syzbot suspects this issue was fixed by commit:

commit a890d01e4ee016978776e45340e521b3bbbdf41f
Author: Hao Xu [off-list ref]
Date:   Wed Jul 28 03:03:22 2021 +0000

    io_uring: fix poll requests leaking second poll entries

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15d8819d300000
start commit:   98f7fdced2e0 Merge tag 'irq-urgent-2021-07-11' of git://gi..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=139b08f9b7481d26
dashboard link: https://syzkaller.appspot.com/bug?extid=f2aca089e6f77e5acd46
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11650180300000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1510c6b0300000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: io_uring: fix poll requests leaking second poll entries

For information about bisection process see: https://goo.gl/tpsmEJ#bisection