======================================================
[ INFO: possible circular locking dependency detected ]
4.4.174+ #4 Not tainted
-------------------------------------------------------
syz-executor.5/6919 is trying to acquire lock:
 (&(&q->lock)->rlock){+.-...}, at: [<ffffffff823ba312>] spin_lock include/linux/spinlock.h:302 [inline]
 (&(&q->lock)->rlock){+.-...}, at: [<ffffffff823ba312>] ip_defrag+0x322/0x3b70 net/ipv4/ip_fragment.c:690

but task is already holding lock:
 (_xmit_NETROM){+.-...}, at: [<ffffffff822b1b58>] spin_lock include/linux/spinlock.h:302 [inline]
 (_xmit_NETROM){+.-...}, at: [<ffffffff822b1b58>] __netif_tx_lock include/linux/netdevice.h:3306 [inline]
 (_xmit_NETROM){+.-...}, at: [<ffffffff822b1b58>] sch_direct_xmit+0x238/0x700 net/sched/sch_generic.c:163

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff82717c98>] __raw_spin_lock include/linux/spinlock_api_smp.h:144 [inline]
       [<ffffffff82717c98>] _raw_spin_lock+0x38/0x50 kernel/locking/spinlock.c:151
       [<ffffffff8147f3a5>] spin_lock include/linux/spinlock.h:302 [inline]
       [<ffffffff8147f3a5>] get_partial_node.isra.0+0x45/0x490 mm/slub.c:1727
       [<ffffffff8147fb0a>] get_partial mm/slub.c:1834 [inline]
       [<ffffffff8147fb0a>] new_slab_objects mm/slub.c:2314 [inline]
       [<ffffffff8147fb0a>] ___slab_alloc.constprop.0+0x1ca/0x3e0 mm/slub.c:2476
       [<ffffffff8147fd70>] __slab_alloc.isra.0.constprop.0+0x50/0xa0 mm/slub.c:2518
       [<ffffffff8148364e>] slab_alloc_node mm/slub.c:2581 [inline]
       [<ffffffff8148364e>] slab_alloc mm/slub.c:2623 [inline]
       [<ffffffff8148364e>] __kmalloc_track_caller+0x23e/0x2e0 mm/slub.c:4153
       [<ffffffff81409597>] kmemdup+0x27/0x60 mm/util.c:115
       [<ffffffff822136fe>] scm_fp_dup+0x5e/0x220 net/core/scm.c:339
       [<ffffffff8258dd9c>] unix_stream_read_generic+0xbfc/0x1fa0 net/unix/af_unix.c:2431
       [<ffffffff8258f403>] unix_stream_recvmsg+0xc3/0x100 net/unix/af_unix.c:2481
       [<ffffffff821d2a25>] sock_recvmsg_nosec+0x75/0x90 net/socket.c:740
       [<ffffffff821da5e7>] ___sys_recvmsg+0x257/0x530 net/socket.c:2129
       [<ffffffff821dd8c3>] __sys_recvmmsg+0x223/0x6f0 net/socket.c:2237
       [<ffffffff821ddf08>] SYSC_recvmmsg net/socket.c:2311 [inline]
       [<ffffffff821ddf08>] SyS_recvmmsg+0x178/0x1a0 net/socket.c:2300
       [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81202d86>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff81202d86>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff81202d86>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff81202d86>] __lock_acquire+0x37d6/0x4f50 kernel/locking/lockdep.c:3213
       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff82717c98>] __raw_spin_lock include/linux/spinlock_api_smp.h:144 [inline]
       [<ffffffff82717c98>] _raw_spin_lock+0x38/0x50 kernel/locking/spinlock.c:151
       [<ffffffff823ba312>] spin_lock include/linux/spinlock.h:302 [inline]
       [<ffffffff823ba312>] ip_defrag+0x322/0x3b70 net/ipv4/ip_fragment.c:690
       [<ffffffff823bdf36>] ip_check_defrag net/ipv4/ip_fragment.c:738 [inline]
       [<ffffffff823bdf36>] ip_check_defrag+0x3d6/0x5b0 net/ipv4/ip_fragment.c:705
       [<ffffffff826dfb3e>] packet_rcv_fanout+0x51e/0x5f0 net/packet/af_packet.c:1458
       [<ffffffff82244b38>] deliver_skb net/core/dev.c:1842 [inline]
       [<ffffffff82244b38>] dev_queue_xmit_nit net/core/dev.c:1898 [inline]
       [<ffffffff82244b38>] xmit_one net/core/dev.c:2777 [inline]
       [<ffffffff82244b38>] dev_hard_start_xmit+0x288/0x11e0 net/core/dev.c:2797
       [<ffffffff822b1bd6>] sch_direct_xmit+0x2b6/0x700 net/sched/sch_generic.c:165
       [<ffffffff82246aa4>] __dev_xmit_skb net/core/dev.c:2979 [inline]
       [<ffffffff82246aa4>] __dev_queue_xmit+0xd24/0x1bb0 net/core/dev.c:3197
       [<ffffffff82247948>] dev_queue_xmit+0x18/0x20 net/core/dev.c:3263
       [<ffffffff823c5962>] neigh_hh_output include/net/neighbour.h:486 [inline]
       [<ffffffff823c5962>] dst_neigh_output include/net/dst.h:459 [inline]
       [<ffffffff823c5962>] ip_finish_output2+0xbf2/0x1280 net/ipv4/ip_output.c:213
       [<ffffffff823c805c>] ip_do_fragment+0x187c/0x1f70 net/ipv4/ip_output.c:635
       [<ffffffff823cbd7b>] ip_fragment.constprop.0+0x14b/0x200 net/ipv4/ip_output.c:505
       [<ffffffff823cc1e9>] ip_finish_output+0x3b9/0xc60 net/ipv4/ip_output.c:286
       [<ffffffff823cf9f1>] NF_HOOK_COND include/linux/netfilter.h:240 [inline]
       [<ffffffff823cf9f1>] ip_mc_output+0x251/0xae0 net/ipv4/ip_output.c:347
       [<ffffffff823cd21c>] dst_output include/net/dst.h:498 [inline]
       [<ffffffff823cd21c>] ip_local_out+0x9c/0x180 net/ipv4/ip_output.c:119
       [<ffffffff823d300e>] ip_send_skb+0x3e/0xc0 net/ipv4/ip_output.c:1453
       [<ffffffff82478ded>] udp_send_skb+0x4fd/0xc70 net/ipv4/udp.c:842
       [<ffffffff824795ae>] udp_push_pending_frames+0x4e/0xe0 net/ipv4/udp.c:870
       [<ffffffff8248084e>] udp_sendpage+0x2ae/0x410 net/ipv4/udp.c:1183
       [<ffffffff824aa083>] inet_sendpage+0x223/0x520 net/ipv4/af_inet.c:772
       [<ffffffff821d81b5>] kernel_sendpage+0x95/0xf0 net/socket.c:3320
       [<ffffffff821d829b>] sock_sendpage+0x8b/0xc0 net/socket.c:793
       [<ffffffff81530f1d>] pipe_to_sendpage+0x28d/0x3d0 fs/splice.c:724
       [<ffffffff81533b6e>] splice_from_pipe_feed fs/splice.c:776 [inline]
       [<ffffffff81533b6e>] __splice_from_pipe+0x37e/0x7a0 fs/splice.c:901
       [<ffffffff81536be8>] splice_from_pipe+0x108/0x170 fs/splice.c:936
       [<ffffffff81536c8c>] generic_splice_sendpage+0x3c/0x50 fs/splice.c:1109
       [<ffffffff81537d31>] do_splice_from fs/splice.c:1128 [inline]
       [<ffffffff81537d31>] do_splice fs/splice.c:1404 [inline]
       [<ffffffff81537d31>] SYSC_splice fs/splice.c:1707 [inline]
       [<ffffffff81537d31>] SyS_splice+0xd71/0x13a0 fs/splice.c:1690
       [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(_xmit_NETROM);
                               lock(&(&q->lock)->rlock);
                               lock(_xmit_NETROM);
  lock(&(&q->lock)->rlock);

