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BUG: KCSAN: data-race in prepare_signal / ptrace_attach

write to 0xffff888137f763f0 of 4 bytes by task 25370 on cpu 0:
 ptrace_attach+0x203/0x4a0 kernel/ptrace.c:422
 __do_sys_ptrace kernel/ptrace.c:1295 [inline]
 __se_sys_ptrace+0xc1/0x2d0 kernel/ptrace.c:1275
 __x64_sys_ptrace+0x51/0x60 kernel/ptrace.c:1275
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888137f763f0 of 4 bytes by task 25383 on cpu 1:
 sig_ignored kernel/signal.c:116 [inline]
 prepare_signal+0x5a1/0x7b0 kernel/signal.c:965
 __send_signal+0x64/0x790 kernel/signal.c:1085
 send_signal+0x28b/0x3a0 kernel/signal.c:1248
 do_send_sig_info+0x9b/0xe0 kernel/signal.c:1297
 do_send_specific kernel/signal.c:3915 [inline]
 do_tkill kernel/signal.c:3941 [inline]
 __do_sys_tkill kernel/signal.c:3976 [inline]
 __se_sys_tkill+0x12b/0x180 kernel/signal.c:3970
 __x64_sys_tkill+0x2d/0x40 kernel/signal.c:3970
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0x00010001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 25383 Comm: syz-executor.2 Not tainted 5.17.0-rc5-syzkaller-00306-g2293be58d6a1-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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