netdev - Re: [PATCH net v3] ptp: prevent possible ABBA deadlock in ptp_clock

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Message-ID: <CAO9qdTFwFpQh8O-sQuLDXj2eH7L_yBGTk6jdinZVGg9ShQtssw@mail.gmail.com>
Date: Mon, 21 Jul 2025 20:36:17 +0900
From: Jeongjun Park <aha310510@...il.com>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: richardcochran@...il.com, andrew+netdev@...n.ch, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, yangbo.lu@....com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzbot+7cfb66a237c4a5fb22ad@...kaller.appspotmail.com
Subject: Re: [PATCH net v3] ptp: prevent possible ABBA deadlock in ptp_clock_freerun()

Vladimir Oltean <vladimir.oltean@....com> wrote:
>
> On Sat, Jul 19, 2025 at 09:40:22PM +0900, Jeongjun Park wrote:
> > diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c
> > index 7febfdcbde8b..b16c66c254ae 100644
> > --- a/drivers/ptp/ptp_vclock.c
> > +++ b/drivers/ptp/ptp_vclock.c
> > @@ -154,6 +154,20 @@ static long ptp_vclock_refresh(struct ptp_clock_info *ptp)
> >       return PTP_VCLOCK_REFRESH_INTERVAL;
> >  }
> >
> > +#ifdef CONFIG_LOCKDEP
> > +static void ptp_vclock_set_subclass(struct ptp_clock *ptp)
> > +{
> > +     lockdep_set_subclass(&ptp->n_vclocks_mux, PTP_LOCK_VIRTUAL);
> > +     lockdep_set_subclass(&ptp->clock.rwsem, PTP_LOCK_VIRTUAL);
> > +     lockdep_set_subclass(&ptp->tsevqs_lock, PTP_LOCK_VIRTUAL);
> > +     lockdep_set_subclass(&ptp->pincfg_mux, PTP_LOCK_VIRTUAL);
>
> Every other lock except &ptp->clock.rwsem is unrelated, and I wouldn't
> touch what is unrelated as part of a bug fix. That, plus I believe this
> breaks the data encapsulation of struct posix_clock. At least CC the
> "POSIX CLOCKS and TIMERS" maintainers in v4, so that they're aware of
> your intentions.

Okay, I'll CC the posix_clock maintainers.

However, I think ptp->n_vclocks_mux also needs to be annotating lock
subclass because there may be false positives due to recursive locking
between physical and virtual clocks.