linux-kernel - Re: possible deadlock in open

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Message-ID: <Pine.LNX.4.44L0.1908061509040.1571-100000@iolanthe.rowland.org>
Date:   Tue, 6 Aug 2019 15:13:41 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     syzbot <syzbot+7bbcbe9c9ff0cd49592a@...kaller.appspotmail.com>
cc:     andreyknvl@...gle.com, <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <miquel@...uba.ar>, <rio500-users@...ts.sourceforge.net>,
        <syzkaller-bugs@...glegroups.com>
Subject: Re: possible deadlock in open_rio

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@...kaller.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.

Is there any way you can test this?

Alan Stern