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BUG: KCSAN: data-race in pfkey_broadcast / pfkey_promisc

write to 0xffff888012c176fc of 4 bytes by task 16013 on cpu 1:
 pfkey_promisc+0x5d/0x180 net/key/af_key.c:1894
 pfkey_process net/key/af_key.c:2841 [inline]
 pfkey_sendmsg+0x6aa/0x8c0 net/key/af_key.c:3680
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg net/socket.c:674 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2350
 ___sys_sendmsg net/socket.c:2404 [inline]
 __sys_sendmsg+0x1ed/0x270 net/socket.c:2433
 __do_sys_sendmsg net/socket.c:2442 [inline]
 __se_sys_sendmsg net/socket.c:2440 [inline]
 __x64_sys_sendmsg+0x42/0x50 net/socket.c:2440
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888012c176fc of 4 bytes by task 16009 on cpu 0:
 pfkey_broadcast+0xec/0x280 net/key/af_key.c:242
 pfkey_error net/key/af_key.c:344 [inline]
 pfkey_sendmsg+0x885/0x8c0 net/key/af_key.c:3684
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg net/socket.c:674 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2350
 ___sys_sendmsg net/socket.c:2404 [inline]
 __sys_sendmsg+0x1ed/0x270 net/socket.c:2433
 __do_sys_sendmsg net/socket.c:2442 [inline]
 __se_sys_sendmsg net/socket.c:2440 [inline]
 __x64_sys_sendmsg+0x42/0x50 net/socket.c:2440
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16009 Comm: syz-executor.0 Not tainted 5.12.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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