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BUG: KCSAN: data-race in __alloc_fd / do_select

write to 0xffff888122c97f80 of 8 bytes by task 8613 on cpu 0:
 instrument_write include/linux/instrumented.h:42 [inline]
 __set_bit include/asm-generic/bitops/instrumented-non-atomic.h:27 [inline]
 __set_open_fd fs/file.c:241 [inline]
 __alloc_fd+0x207/0x3b0 fs/file.c:519
 __get_unused_fd_flags fs/file.c:545 [inline]
 get_unused_fd_flags+0x85/0xb0 fs/file.c:550
 __do_pipe_flags fs/pipe.c:946 [inline]
 __do_pipe_flags+0x7e/0x170 fs/pipe.c:934
 do_pipe2+0x3c/0x150 fs/pipe.c:990
 __do_sys_pipe fs/pipe.c:1013 [inline]
 __se_sys_pipe fs/pipe.c:1011 [inline]
 __x64_sys_pipe+0x27/0x40 fs/pipe.c:1011
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888122c97f80 of 8 bytes by task 8615 on cpu 1:
 max_select_fd fs/select.c:446 [inline]
 do_select+0x315/0x1020 fs/select.c:487
 core_sys_select+0x2c7/0x5f0 fs/select.c:677
 do_pselect.constprop.0+0x125/0x160 fs/select.c:759
 __do_sys_pselect6 fs/select.c:784 [inline]
 __se_sys_pselect6 fs/select.c:769 [inline]
 __x64_sys_pselect6+0x12a/0x160 fs/select.c:769
 do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8615 Comm: syz-executor.2 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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