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BUG: KCSAN: data-race in do_splice / fasync_insert_entry

write to 0xffff88812ad8bb40 of 4 bytes by task 12626 on cpu 1:
 fasync_insert_entry+0x137/0x160 fs/fcntl.c:939
 fasync_add_entry fs/fcntl.c:966 [inline]
 fasync_helper+0x59/0xc0 fs/fcntl.c:984
 pipe_fasync+0xdd/0x160 fs/pipe.c:751
 setfl fs/fcntl.c:73 [inline]
 do_fcntl+0xb2b/0xbc0 fs/fcntl.c:347
 __do_sys_fcntl fs/fcntl.c:463 [inline]
 __se_sys_fcntl+0xc2/0x180 fs/fcntl.c:448
 __x64_sys_fcntl+0x3f/0x50 fs/fcntl.c:448
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812ad8bb40 of 4 bytes by task 12640 on cpu 0:
 do_splice+0xc8a/0x10c0 fs/splice.c:1167
 __do_sys_splice fs/splice.c:1419 [inline]
 __se_sys_splice fs/splice.c:1401 [inline]
 __x64_sys_splice+0xf2/0x190 fs/splice.c:1401
 do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12640 Comm: syz-executor.0 Not tainted 5.8.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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