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BUG: KCSAN: data-race in complete_signal / futex_wait_queue_me

read to 0xffff8880b9592010 of 8 bytes by task 27916 on cpu 0:
 wants_signal kernel/signal.c:978 [inline]
 complete_signal+0xcd/0x5e0 kernel/signal.c:995
 __send_signal+0x5ea/0x870 kernel/signal.c:1175
 send_signal+0x224/0x2b0 kernel/signal.c:1236
 do_send_sig_info+0x5f/0xc0 kernel/signal.c:1285
 do_send_specific+0xe7/0x110 kernel/signal.c:3775
 do_tkill+0xf7/0x130 kernel/signal.c:3801
 __do_sys_tkill kernel/signal.c:3836 [inline]
 __se_sys_tkill kernel/signal.c:3830 [inline]
 __x64_sys_tkill+0x50/0x70 kernel/signal.c:3830
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880b9592010 of 8 bytes by task 27895 on cpu 1:
 futex_wait_queue_me+0x1f8/0x290 kernel/futex.c:2629
 futex_wait+0x19b/0x3f0 kernel/futex.c:2733
 do_futex+0xe9/0x18d0 kernel/futex.c:3644
 __do_sys_futex kernel/futex.c:3705 [inline]
 __se_sys_futex kernel/futex.c:3673 [inline]
 __x64_sys_futex+0x2cd/0x3f0 kernel/futex.c:3673
 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: 27895 Comm: syz-executor.1 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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