Re: WARNING in perf_group_attach

[syzbot]

syzbot has bisected this bug to:

commit 33ea4b24277b06dbc55d7f5772a46f029600255e
Author: Song Liu <songliubraving@xxxxxx>
Date:   Wed Dec 6 22:45:16 2017 +0000

    perf/core: Implement the 'perf_uprobe' PMU

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1038fecae00000
start commit:   0072a0c1 Merge tag 'media/v4.20-4' of git://git.kernel.org..
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1238fecae00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1438fecae00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b9cc5a440391cbfd
dashboard link: https://syzkaller.appspot.com/bug?extid=23fe48cbe532abffa52e
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=135e93eb400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13189415400000

Reported-by: syzbot+23fe48cbe532abffa52e@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")

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