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BUG: KCSAN: data-race in dccp_rcv_close / sock_alloc_send_pskb

write to 0xffff888126a092aa of 1 bytes by interrupt on cpu 0:
 dccp_fin net/dccp/input.c:38 [inline]
 dccp_rcv_close+0x16e/0x1f0 net/dccp/input.c:77
 __dccp_rcv_established.isra.0+0x153/0x210 net/dccp/input.c:316
 dccp_rcv_established net/dccp/input.c:376 [inline]
 dccp_rcv_established+0x9c/0xc0 net/dccp/input.c:364
 dccp_v6_do_rcv+0x563/0x5f0 net/dccp/ipv6.c:606
 sk_backlog_rcv include/net/sock.h:945 [inline]
 __sk_receive_skb+0x1b1/0x500 net/core/sock.c:522
 dccp_v6_rcv+0x862/0xc60 net/dccp/ipv6.c:775
 ip6_protocol_deliver_rcu+0x22a/0xbe0 net/ipv6/ip6_input.c:409
 ip6_input_finish+0x30/0x50 net/ipv6/ip6_input.c:450
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip6_input+0x177/0x190 net/ipv6/ip6_input.c:459
 dst_input include/net/dst.h:442 [inline]
 ip6_rcv_finish+0x110/0x140 net/ipv6/ip6_input.c:76
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ipv6_rcv+0x1a1/0x1b0 net/ipv6/ip6_input.c:284
 __netif_receive_skb_one_core+0xa7/0xe0 net/core/dev.c:5010
 __netif_receive_skb+0x37/0xf0 net/core/dev.c:5124
 process_backlog+0x1d3/0x420 net/core/dev.c:5955

read to 0xffff888126a092aa of 1 bytes by task 13526 on cpu 1:
 sock_alloc_send_pskb+0xe9/0x510 net/core/sock.c:2225
 sock_alloc_send_skb+0x3b/0x50 net/core/sock.c:2257
 dccp_sendmsg+0x15c/0x780 net/dccp/proto.c:786
 inet_sendmsg+0x6d/0x90 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:637 [inline]
 sock_sendmsg+0x9f/0xc0 net/socket.c:657
 ___sys_sendmsg+0x2b7/0x5d0 net/socket.c:2311
 __sys_sendmmsg+0x123/0x350 net/socket.c:2413
 __do_sys_sendmmsg net/socket.c:2442 [inline]
 __se_sys_sendmmsg net/socket.c:2439 [inline]
 __x64_sys_sendmmsg+0x64/0x80 net/socket.c:2439
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 13526 Comm: syz-executor.2 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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