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Subject: Re: WARNING in percpu_ref_exit (2)
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syzbot has bisected this bug to:

commit cbb537634780172137459dead490d668d437ef4d
Author: Jens Axboe <axboe@kernel.dk>
Date:   Mon Dec 9 18:22:50 2019 +0000

     io_uring: avoid ring quiesce for fixed file set unregister and update

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1118aac1e00000
start commit:   7ddd09fc Add linux-next specific files for 20191220
git tree:       linux-next
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1318aac1e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1518aac1e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f183b01c3088afc6
dashboard link: https://syzkaller.appspot.com/bug?extid=8c4a14856e657b43487c
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14b8f351e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14b51925e00000

Reported-by: syzbot+8c4a14856e657b43487c@syzkaller.appspotmail.com
Fixes: cbb537634780 ("io_uring: avoid ring quiesce for fixed file set  
unregister and update")

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