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BUG: KCSAN: data-race in complete_signal / task_stopped_code

write to 0xffff8880812c95f4 of 4 bytes by task 15191 on cpu 1:
 complete_signal+0x50b/0x5c0 kernel/signal.c:1044
 __send_signal+0x675/0x8a0 kernel/signal.c:1180
 send_signal+0x211/0x2a0 kernel/signal.c:1241
 do_send_sig_info+0x59/0xc0 kernel/signal.c:1290
 do_send_specific+0xd8/0x100 kernel/signal.c:3780
 do_tkill+0xf8/0x130 kernel/signal.c:3806
 __do_sys_tkill kernel/signal.c:3841 [inline]
 __se_sys_tkill kernel/signal.c:3835 [inline]
 __x64_sys_tkill+0x4d/0x70 kernel/signal.c:3835
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880812c95f4 of 4 bytes by task 15196 on cpu 0:
 task_stopped_code+0xa9/0xe0 kernel/exit.c:1103
 wait_task_stopped kernel/exit.c:1141 [inline]
 wait_consider_task+0x5bd/0x1c60 kernel/exit.c:1342
 do_wait_thread kernel/exit.c:1368 [inline]
 do_wait+0x1c7/0x4c0 kernel/exit.c:1439
 kernel_wait4+0x146/0x230 kernel/exit.c:1611
 __do_sys_wait4+0xea/0x100 kernel/exit.c:1623
 __se_sys_wait4 kernel/exit.c:1619 [inline]
 __x64_sys_wait4+0x59/0x70 kernel/exit.c:1619
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15196 Comm: syz-executor.0 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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