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BUG: KCSAN: data-race in ptrace_check_attach / zap_other_threads

write to 0xffff888010279500 of 8 bytes by task 9683 on cpu 1:
 task_clear_jobctl_pending kernel/signal.c:344 [inline]
 zap_other_threads+0x98/0x1e0 kernel/signal.c:1356
 do_group_exit+0x149/0x180 kernel/exit.c:917
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888010279500 of 8 bytes by task 9685 on cpu 0:
 ptrace_freeze_traced kernel/ptrace.c:178 [inline]
 ptrace_check_attach+0xdc/0x230 kernel/ptrace.c:247
 __do_sys_ptrace kernel/ptrace.c:1266 [inline]
 __se_sys_ptrace+0xdb/0x2e0 kernel/ptrace.c:1236
 __x64_sys_ptrace+0x51/0x60 kernel/ptrace.c:1236
 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: 9685 Comm: syz-executor.0 Not tainted 5.11.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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