linux-kernel - Re: possible deadlock in open

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Message-ID: <1565185044.15973.0.camel@suse.com>
Date:   Wed, 07 Aug 2019 15:37:24 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        syzbot <syzbot+7bbcbe9c9ff0cd49592a@...kaller.appspotmail.com>
Cc:     miquel@...uba.ar, andreyknvl@...gle.com,
        syzkaller-bugs@...glegroups.com, gregkh@...uxfoundation.org,
        rio500-users@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: possible deadlock in open_rio

Am Dienstag, den 06.08.2019, 15:13 -0400 schrieb Alan Stern:
> 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.

Hi,

technically yes. However in practical terms the straight revert I sent
out yesterday should fix it.

	Regards
		Oliver