linux-kernel - Re: possible deadlock in xfrm_policy

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Date:   Thu, 24 Sep 2020 09:30:03 +0200
From:   peterz@...radead.org
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        syzbot <syzbot+c32502fd255cb3a44048@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: possible deadlock in xfrm_policy_delete

On Thu, Sep 24, 2020 at 06:44:12AM +0200, Dmitry Vyukov wrote:
> On Thu, Sep 24, 2020 at 6:36 AM Herbert Xu <herbert@...dor.apana.org.au> wrote:
> > >  (k-slock-AF_INET6){+.-.}-{2:2}

That's a seqlock.

> > What's going on with all these bogus lockdep reports?
> >
> > These are two completely different locks, one is for TCP and the
> > other is for SCTP.  Why is lockdep suddenly beoming confused about
> > this?
> >
> > FWIW this flood of bogus reports started on 16/Sep.
> 
> 
> FWIW one of the dups of this issue was bisected to:
> 
> commit 1909760f5fc3f123e47b4e24e0ccdc0fc8f3f106
> Author: Ahmed S. Darwish <a.darwish@...utronix.de>
> Date:   Fri Sep 4 15:32:31 2020 +0000
> 
>     seqlock: PREEMPT_RT: Do not starve seqlock_t writers
> 
> Can it be related?

Did that tree you're testing include 267580db047e ("seqlock: Unbreak
lockdep") ?