		goto nla_put_failure;
-	spin_unlock(&gact->tcf_lock);
+	spin_unlock_bh(&gact->tcf_lock);
 
 	return skb->len;
 
 nla_put_failure:
-	spin_unlock(&gact->tcf_lock);
+	spin_unlock_bh(&gact->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }

net/sched/act_mirred.c

@@ -159,14 +159,14 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
 	}
 	m = to_mirred(*a);
 
-	spin_lock(&m->tcf_lock);
+	spin_lock_bh(&m->tcf_lock);
 	m->tcf_action = parm->action;
 	m->tcfm_eaction = parm->eaction;
 
 	if (parm->ifindex) {
 		dev = dev_get_by_index(net, parm->ifindex);
 		if (!dev) {
-			spin_unlock(&m->tcf_lock);
+			spin_unlock_bh(&m->tcf_lock);
 			tcf_idr_release(*a, bind);
 			return -ENODEV;
 		}
@@ -177,7 +177,7 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
 			dev_put(dev);
 		m->tcfm_mac_header_xmit = mac_header_xmit;
 	}
-	spin_unlock(&m->tcf_lock);
+	spin_unlock_bh(&m->tcf_lock);
 
 	if (ret == ACT_P_CREATED) {
 		spin_lock(&mirred_list_lock);
@@ -305,7 +305,7 @@ static int tcf_mirred_dump(struct sk_buff *skb, struct tc_action *a, int bind,
 	struct net_device *dev;
 	struct tcf_t t;
 
-	spin_lock(&m->tcf_lock);
+	spin_lock_bh(&m->tcf_lock);
 	opt.action = m->tcf_action;
 	opt.eaction = m->tcfm_eaction;
 	dev = tcf_mirred_dev_dereference(m);
@@ -318,12 +318,12 @@ static int tcf_mirred_dump(struct sk_buff *skb, struct tc_action *a, int bind,
 	tcf_tm_dump(&t, &m->tcf_tm);
 	if (nla_put_64bit(skb, TCA_MIRRED_TM, sizeof(t), &t, TCA_MIRRED_PAD))
 		goto nla_put_failure;
-	spin_unlock(&m->tcf_lock);
+	spin_unlock_bh(&m->tcf_lock);
 
 	return skb->len;
 
 nla_put_failure:
-	spin_unlock(&m->tcf_lock);
+	spin_unlock_bh(&m->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }
@@ -356,7 +356,7 @@ static int mirred_device_event(struct notifier_block *unused,
 	if (event == NETDEV_UNREGISTER) {
 		spin_lock(&mirred_list_lock);
 		list_for_each_entry(m, &mirred_list, tcfm_list) {
-			spin_lock(&m->tcf_lock);
+			spin_lock_bh(&m->tcf_lock);
 			if (tcf_mirred_dev_dereference(m) == dev) {
 				dev_put(dev);
 				/* Note : no rcu grace period necessary, as
@@ -364,7 +364,7 @@ static int mirred_device_event(struct notifier_block *unused,
 				 */
 				RCU_INIT_POINTER(m->tcfm_dev, NULL);
 			}
-			spin_unlock(&m->tcf_lock);
+			spin_unlock_bh(&m->tcf_lock);
 		}
 		spin_unlock(&mirred_list_lock);
 	}

net/sched/act_sample.c

@@ -44,6 +44,7 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,
 	struct nlattr *tb[TCA_SAMPLE_MAX + 1];
 	struct psample_group *psample_group;
 	struct tc_sample *parm;
+	u32 psample_group_num;
 	struct tcf_sample *s;
 	bool exists = false;
 	int ret, err;
@@ -78,25 +79,27 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,
 		tcf_idr_release(*a, bind);
 		return -EEXIST;
 	}
-	s = to_sample(*a);
 
-	spin_lock(&s->tcf_lock);
-	s->tcf_action = parm->action;
-	s->rate = nla_get_u32(tb[TCA_SAMPLE_RATE]);
-	s->psample_group_num = nla_get_u32(tb[TCA_SAMPLE_PSAMPLE_GROUP]);
-	psample_group = psample_group_get(net, s->psample_group_num);
+	psample_group_num = nla_get_u32(tb[TCA_SAMPLE_PSAMPLE_GROUP]);
+	psample_group = psample_group_get(net, psample_group_num);
 	if (!psample_group) {
-		spin_unlock(&s->tcf_lock);
 		tcf_idr_release(*a, bind);
 		return -ENOMEM;
 	}
+
+	s = to_sample(*a);
+
+	spin_lock_bh(&s->tcf_lock);
+	s->tcf_action = parm->action;
+	s->rate = nla_get_u32(tb[TCA_SAMPLE_RATE]);
+	s->psample_group_num = psample_group_num;
 	RCU_INIT_POINTER(s->psample_group, psample_group);
 
 	if (tb[TCA_SAMPLE_TRUNC_SIZE]) {
 		s->truncate = true;
 		s->trunc_size = nla_get_u32(tb[TCA_SAMPLE_TRUNC_SIZE]);
 	}
-	spin_unlock(&s->tcf_lock);
+	spin_unlock_bh(&s->tcf_lock);
 
 	if (ret == ACT_P_CREATED)
 		tcf_idr_insert(tn, *a);
@@ -183,7 +186,7 @@ static int tcf_sample_dump(struct sk_buff *skb, struct tc_action *a,
 	};
 	struct tcf_t t;
 
