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 <Zb1IxNd54z2Ib1N3@google.com> <2024020233-wildland-blouse-2f2e@gregkh>
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From: Zhiguo Niu <niuzhiguo84@gmail.com>
Date: Tue, 6 Feb 2024 18:37:05 +0800
Message-ID: <CAHJ8P3L8A4uUwDuD5WQkDGdsOB6jWBdPFzR98mCiAh-0LtM91A@mail.gmail.com>
Subject: Re: [PATCH V3] lockdep: fix deadlock issue between lockdep and rcu
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Carlos Llamas <cmllamas@google.com>, Zhiguo Niu <zhiguo.niu@unisoc.com>, bvanassche@acm.org, 
	peterz@infradead.org, mingo@redhat.com, will@kernel.org, longman@redhat.com, 
	boqun.feng@gmail.com, linux-kernel@vger.kernel.org, ke.wang@unisoc.com, 
	hongyu.jin@unisoc.com, stable@vger.kernel.org
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hi Greg,

On Sat, Feb 3, 2024 at 5:36=E2=80=AFAM Greg KH <gregkh@linuxfoundation.org>=
 wrote:
>
> On Fri, Feb 02, 2024 at 07:55:48PM +0000, Carlos Llamas wrote:
> > On Fri, Feb 02, 2024 at 04:14:36PM +0800, Zhiguo Niu wrote:
> > > There is a deadlock scenario between lockdep and rcu when
> > > rcu nocb feature is enabled, just as following call stack:
> > >
> > >      rcuop/x
> > > -000|queued_spin_lock_slowpath(lock =3D 0xFFFFFF817F2A8A80, val =3D ?=
)
> > > -001|queued_spin_lock(inline) // try to hold nocb_gp_lock
> > > -001|do_raw_spin_lock(lock =3D 0xFFFFFF817F2A8A80)
> > > -002|__raw_spin_lock_irqsave(inline)
> > > -002|_raw_spin_lock_irqsave(lock =3D 0xFFFFFF817F2A8A80)
> > > -003|wake_nocb_gp_defer(inline)
> > > -003|__call_rcu_nocb_wake(rdp =3D 0xFFFFFF817F30B680)
> > > -004|__call_rcu_common(inline)
> > > -004|call_rcu(head =3D 0xFFFFFFC082EECC28, func =3D ?)
> > > -005|call_rcu_zapped(inline)
> > > -005|free_zapped_rcu(ch =3D ?)// hold graph lock
> > > -006|rcu_do_batch(rdp =3D 0xFFFFFF817F245680)
> > > -007|nocb_cb_wait(inline)
> > > -007|rcu_nocb_cb_kthread(arg =3D 0xFFFFFF817F245680)
> > > -008|kthread(_create =3D 0xFFFFFF80803122C0)
> > > -009|ret_from_fork(asm)
> > >
> > >      rcuop/y
> > > -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)
> > >
> > > rcuop/x and rcuop/y are rcu nocb threads with the same nocb gp thread=
.
> > > This patch release the graph lock before lockdep call_rcu.
> > >
> > > Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no =
longer in use")
> > > Cc: <stable@vger.kernel.org>
> > > Cc: Boqun Feng <boqun.feng@gmail.com>
> > > Cc: Waiman Long <longman@redhat.com>
> > > Cc: Carlos Llamas <cmllamas@google.com>
> > > Cc: Bart Van Assche <bvanassche@acm.org>
> > > Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
> > > Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
> > > ---
> > > changes of v3: correct code comments and add Cc tag.
> > > changes of v2: update patch according to Boqun's suggestions.
> > > ---
> >
> > It seems v3 should have collected the review tags from Boqun and Waiman=
.
> > Also, I'm actually Cc'ing stable here. I hope that is enough.
> > FWIW, this looks fine to me.
> >
> > Reviewed-by: Carlos Llamas <cmllamas@google.com>
>
>
> <formletter>
>
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.ht=
ml
> for how to do this properly.
>
> </formletter>

I see that many commits in mainline use Cc: <stable@vger.kernel.org>
directly without other information,
and I also find this information from above link: "Note, such tagging
is unnecessary if the stable team can
derive the appropriate versions from Fixes: tags."

In addition, this fixed commit "a0b0fd53e1e6 ("locking/lockdep: Free
lock classes that are no longer in use")"
was committed in 2019, so I am not very sure which start version
should be added to stabe tag.
Do you have any good suggestions?
thanks!