 *** DEADLOCK ***

6 locks held by syz-executor.5/6919:
 #0:  (&pipe->mutex/1){+.+.+.}, at: [<ffffffff814af8b3>] pipe_lock_nested fs/pipe.c:65 [inline]
 #0:  (&pipe->mutex/1){+.+.+.}, at: [<ffffffff814af8b3>] pipe_lock+0x63/0x80 fs/pipe.c:73
 #1:  (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff824806d2>] lock_sock include/net/sock.h:1497 [inline]
 #1:  (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff824806d2>] udp_sendpage+0x132/0x410 net/ipv4/udp.c:1160
 #2:  (rcu_read_lock_bh){......}, at: [<ffffffff823c4f7b>] ip_finish_output2+0x20b/0x1280 net/ipv4/ip_output.c:193
 #3:  (rcu_read_lock_bh){......}, at: [<ffffffff82245f57>] __dev_queue_xmit+0x1d7/0x1bb0 net/core/dev.c:3161
 #4:  (_xmit_NETROM){+.-...}, at: [<ffffffff822b1b58>] spin_lock include/linux/spinlock.h:302 [inline]
 #4:  (_xmit_NETROM){+.-...}, at: [<ffffffff822b1b58>] __netif_tx_lock include/linux/netdevice.h:3306 [inline]
 #4:  (_xmit_NETROM){+.-...}, at: [<ffffffff822b1b58>] sch_direct_xmit+0x238/0x700 net/sched/sch_generic.c:163
 #5:  (rcu_read_lock){......}, at: [<ffffffff82244963>] xmit_one net/core/dev.c:2776 [inline]
 #5:  (rcu_read_lock){......}, at: [<ffffffff82244963>] dev_hard_start_xmit+0xb3/0x11e0 net/core/dev.c:2797

