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From: Boqun Feng <boqun.feng@gmail.com>
Date: Thu, 1 Feb 2024 11:48:29 -0800
Message-ID: <CAL0jBu-2jrhBzTo+ZneFMpsTsqUMLVQCYCAQKqd6BHjv3-kxhQ@mail.gmail.com>
Subject: Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu
To: Bart Van Assche <bvanassche@acm.org>
Cc: Zhiguo Niu <zhiguo.niu@unisoc.com>, peterz@infradead.org, mingo@redhat.com, 
	will@kernel.org, longman@redhat.com, linux-kernel@vger.kernel.org, 
	niuzhiguo84@gmail.com, ke.wang@unisoc.com, xuewen.yan@unisoc.com, 
	Carlos Llamas <cmllamas@google.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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On Thu, Feb 1, 2024 at 11:28=E2=80=AFAM Bart Van Assche <bvanassche@acm.org=
> wrote:
>
> On 1/16/24 23:48, Zhiguo Niu wrote:
> > -000|queued_spin_lock_slowpath(lock =3D 0xFFFFFFC08291BBC8, val =3D 0)
> > -001|queued_spin_lock()
> > -001|lockdep_lock()
> > -001|graph_lock() // try to hold graph lock
> > -002|lookup_chain_cache_add()
> > -002|validate_chain()
> > -003|lock_acquire
> > -004|_raw_spin_lock_irqsave(lock =3D 0xFFFFFF817F211D80)
> > -005|lock_timer_base(inline)
> > -006|mod_timer(inline)
> > -006|wake_nocb_gp_defer(inline)// hold nocb_gp_lock
> > -006|__call_rcu_nocb_wake(rdp =3D 0xFFFFFF817F2A8680)
> > -007|__call_rcu_common(inline)
> > -007|call_rcu(head =3D 0xFFFFFFC0822E0B58, func =3D ?)
> > -008|call_rcu_hurry(inline)
> > -008|rcu_sync_call(inline)
> > -008|rcu_sync_func(rhp =3D 0xFFFFFFC0822E0B58)
> > -009|rcu_do_batch(rdp =3D 0xFFFFFF817F266680)
> > -010|nocb_cb_wait(inline)
> > -010|rcu_nocb_cb_kthread(arg =3D 0xFFFFFF817F266680)
> > -011|kthread(_create =3D 0xFFFFFF8080363740)
> > -012|ret_from_fork(asm)
>
> The above call trace shows a graph_lock() call from inside lock_timer_bas=
e().
> How can that happen? In lock_timer_base() I see a raw_spin_lock_irqsave()=
 call.
> Did I perhaps overlook something?
>

(replying from gmail web, please forgive the format)

raw_spin_lock_irqsave():
  lock_acquire():
    __lock_acquire():
      validate_chain():
        lookup_chain_cache_add():
          graph_lock();

Basically, every lock acquisition may lock the lockdep graph because
of dependency checking.

Regards,
Boqun


> Thanks,
>
> Bart.
>