Re: net: deadlock between ip_expire/sch_direct_xmit

From: Paolo Abeni
Date: Tue Mar 14 2017 - 11:05:26 EST

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In reply to: Cong Wang: "Re: net: deadlock between ip_expire/sch_direct_xmit"
Next in thread: Eric Dumazet: "Re: net: deadlock between ip_expire/sch_direct_xmit"
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On Tue, 2017-03-14 at 07:41 -0700, Eric Dumazet wrote:
> On Tue, 2017-03-14 at 14:31 +0100, Dmitry Vyukov wrote:
> > Hello,
> >
> > I've got the following deadlock report while running syzkaller fuzzer
> > on net-next/92cd12c5ed432c5eebd2462d666772a8d8442c3b:
> >
> >
> > [ INFO: possible circular locking dependency detected ]
> > 4.10.0+ #29 Not tainted
> > -------------------------------------------------------
> > modprobe/12392 is trying to acquire lock:
> > (_xmit_ETHER#2){+.-...}, at: [<ffffffff837a8182>] spin_lock
> > include/linux/spinlock.h:299 [inline]
> > (_xmit_ETHER#2){+.-...}, at: [<ffffffff837a8182>] __netif_tx_lock
> > include/linux/netdevice.h:3486 [inline]
> > (_xmit_ETHER#2){+.-...}, at: [<ffffffff837a8182>]
> > sch_direct_xmit+0x282/0x6d0 net/sched/sch_generic.c:180
> >
> > but task is already holding lock:
> > (&(&q->lock)->rlock){+.-...}, at: [<ffffffff8389a4d1>] spin_lock
> > include/linux/spinlock.h:299 [inline]
> > (&(&q->lock)->rlock){+.-...}, at: [<ffffffff8389a4d1>]
> > ip_expire+0x51/0x6c0 net/ipv4/ip_fragment.c:201
> >
> > which lock already depends on the new lock.
> >
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #1 (&(&q->lock)->rlock){+.-...}:
> > validate_chain kernel/locking/lockdep.c:2267 [inline]
> > __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> > lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> > __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> > _raw_spin_lock+0x33/0x50 kernel/locking/spinlock.c:151
> > spin_lock include/linux/spinlock.h:299 [inline]
> > ip_defrag+0x3a2/0x4130 net/ipv4/ip_fragment.c:669
> > ip_check_defrag+0x4e3/0x8b0 net/ipv4/ip_fragment.c:713
> > packet_rcv_fanout+0x282/0x800 net/packet/af_packet.c:1459
> > deliver_skb net/core/dev.c:1834 [inline]
> > dev_queue_xmit_nit+0x294/0xa90 net/core/dev.c:1890
> > xmit_one net/core/dev.c:2903 [inline]
> > dev_hard_start_xmit+0x16b/0xab0 net/core/dev.c:2923
> > sch_direct_xmit+0x31f/0x6d0 net/sched/sch_generic.c:182
> > __dev_xmit_skb net/core/dev.c:3092 [inline]
> > __dev_queue_xmit+0x13e5/0x1e60 net/core/dev.c:3358
> > dev_queue_xmit+0x17/0x20 net/core/dev.c:3423
> > neigh_resolve_output+0x6b9/0xb10 net/core/neighbour.c:1308
> > neigh_output include/net/neighbour.h:478 [inline]
> > ip_finish_output2+0x8b8/0x15a0 net/ipv4/ip_output.c:228
> > ip_do_fragment+0x1d93/0x2720 net/ipv4/ip_output.c:672
> > ip_fragment.constprop.54+0x145/0x200 net/ipv4/ip_output.c:545
> > ip_finish_output+0x82d/0xe10 net/ipv4/ip_output.c:314
> > NF_HOOK_COND include/linux/netfilter.h:246 [inline]
> > ip_output+0x1f0/0x7a0 net/ipv4/ip_output.c:404
> > dst_output include/net/dst.h:486 [inline]
> > ip_local_out+0x95/0x170 net/ipv4/ip_output.c:124
> > ip_send_skb+0x3c/0xc0 net/ipv4/ip_output.c:1492
> > ip_push_pending_frames+0x64/0x80 net/ipv4/ip_output.c:1512
> > raw_sendmsg+0x26de/0x3a00 net/ipv4/raw.c:655
> > inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:761
> > sock_sendmsg_nosec net/socket.c:633 [inline]
> > sock_sendmsg+0xca/0x110 net/socket.c:643
> > ___sys_sendmsg+0x4a3/0x9f0 net/socket.c:1985
> > __sys_sendmmsg+0x25c/0x750 net/socket.c:2075
> > SYSC_sendmmsg net/socket.c:2106 [inline]
> > SyS_sendmmsg+0x35/0x60 net/socket.c:2101
> > do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281
> > return_from_SYSCALL_64+0x0/0x7a
> >
> > -> #0 (_xmit_ETHER#2){+.-...}:
> > check_prev_add kernel/locking/lockdep.c:1830 [inline]
> > check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1940
> > validate_chain kernel/locking/lockdep.c:2267 [inline]
> > __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> > lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> > __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> > _raw_spin_lock+0x33/0x50 kernel/locking/spinlock.c:151
> > spin_lock include/linux/spinlock.h:299 [inline]
> > __netif_tx_lock include/linux/netdevice.h:3486 [inline]
> > sch_direct_xmit+0x282/0x6d0 net/sched/sch_generic.c:180
> > __dev_xmit_skb net/core/dev.c:3092 [inline]
> > __dev_queue_xmit+0x13e5/0x1e60 net/core/dev.c:3358
> > dev_queue_xmit+0x17/0x20 net/core/dev.c:3423
> > neigh_hh_output include/net/neighbour.h:468 [inline]
> > neigh_output include/net/neighbour.h:476 [inline]
> > ip_finish_output2+0xf6c/0x15a0 net/ipv4/ip_output.c:228
> > ip_finish_output+0xa29/0xe10 net/ipv4/ip_output.c:316
> > NF_HOOK_COND include/linux/netfilter.h:246 [inline]
> > ip_output+0x1f0/0x7a0 net/ipv4/ip_output.c:404
> > dst_output include/net/dst.h:486 [inline]
> > ip_local_out+0x95/0x170 net/ipv4/ip_output.c:124
> > ip_send_skb+0x3c/0xc0 net/ipv4/ip_output.c:1492
> > ip_push_pending_frames+0x64/0x80 net/ipv4/ip_output.c:1512
> > icmp_push_reply+0x372/0x4d0 net/ipv4/icmp.c:394
> > icmp_send+0x156c/0x1c80 net/ipv4/icmp.c:754
> > ip_expire+0x40e/0x6c0 net/ipv4/ip_fragment.c:239
> > call_timer_fn+0x241/0x820 kernel/time/timer.c:1268
> > expire_timers kernel/time/timer.c:1307 [inline]
> > __run_timers+0x960/0xcf0 kernel/time/timer.c:1601
> > run_timer_softirq+0x21/0x80 kernel/time/timer.c:1614
> > __do_softirq+0x31f/0xbe7 kernel/softirq.c:284
> > invoke_softirq kernel/softirq.c:364 [inline]
> > irq_exit+0x1cc/0x200 kernel/softirq.c:405
> > exiting_irq arch/x86/include/asm/apic.h:657 [inline]
> > smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:962
> > apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:707
> > __read_once_size include/linux/compiler.h:254 [inline]
> > atomic_read arch/x86/include/asm/atomic.h:26 [inline]
> > rcu_dynticks_curr_cpu_in_eqs kernel/rcu/tree.c:350 [inline]
> > __rcu_is_watching kernel/rcu/tree.c:1133 [inline]
> > rcu_is_watching+0x83/0x110 kernel/rcu/tree.c:1147
> > rcu_read_lock_held+0x87/0xc0 kernel/rcu/update.c:293
> > radix_tree_deref_slot include/linux/radix-tree.h:238 [inline]
> > filemap_map_pages+0x6d4/0x1570 mm/filemap.c:2335
> > do_fault_around mm/memory.c:3231 [inline]
> > do_read_fault mm/memory.c:3265 [inline]
> > do_fault+0xbd5/0x2080 mm/memory.c:3370
> > handle_pte_fault mm/memory.c:3600 [inline]
> > __handle_mm_fault+0x1062/0x2cb0 mm/memory.c:3714
> > handle_mm_fault+0x1e2/0x480 mm/memory.c:3751
> > __do_page_fault+0x4f6/0xb60 arch/x86/mm/fault.c:1397