-	spin_lock(&s->tcf_lock);
+	spin_lock_bh(&s->tcf_lock);
 	opt.action = s->tcf_action;
 	if (nla_put(skb, TCA_SAMPLE_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
@@ -201,12 +204,12 @@ static int tcf_sample_dump(struct sk_buff *skb, struct tc_action *a,
 
 	if (nla_put_u32(skb, TCA_SAMPLE_PSAMPLE_GROUP, s->psample_group_num))
 		goto nla_put_failure;
-	spin_unlock(&s->tcf_lock);
+	spin_unlock_bh(&s->tcf_lock);
 
 	return skb->len;
 
 nla_put_failure:
-	spin_unlock(&s->tcf_lock);
+	spin_unlock_bh(&s->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }

net/sched/act_tunnel_key.c

@@ -354,11 +354,11 @@ static int tunnel_key_init(struct net *net, struct nlattr *nla,
 	params_new->tcft_action = parm->t_action;
 	params_new->tcft_enc_metadata = metadata;
 
-	spin_lock(&t->tcf_lock);
+	spin_lock_bh(&t->tcf_lock);
 	t->tcf_action = parm->action;
 	rcu_swap_protected(t->params, params_new,
 			   lockdep_is_held(&t->tcf_lock));
-	spin_unlock(&t->tcf_lock);
+	spin_unlock_bh(&t->tcf_lock);
 	if (params_new)
 		kfree_rcu(params_new, rcu);
 
@@ -485,7 +485,7 @@ static int tunnel_key_dump(struct sk_buff *skb, struct tc_action *a,
 	};
 	struct tcf_t tm;
 
-	spin_lock(&t->tcf_lock);
+	spin_lock_bh(&t->tcf_lock);
 	params = rcu_dereference_protected(t->params,
 					   lockdep_is_held(&t->tcf_lock));
 	opt.action   = t->tcf_action;
@@ -520,12 +520,12 @@ static int tunnel_key_dump(struct sk_buff *skb, struct tc_action *a,
 	if (nla_put_64bit(skb, TCA_TUNNEL_KEY_TM, sizeof(tm),
 			  &tm, TCA_TUNNEL_KEY_PAD))
 		goto nla_put_failure;
-	spin_unlock(&t->tcf_lock);
+	spin_unlock_bh(&t->tcf_lock);
 
 	return skb->len;
 
 nla_put_failure:
-	spin_unlock(&t->tcf_lock);
+	spin_unlock_bh(&t->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }

net/sched/act_vlan.c

@@ -213,10 +213,10 @@ static int tcf_vlan_init(struct net *net, struct nlattr *nla,
 	p->tcfv_push_prio = push_prio;
 	p->tcfv_push_proto = push_proto;
 
-	spin_lock(&v->tcf_lock);
+	spin_lock_bh(&v->tcf_lock);
 	v->tcf_action = parm->action;
 	rcu_swap_protected(v->vlan_p, p, lockdep_is_held(&v->tcf_lock));
-	spin_unlock(&v->tcf_lock);
+	spin_unlock_bh(&v->tcf_lock);
 
 	if (p)
 		kfree_rcu(p, rcu);
@@ -249,7 +249,7 @@ static int tcf_vlan_dump(struct sk_buff *skb, struct tc_action *a,
 	};
 	struct tcf_t t;
 
-	spin_lock(&v->tcf_lock);
+	spin_lock_bh(&v->tcf_lock);
 	opt.action = v->tcf_action;
 	p = rcu_dereference_protected(v->vlan_p, lockdep_is_held(&v->tcf_lock));
 	opt.v_action = p->tcfv_action;
@@ -268,12 +268,12 @@ static int tcf_vlan_dump(struct sk_buff *skb, struct tc_action *a,
 	tcf_tm_dump(&t, &v->tcf_tm);
 	if (nla_put_64bit(skb, TCA_VLAN_TM, sizeof(t), &t, TCA_VLAN_PAD))
 		goto nla_put_failure;
-	spin_unlock(&v->tcf_lock);
+	spin_unlock_bh(&v->tcf_lock);
 
 	return skb->len;
 
 nla_put_failure:
-	spin_unlock(&v->tcf_lock);
+	spin_unlock_bh(&v->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }