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BUG: KCSAN: data-race in coredump_wait / ptrace_stop

write to 0xffff88813dd69648 of 8 bytes by task 21245 on cpu 1:
 zap_threads fs/coredump.c:381 [inline]
 coredump_wait+0x595/0x900 fs/coredump.c:462
 do_coredump+0x1b8/0x1830 fs/coredump.c:628
 get_signal+0xf36/0x15e0 kernel/signal.c:2794
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:865
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x49/0x90 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813dd69648 of 8 bytes by task 21244 on cpu 0:
 may_ptrace_stop kernel/signal.c:2118 [inline]
 ptrace_stop+0x2bb/0x670 kernel/signal.c:2216
 ptrace_do_notify kernel/signal.c:2294 [inline]
 ptrace_notify+0x107/0x180 kernel/signal.c:2304
 ptrace_report_syscall include/linux/tracehook.h:66 [inline]
 tracehook_report_syscall_exit include/linux/tracehook.h:130 [inline]
 arch_syscall_exit_tracehook include/linux/entry-common.h:297 [inline]
 syscall_exit_work+0xdc/0x1d0 kernel/entry/common.c:257
 syscall_exit_to_user_mode_prepare kernel/entry/common.c:284 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
 syscall_exit_to_user_mode+0x33/0x40 kernel/entry/common.c:302
 do_syscall_64+0x49/0x90 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000000 -> 0xffffc9000f67bc60

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 21244 Comm: syz-executor.0 Not tainted 5.14.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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