> > do_page_fault+0x54/0x70 arch/x86/mm/fault.c:1460
> > page_fault+0x28/0x30 arch/x86/entry/entry_64.S:1011
> >
> > other info that might help us debug this:
> >
> > Possible unsafe locking scenario:
> >
> > CPU0 CPU1
> > ---- ----
> > lock(&(&q->lock)->rlock);
> > lock(_xmit_ETHER#2);
> > lock(&(&q->lock)->rlock);
> > lock(_xmit_ETHER#2);
> >
> > *** DEADLOCK ***
> >
> > 10 locks held by modprobe/12392:
> > #0: (&mm->mmap_sem){++++++}, at: [<ffffffff81329758>]
> > __do_page_fault+0x2b8/0xb60 arch/x86/mm/fault.c:1336
> > #1: (rcu_read_lock){......}, at: [<ffffffff8188cab6>]
> > filemap_map_pages+0x1e6/0x1570 mm/filemap.c:2324
> > #2: (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff81984a78>]
> > spin_lock include/linux/spinlock.h:299 [inline]
> > #2: (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff81984a78>]
> > pte_alloc_one_map mm/memory.c:2944 [inline]
> > #2: (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff81984a78>]
> > alloc_set_pte+0x13b8/0x1b90 mm/memory.c:3072
> > #3: (((&q->timer))){+.-...}, at: [<ffffffff81627e72>]
> > lockdep_copy_map include/linux/lockdep.h:175 [inline]
> > #3: (((&q->timer))){+.-...}, at: [<ffffffff81627e72>]
> > call_timer_fn+0x1c2/0x820 kernel/time/timer.c:1258
> > #4: (&(&q->lock)->rlock){+.-...}, at: [<ffffffff8389a4d1>] spin_lock
> > include/linux/spinlock.h:299 [inline]
> > #4: (&(&q->lock)->rlock){+.-...}, at: [<ffffffff8389a4d1>]
> > ip_expire+0x51/0x6c0 net/ipv4/ip_fragment.c:201
> > #5: (rcu_read_lock){......}, at: [<ffffffff8389a633>]
> > ip_expire+0x1b3/0x6c0 net/ipv4/ip_fragment.c:216
> > #6: (slock-AF_INET){+.-...}, at: [<ffffffff839b3313>] spin_trylock
> > include/linux/spinlock.h:309 [inline]
> > #6: (slock-AF_INET){+.-...}, at: [<ffffffff839b3313>] icmp_xmit_lock
> > net/ipv4/icmp.c:219 [inline]
> > #6: (slock-AF_INET){+.-...}, at: [<ffffffff839b3313>]
> > icmp_send+0x803/0x1c80 net/ipv4/icmp.c:681
> > #7: (rcu_read_lock_bh){......}, at: [<ffffffff838ab9a1>]
> > ip_finish_output2+0x2c1/0x15a0 net/ipv4/ip_output.c:198
> > #8: (rcu_read_lock_bh){......}, at: [<ffffffff836d1dee>]
> > __dev_queue_xmit+0x23e/0x1e60 net/core/dev.c:3324
> > #9: (dev->qdisc_running_key ?: &qdisc_running_key){+.....}, at:
> > [<ffffffff836d3a27>] dev_queue_xmit+0x17/0x20 net/core/dev.c:3423
> >
> > stack backtrace:
> > CPU: 0 PID: 12392 Comm: modprobe Not tainted 4.10.0+ #29
> > Hardware name: Google Google Compute Engine/Google Compute Engine,
> > BIOS Google 01/01/2011
> > Call Trace:
> > <IRQ>
> > __dump_stack lib/dump_stack.c:16 [inline]
> > dump_stack+0x2ee/0x3ef lib/dump_stack.c:52
> > print_circular_bug+0x307/0x3b0 kernel/locking/lockdep.c:1204
> > check_prev_add kernel/locking/lockdep.c:1830 [inline]
> > check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1940
> > validate_chain kernel/locking/lockdep.c:2267 [inline]
> > __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> > lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> > __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> > _raw_spin_lock+0x33/0x50 kernel/locking/spinlock.c:151
> > spin_lock include/linux/spinlock.h:299 [inline]
> > __netif_tx_lock include/linux/netdevice.h:3486 [inline]
> > sch_direct_xmit+0x282/0x6d0 net/sched/sch_generic.c:180
