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BUG: KCSAN: data-race in sctp_poll / sctp_wfree

read to 0xffff8880b33ff9c8 of 4 bytes by task 26078 on cpu 1:
 sctp_writeable net/sctp/socket.c:9130 [inline]
 sctp_poll+0x220/0x500 net/sctp/socket.c:8496
 sock_poll+0xed/0x250 net/socket.c:1256
 vfs_poll include/linux/poll.h:90 [inline]
 do_pollfd fs/select.c:859 [inline]
 do_poll fs/select.c:907 [inline]
 do_sys_poll+0x4ac/0x990 fs/select.c:1001
 __do_sys_poll fs/select.c:1059 [inline]
 __se_sys_poll fs/select.c:1047 [inline]
 __x64_sys_poll+0x10f/0x250 fs/select.c:1047
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880b33ff9c8 of 4 bytes by interrupt on cpu 0:
 sctp_wfree+0x15c/0x4e0 net/sctp/socket.c:8973
 skb_release_head_state+0xb8/0x180 net/core/skbuff.c:652
 skb_release_all+0x1f/0x60 net/core/skbuff.c:663
 __kfree_skb net/core/skbuff.c:679 [inline]
 consume_skb net/core/skbuff.c:838 [inline]
 consume_skb+0x92/0x1c0 net/core/skbuff.c:832
 sctp_chunk_destroy net/sctp/sm_make_chunk.c:1454 [inline]
 sctp_chunk_put+0x10b/0x1a0 net/sctp/sm_make_chunk.c:1481
 sctp_chunk_free+0x4d/0x60 net/sctp/sm_make_chunk.c:1468
 sctp_outq_sack+0x657/0xc20 net/sctp/outqueue.c:1345
 sctp_cmd_process_sack net/sctp/sm_sideeffect.c:795 [inline]
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1353 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1184 [inline]
 sctp_do_sm+0x222e/0x2ef0 net/sctp/sm_sideeffect.c:1155
 sctp_assoc_bh_rcv+0x291/0x3e0 net/sctp/associola.c:1048
 sctp_inq_push+0x107/0x1a0 net/sctp/inqueue.c:80
 sctp_rcv+0x9eb/0x1da0 net/sctp/input.c:256
 sctp6_rcv+0x20/0x40 net/sctp/ipv6.c:1049
 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:4929
 __netif_receive_skb+0x37/0xf0 net/core/dev.c:5043
 process_backlog+0x207/0x4b0 net/core/dev.c:5874
 napi_poll net/core/dev.c:6311 [inline]
 net_rx_action+0x3ae/0xa90 net/core/dev.c:6379
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 run_ksoftirqd+0x46/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x37d/0x4a0 kernel/smpboot.c:165
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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