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BUG: KCSAN: data-race in flush_signal_handlers / proc_pid_status

read to 0xffff88812aa9acc0 of 8 bytes by task 11496 on cpu 1:
 collect_sigign_sigcatch fs/proc/array.c:259 [inline]
 task_sig fs/proc/array.c:284 [inline]
 proc_pid_status+0xa0b/0x1000 fs/proc/array.c:421
 proc_single_show+0x92/0x120 fs/proc/base.c:756
 seq_read+0x350/0x9d0 fs/seq_file.c:229
 __vfs_read+0x67/0xc0 fs/read_write.c:425
 vfs_read fs/read_write.c:461 [inline]
 vfs_read+0x143/0x2c0 fs/read_write.c:446
 ksys_read+0xd5/0x1b0 fs/read_write.c:587
 __do_sys_read fs/read_write.c:597 [inline]
 __se_sys_read fs/read_write.c:595 [inline]
 __x64_sys_read+0x4c/0x60 fs/read_write.c:595
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812aa9acc0 of 8 bytes by task 11433 on cpu 0:
 flush_signal_handlers+0x6e/0xe0 kernel/signal.c:539
 setup_new_exec+0x325/0x3d0 fs/exec.c:1386
 load_elf_binary+0x738/0x2ef0 fs/binfmt_elf.c:859
 search_binary_handler fs/exec.c:1658 [inline]
 search_binary_handler+0x127/0x420 fs/exec.c:1635
 exec_binprm fs/exec.c:1701 [inline]
 __do_execve_file.isra.0+0xb6a/0x1140 fs/exec.c:1821
 do_execveat_common fs/exec.c:1867 [inline]
 do_execve fs/exec.c:1884 [inline]
 __do_sys_execve fs/exec.c:1960 [inline]
 __se_sys_execve fs/exec.c:1955 [inline]
 __x64_sys_execve+0x62/0x80 fs/exec.c:1955
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11433 Comm: ifdown Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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