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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Wed, 7 Aug 2019 15:53:50 +0200
Message-ID: <CAAeHK+zLrYaE+Kt6AULPjKhBNknxPBWncfkTDmm3eFoLSpsffw@mail.gmail.com>
Subject: Re: possible deadlock in open_rio
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     syzbot <syzbot+7bbcbe9c9ff0cd49592a@syzkaller.appspotmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        Cesar Miquel <miquel@df.uba.ar>,
        rio500-users@lists.sourceforge.net,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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On Tue, Aug 6, 2019 at 9:13 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Thu, 1 Aug 2019, syzbot wrote:
>
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit:    7f7867ff usb-fuzzer: main usb gadget fuzzer driver
> > git tree:       https://github.com/google/kasan.git usb-fuzzer
> > console output: https://syzkaller.appspot.com/x/log.txt?x=136b6aec600000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=792eb47789f57810
> > dashboard link: https://syzkaller.appspot.com/bug?extid=7bbcbe9c9ff0cd49592a
> > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> >
> > Unfortunately, I don't have any reproducer for this crash yet.
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+7bbcbe9c9ff0cd49592a@syzkaller.appspotmail.com
> >
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > 5.3.0-rc2+ #23 Not tainted
> > ------------------------------------------------------
>
> Andrey:
>
> This should be completely reproducible, since it's a simple ABBA
> locking violation.  Maybe just introducing a time delay (to avoid races
> and give the open() call time to run) between the gadget creation and
> gadget removal would be enough to do it.

I've tried some simple approaches to reproducing this, but failed.
Should this require two rio500 devices to trigger?

>
> Is there any way you can test this?

Not yet.

>
> Alan Stern
>