netdev - Re: [syzbot] [net?] WARNING: bad unlock balance in do

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Message-ID: <CANn89iK=SrbwSN20nKY5y71huhsabLEdX=OGsdqwMPZOmNW8Gw@mail.gmail.com>
Date: Tue, 8 Apr 2025 13:33:17 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Aleksandr Nogikh <nogikh@...gle.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, stfomichev@...il.com, 
	andrew@...n.ch, davem@...emloft.net, horms@...nel.org, kuba@...nel.org, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, pabeni@...hat.com, 
	sdf@...ichev.me, syzbot+45016fe295243a7882d3@...kaller.appspotmail.com, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] WARNING: bad unlock balance in do_setlink

On Tue, Apr 8, 2025 at 12:44 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Tue, 8 Apr 2025 at 10:11, Aleksandr Nogikh <nogikh@...gle.com> wrote:
> >
> > On Mon, Apr 7, 2025 at 6:13 PM 'Kuniyuki Iwashima' via syzkaller-bugs
> > <syzkaller-bugs@...glegroups.com> wrote:
> > >
> > > From: Stanislav Fomichev <stfomichev@...il.com>
> > > Date: Mon, 7 Apr 2025 07:19:54 -0700
> > > > On 04/07, syzbot wrote:
> > > > > Hello,
> > > > >
> > > > > syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> > > > > unregister_netdevice: waiting for DEV to become free
> > > > >
> > > > > unregister_netdevice: waiting for batadv0 to become free. Usage count = 3
> > > >
> > > > So it does fix the lock unbalance issue, but now there is a hang?
> > >
> > > I think this is an orthogonal issue.
> > >
> > > I saw this in another report as well.
> > > https://lore.kernel.org/netdev/67f208ea.050a0220.0a13.025b.GAE@google.com/
> > >
> > > syzbot may want to find a better way to filter this kind of noise.
> > >
> >
> > Syzbot treats this message as a problem worthy of reporting since a
> > long time (Cc'd Dmitry who may remember the context):
> > https://github.com/google/syzkaller/commit/7a67784ca8bdc3b26cce2f0ec9a40d2dd9ec9396
> >
> > Since v6.15-rc1, we do observe it happen at least 10x more often than
> > before, both during fuzzing and while processing #syz test commands:
> > https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
>
> IIUC this error means a leaked reference count on a device, and the
> device and everything it references leaked forever + a kernel thread
> looping forever. This does not look like noise.
>
> Eric, should know more. Eric fixed a bunch of these bugs and added a
> ref count tracker to devices to provide better diagnostics. For some
> reason I don't see the reftracker output in the console output, but
> CONFIG_NET_DEV_REFCNT_TRACKER=y is enabled in the config.

I think that Kuniyuki patch was fixing the original syzbot report.

After fixing this trivial bug, another bug showed up,
and this second bug triggered "syzbot may want to find a better way to
filter this kind of noise." comment.


-ETOOMANYBUGS.