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BUG: KCSAN: data-race in __alloc_fd / do_select

read to 0xffff888123829d80 of 8 bytes by task 19137 on cpu 1:
 max_select_fd fs/select.c:446 [inline]
 do_select+0x315/0x1020 fs/select.c:487
 core_sys_select+0x312/0x650 fs/select.c:677
 kern_select+0x106/0x170 fs/select.c:718
 __do_sys_select fs/select.c:725 [inline]
 __se_sys_select fs/select.c:722 [inline]
 __x64_sys_select+0x70/0x90 fs/select.c:722
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888123829d80 of 8 bytes by task 19103 on cpu 0:
 __set_bit include/asm-generic/bitops/instrumented-non-atomic.h:29 [inline]
 __set_open_fd fs/file.c:241 [inline]
 __alloc_fd+0x200/0x3b0 fs/file.c:519
 get_unused_fd_flags+0x8b/0xc0 fs/file.c:545
 do_sys_open+0x2ab/0x4f0 fs/open.c:1095
 __do_sys_openat fs/open.c:1124 [inline]
 __se_sys_openat fs/open.c:1118 [inline]
 __x64_sys_openat+0x62/0x80 fs/open.c:1118
 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: 19103 Comm: syz-executor.3 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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