> > __dev_xmit_skb net/core/dev.c:3092 [inline]
> > __dev_queue_xmit+0x13e5/0x1e60 net/core/dev.c:3358
> > dev_queue_xmit+0x17/0x20 net/core/dev.c:3423
> > neigh_hh_output include/net/neighbour.h:468 [inline]
> > neigh_output include/net/neighbour.h:476 [inline]
> > ip_finish_output2+0xf6c/0x15a0 net/ipv4/ip_output.c:228
> > ip_finish_output+0xa29/0xe10 net/ipv4/ip_output.c:316
> > NF_HOOK_COND include/linux/netfilter.h:246 [inline]
> > ip_output+0x1f0/0x7a0 net/ipv4/ip_output.c:404
> > dst_output include/net/dst.h:486 [inline]
> > ip_local_out+0x95/0x170 net/ipv4/ip_output.c:124
> > ip_send_skb+0x3c/0xc0 net/ipv4/ip_output.c:1492
> > ip_push_pending_frames+0x64/0x80 net/ipv4/ip_output.c:1512
> > icmp_push_reply+0x372/0x4d0 net/ipv4/icmp.c:394
> > icmp_send+0x156c/0x1c80 net/ipv4/icmp.c:754
> > ip_expire+0x40e/0x6c0 net/ipv4/ip_fragment.c:239
> > call_timer_fn+0x241/0x820 kernel/time/timer.c:1268
> > expire_timers kernel/time/timer.c:1307 [inline]
> > __run_timers+0x960/0xcf0 kernel/time/timer.c:1601
> > run_timer_softirq+0x21/0x80 kernel/time/timer.c:1614
> > __do_softirq+0x31f/0xbe7 kernel/softirq.c:284
> > invoke_softirq kernel/softirq.c:364 [inline]
> > irq_exit+0x1cc/0x200 kernel/softirq.c:405
> > exiting_irq arch/x86/include/asm/apic.h:657 [inline]
> > smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:962
> > apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:707
> > RIP: 0010:__read_once_size include/linux/compiler.h:254 [inline]
> > RIP: 0010:atomic_read arch/x86/include/asm/atomic.h:26 [inline]
> > RIP: 0010:rcu_dynticks_curr_cpu_in_eqs kernel/rcu/tree.c:350 [inline]
> > RIP: 0010:__rcu_is_watching kernel/rcu/tree.c:1133 [inline]
> > RIP: 0010:rcu_is_watching+0x83/0x110 kernel/rcu/tree.c:1147
> > RSP: 0000:ffff8801c391f120 EFLAGS: 00000a03 ORIG_RAX: ffffffffffffff10
> > RAX: dffffc0000000000 RBX: ffff8801c391f148 RCX: 0000000000000000
> > RDX: 0000000000000000 RSI: 000055edd4374000 RDI: ffff8801dbe1ae0c
> > RBP: ffff8801c391f1a0 R08: 0000000000000002 R09: 0000000000000000
> > R10: dffffc0000000000 R11: 0000000000000002 R12: 1ffff10038723e25
> > R13: ffff8801dbe1ae00 R14: ffff8801c391f680 R15: dffffc0000000000
> > </IRQ>
> > rcu_read_lock_held+0x87/0xc0 kernel/rcu/update.c:293
> > radix_tree_deref_slot include/linux/radix-tree.h:238 [inline]
> > filemap_map_pages+0x6d4/0x1570 mm/filemap.c:2335
> > do_fault_around mm/memory.c:3231 [inline]
> > do_read_fault mm/memory.c:3265 [inline]
> > do_fault+0xbd5/0x2080 mm/memory.c:3370
> > handle_pte_fault mm/memory.c:3600 [inline]
> > __handle_mm_fault+0x1062/0x2cb0 mm/memory.c:3714
> > handle_mm_fault+0x1e2/0x480 mm/memory.c:3751
> > __do_page_fault+0x4f6/0xb60 arch/x86/mm/fault.c:1397
> > do_page_fault+0x54/0x70 arch/x86/mm/fault.c:1460
> > page_fault+0x28/0x30 arch/x86/entry/entry_64.S:1011
> > RIP: 0033:0x7f83172f2786
> > RSP: 002b:00007fffe859ae80 EFLAGS: 00010293
> > RAX: 000055edd4373040 RBX: 00007f83175111c8 RCX: 000055edd4373238
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007f8317510970
> > RBP: 00007fffe859afd0 R08: 0000000000000009 R09: 0000000000000000
> > R10: 0000000000000064 R11: 0000000000000000 R12: 000055edd4373040
> > R13: 0000000000000000 R14: 00007fffe859afe8 R15: 0000000000000000
>
>
> This looks a false positive.
