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Date: Fri, 2 Feb 2024 19:55:48 +0000
From: Carlos Llamas <cmllamas@google.com>
To: Zhiguo Niu <zhiguo.niu@unisoc.com>
Cc: bvanassche@acm.org, peterz@infradead.org, mingo@redhat.com,
	will@kernel.org, longman@redhat.com, boqun.feng@gmail.com,
	linux-kernel@vger.kernel.org, niuzhiguo84@gmail.com,
	ke.wang@unisoc.com, hongyu.jin@unisoc.com, stable@vger.kernel.org
Subject: Re: [PATCH V3] lockdep: fix deadlock issue between lockdep and rcu
Message-ID: <Zb1IxNd54z2Ib1N3@google.com>
References: <1706861676-26574-1-git-send-email-zhiguo.niu@unisoc.com>
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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 = 0xFFFFFF817F2A8A80, val = ?)
> -001|queued_spin_lock(inline) // try to hold nocb_gp_lock
> -001|do_raw_spin_lock(lock = 0xFFFFFF817F2A8A80)
> -002|__raw_spin_lock_irqsave(inline)
> -002|_raw_spin_lock_irqsave(lock = 0xFFFFFF817F2A8A80)
> -003|wake_nocb_gp_defer(inline)
> -003|__call_rcu_nocb_wake(rdp = 0xFFFFFF817F30B680)
> -004|__call_rcu_common(inline)
> -004|call_rcu(head = 0xFFFFFFC082EECC28, func = ?)
> -005|call_rcu_zapped(inline)
> -005|free_zapped_rcu(ch = ?)// hold graph lock
> -006|rcu_do_batch(rdp = 0xFFFFFF817F245680)
> -007|nocb_cb_wait(inline)
> -007|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F245680)
> -008|kthread(_create = 0xFFFFFF80803122C0)
> -009|ret_from_fork(asm)
> 
>      rcuop/y
> -000|queued_spin_lock_slowpath(lock = 0xFFFFFFC08291BBC8, val = 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 = 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 = 0xFFFFFF817F2A8680)
> -007|__call_rcu_common(inline)
> -007|call_rcu(head = 0xFFFFFFC0822E0B58, func = ?)
> -008|call_rcu_hurry(inline)
> -008|rcu_sync_call(inline)
> -008|rcu_sync_func(rhp = 0xFFFFFFC0822E0B58)
> -009|rcu_do_batch(rdp = 0xFFFFFF817F266680)
> -010|nocb_cb_wait(inline)
> -010|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F266680)
> -011|kthread(_create = 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>

Thanks