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BUG: KCSAN: data-race in flush_signal_handlers / proc_pid_status

read to 0xffff8880a24b48e0 of 8 bytes by task 7794 on cpu 0:
 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+0x89/0xe0 fs/proc/base.c:756
 seq_read+0x350/0x960 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/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880a24b48e0 of 8 bytes by task 7780 on cpu 1:
 flush_signal_handlers+0x6e/0xe0 kernel/signal.c:539
 setup_new_exec+0x325/0x3d0 fs/exec.c:1387
 load_elf_binary+0x78a/0x2ec0 fs/binfmt_elf.c:860
 search_binary_handler fs/exec.c:1659 [inline]
 search_binary_handler+0x127/0x420 fs/exec.c:1636
 exec_binprm fs/exec.c:1702 [inline]
 __do_execve_file.isra.0+0xb76/0x11d0 fs/exec.c:1822
 do_execveat_common fs/exec.c:1868 [inline]
 do_execve fs/exec.c:1885 [inline]
 __do_sys_execve fs/exec.c:1961 [inline]
 __se_sys_execve fs/exec.c:1956 [inline]
 __x64_sys_execve+0x62/0x80 fs/exec.c:1956
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7780 Comm: ifup Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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