> An ICMP message can not be possibly fragmented.
> Following patch should fix the lockdep issue.
>
> diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
> index bbe7f72db9c157ba2d6c5292637c2f58ad39a123..b3cdeec85f1f2c612c362590e828f50596a5c247 100644
> --- a/net/ipv4/ip_fragment.c
> +++ b/net/ipv4/ip_fragment.c
> @@ -198,6 +198,7 @@ static void ip_expire(unsigned long arg)
> qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
> net = container_of(qp->q.net, struct net, ipv4.frags);
>
> + rcu_read_lock();
> spin_lock(&qp->q.lock);
>
> if (qp->q.flags & INET_FRAG_COMPLETE)
> @@ -207,7 +208,7 @@ static void ip_expire(unsigned long arg)
> __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
>
> if (!inet_frag_evicting(&qp->q)) {
> - struct sk_buff *head = qp->q.fragments;
> + struct sk_buff *clone, *head = qp->q.fragments;
> const struct iphdr *iph;
> int err;
>
> @@ -216,32 +217,40 @@ static void ip_expire(unsigned long arg)
> if (!(qp->q.flags & INET_FRAG_FIRST_IN) || !qp->q.fragments)
> goto out;
>
> - rcu_read_lock();
> head->dev = dev_get_by_index_rcu(net, qp->iif);
> if (!head->dev)
> - goto out_rcu_unlock;
> + goto out;
> +
>
> /* skb has no dst, perform route lookup again */
> iph = ip_hdr(head);
> err = ip_route_input_noref(head, iph->daddr, iph->saddr,
> iph->tos, head->dev);
> if (err)
> - goto out_rcu_unlock;
> + goto out;
>
> /* Only an end host needs to send an ICMP
> * "Fragment Reassembly Timeout" message, per RFC792.
> */
> if (frag_expire_skip_icmp(qp->user) &&
> (skb_rtable(head)->rt_type != RTN_LOCAL))
> - goto out_rcu_unlock;
> + goto out;
> +
> + clone = skb_clone(head, GFP_ATOMIC);
>
> /* Send an ICMP "Fragment Reassembly Timeout" message. */
> - icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
> -out_rcu_unlock:
> - rcu_read_unlock();
> + if (clone) {
> + spin_unlock(&qp->q.lock);
> + icmp_send(clone, ICMP_TIME_EXCEEDED,
> + ICMP_EXC_FRAGTIME, 0);
> + consume_skb(clone);
> + goto out_rcu_unlock;
> + }
> }
> out:
> spin_unlock(&qp->q.lock);

I'm wondering if we really need to keep the fragment queue lock held
while sending the icmp packet ? we hold a reference to the struct, so
it can't be deleted, and AFAICS after ipq_kill() nobody else could
access/modify that queue.

That lock is there pretty much forever, but perhaps is only a leftover
and we can release it just after ipq_kill() ?

Paolo

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