From: Dmitry Vyukov <dvyukov@google.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Taehee Yoo <ap420073@gmail.com>,
syzbot <syzbot+aaa6fa4949cc5d9b7b25@syzkaller.appspotmail.com>,
Ingo Molnar <mingo@kernel.org>, Will Deacon <will.deacon@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: BUG: MAX_LOCKDEP_CHAINS too low!
Date: Thu, 16 Jan 2020 06:25:46 +0100 [thread overview]
Message-ID: <CACT4Y+YuM55YUT37jwRP163J7ha25cN03sZ5WqTUPkz3e43Ggw@mail.gmail.com> (raw)
In-Reply-To: <CAM_iQpVtcNFeEtW15z_nZoyC1Q-_pCq+UfZ4vYBB3Lb2CMm4Mg@mail.gmail.com>
On Wed, Jan 15, 2020 at 10:53 PM Cong Wang <xiyou.wangcong@gmail.com> wrote:
> > +Taehee, Cong,
> >
> > In the other thread Taehee mentioned the creation of dynamic keys for
> > net devices that was added recently and that they are subject to some
> > limits.
> > syzkaller creates lots of net devices for isolation (several dozens
> > per test process, but then these can be created and destroyed
> > periodically). I wonder if it's the root cause of the lockdep limits
> > problems?
>
> Very possibly. In current code base, there are 4 lockdep keys
> per netdev:
>
> struct lock_class_key qdisc_tx_busylock_key;
> struct lock_class_key qdisc_running_key;
> struct lock_class_key qdisc_xmit_lock_key;
> struct lock_class_key addr_list_lock_key;
>
> so the number of lockdep keys is at least 4x number of network
> devices.
And these are not freed/reused, right? So with dynamic keys LOCKDEP
inherently can't handle prolonged running, only O(1) work?
> I think only addr_list_lock_key is necessary as it has a nested
> locking use case, all the rest are not. Taehee, do you agree?
>
> I plan to remove at least qdisc_xmit_lock_key for net-next
> after the fix for net gets merged.
next prev parent reply other threads:[~2020-01-16 5:25 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-28 5:51 BUG: MAX_LOCKDEP_CHAINS too low! syzbot
2018-09-28 6:06 ` Dmitry Vyukov
2018-09-28 7:00 ` Peter Zijlstra
2018-09-28 7:56 ` Dmitry Vyukov
2020-01-09 10:59 ` Dmitry Vyukov
2020-01-13 11:11 ` Dmitry Vyukov
2020-01-15 21:53 ` Cong Wang
2020-01-16 5:25 ` Dmitry Vyukov [this message]
2020-01-16 15:32 ` Taehee Yoo
2020-01-16 17:05 ` Dmitry Vyukov
2020-01-16 15:09 ` Taehee Yoo
2020-01-18 20:41 ` Cong Wang
2020-03-04 8:03 ` Dmitry Vyukov
2020-03-04 23:19 ` Cong Wang
2020-01-14 8:43 ` Peter Zijlstra
2020-01-14 10:18 ` Dmitry Vyukov
2019-10-20 23:33 ` syzbot
2020-04-15 18:52 ` Cong Wang
2020-04-15 19:17 ` syzbot
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