stack backtrace:
CPU: 0 PID: 6919 Comm: syz-executor.5 Not tainted 4.4.174+ #4
 0000000000000000 91177751d9bd5072 ffff8800b4cbed40 ffffffff81aad1a1
 ffffffff84057a80 ffff8801d6ae5f00 ffffffff83aee000 ffffffff83ad5370
 ffffffff83aee000 ffff8800b4cbed90 ffffffff813abcda ffff8800b4cbee70
Call Trace:
 [<ffffffff81aad1a1>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81aad1a1>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<ffffffff813abcda>] print_circular_bug.cold+0x2f7/0x44e kernel/locking/lockdep.c:1226
 [<ffffffff81202d86>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff81202d86>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff81202d86>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff81202d86>] __lock_acquire+0x37d6/0x4f50 kernel/locking/lockdep.c:3213
 [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff82717c98>] __raw_spin_lock include/linux/spinlock_api_smp.h:144 [inline]
 [<ffffffff82717c98>] _raw_spin_lock+0x38/0x50 kernel/locking/spinlock.c:151
 [<ffffffff823ba312>] spin_lock include/linux/spinlock.h:302 [inline]
 [<ffffffff823ba312>] ip_defrag+0x322/0x3b70 net/ipv4/ip_fragment.c:690
 [<ffffffff823bdf36>] ip_check_defrag net/ipv4/ip_fragment.c:738 [inline]
 [<ffffffff823bdf36>] ip_check_defrag+0x3d6/0x5b0 net/ipv4/ip_fragment.c:705
 [<ffffffff826dfb3e>] packet_rcv_fanout+0x51e/0x5f0 net/packet/af_packet.c:1458
 [<ffffffff82244b38>] deliver_skb net/core/dev.c:1842 [inline]
 [<ffffffff82244b38>] dev_queue_xmit_nit net/core/dev.c:1898 [inline]
 [<ffffffff82244b38>] xmit_one net/core/dev.c:2777 [inline]
 [<ffffffff82244b38>] dev_hard_start_xmit+0x288/0x11e0 net/core/dev.c:2797
 [<ffffffff822b1bd6>] sch_direct_xmit+0x2b6/0x700 net/sched/sch_generic.c:165
 [<ffffffff82246aa4>] __dev_xmit_skb net/core/dev.c:2979 [inline]
 [<ffffffff82246aa4>] __dev_queue_xmit+0xd24/0x1bb0 net/core/dev.c:3197
 [<ffffffff82247948>] dev_queue_xmit+0x18/0x20 net/core/dev.c:3263
 [<ffffffff823c5962>] neigh_hh_output include/net/neighbour.h:486 [inline]
 [<ffffffff823c5962>] dst_neigh_output include/net/dst.h:459 [inline]
 [<ffffffff823c5962>] ip_finish_output2+0xbf2/0x1280 net/ipv4/ip_output.c:213
 [<ffffffff823c805c>] ip_do_fragment+0x187c/0x1f70 net/ipv4/ip_output.c:635
 [<ffffffff823cbd7b>] ip_fragment.constprop.0+0x14b/0x200 net/ipv4/ip_output.c:505
 [<ffffffff823cc1e9>] ip_finish_output+0x3b9/0xc60 net/ipv4/ip_output.c:286
 [<ffffffff823cf9f1>] NF_HOOK_COND include/linux/netfilter.h:240 [inline]
 [<ffffffff823cf9f1>] ip_mc_output+0x251/0xae0 net/ipv4/ip_output.c:347
 [<ffffffff823cd21c>] dst_output include/net/dst.h:498 [inline]
 [<ffffffff823cd21c>] ip_local_out+0x9c/0x180 net/ipv4/ip_output.c:119
 [<ffffffff823d300e>] ip_send_skb+0x3e/0xc0 net/ipv4/ip_output.c:1453
 [<ffffffff82478ded>] udp_send_skb+0x4fd/0xc70 net/ipv4/udp.c:842
 [<ffffffff824795ae>] udp_push_pending_frames+0x4e/0xe0 net/ipv4/udp.c:870
 [<ffffffff8248084e>] udp_sendpage+0x2ae/0x410 net/ipv4/udp.c:1183
 [<ffffffff824aa083>] inet_sendpage+0x223/0x520 net/ipv4/af_inet.c:772
 [<ffffffff821d81b5>] kernel_sendpage+0x95/0xf0 net/socket.c:3320
 [<ffffffff821d829b>] sock_sendpage+0x8b/0xc0 net/socket.c:793
 [<ffffffff81530f1d>] pipe_to_sendpage+0x28d/0x3d0 fs/splice.c:724
 [<ffffffff81533b6e>] splice_from_pipe_feed fs/splice.c:776 [inline]
 [<ffffffff81533b6e>] __splice_from_pipe+0x37e/0x7a0 fs/splice.c:901
 [<ffffffff81536be8>] splice_from_pipe+0x108/0x170 fs/splice.c:936
 [<ffffffff81536c8c>] generic_splice_sendpage+0x3c/0x50 fs/splice.c:1109
 [<ffffffff81537d31>] do_splice_from fs/splice.c:1128 [inline]
 [<ffffffff81537d31>] do_splice fs/splice.c:1404 [inline]
 [<ffffffff81537d31>] SYSC_splice fs/splice.c:1707 [inline]
 [<ffffffff81537d31>] SyS_splice+0xd71/0x13a0 fs/splice.c:1690
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a