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Date: Wed, 17 Jan 2024 12:53:11 -0800
From: Boqun Feng <boqun.feng@gmail.com>
To: Zhiguo Niu <zhiguo.niu@unisoc.com>
Cc: 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
Subject: Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu
Message-ID: <Zag-N1369ATj400Q@boqun-archlinux>
References: <1705477714-10467-1-git-send-email-zhiguo.niu@unisoc.com>
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In-Reply-To: <1705477714-10467-1-git-send-email-zhiguo.niu@unisoc.com>

On Wed, Jan 17, 2024 at 03:48:34PM +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")
> Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
> Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

> ---
> changes of v2: update patch according to Boqun's suggestions.
> ---
> ---
>  kernel/locking/lockdep.c | 47 +++++++++++++++++++++++++++++++----------------
>  1 file changed, 31 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 151bd3d..ddcaa69 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -6184,25 +6184,27 @@ static struct pending_free *get_pending_free(void)
>  static void free_zapped_rcu(struct rcu_head *cb);
>  
>  /*
> - * Schedule an RCU callback if no RCU callback is pending. Must be called with
> - * the graph lock held.
> - */
> -static void call_rcu_zapped(struct pending_free *pf)
> +* See if we need to queue an RCU callback, must called with
> +* the lockdep lock held, returns false if either we don't have
> +* any pending free or the callback is already scheduled.
> +* Otherwise, a call_rcu() must follow this function call.
> +*/
> +static bool prepare_call_rcu_zapped(struct pending_free *pf)
>  {
>  	WARN_ON_ONCE(inside_selftest());
>  
>  	if (list_empty(&pf->zapped))
> -		return;
> +		return false;
>  
>  	if (delayed_free.scheduled)
> -		return;
> +		return false;
>  
>  	delayed_free.scheduled = true;
>  
>  	WARN_ON_ONCE(delayed_free.pf + delayed_free.index != pf);
>  	delayed_free.index ^= 1;
>  
> -	call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
> +	return true;
>  }
>  
>  /* The caller must hold the graph lock. May be called from RCU context. */
> @@ -6228,6 +6230,7 @@ static void free_zapped_rcu(struct rcu_head *ch)
>  {
>  	struct pending_free *pf;
>  	unsigned long flags;
> +	bool need_callback;
>  
>  	if (WARN_ON_ONCE(ch != &delayed_free.rcu_head))
>  		return;
> @@ -6239,14 +6242,17 @@ static void free_zapped_rcu(struct rcu_head *ch)
>  	pf = delayed_free.pf + (delayed_free.index ^ 1);
>  	__free_zapped_classes(pf);
>  	delayed_free.scheduled = false;
> +	need_callback =
> +		prepare_call_rcu_zapped(delayed_free.pf + delayed_free.index);
> +	lockdep_unlock();
> +	raw_local_irq_restore(flags);
>  
>  	/*
> -	 * If there's anything on the open list, close and start a new callback.
> -	 */
> -	call_rcu_zapped(delayed_free.pf + delayed_free.index);
> +	* If there's anything on the open list, close and start a new callback.
> +	*/
> +	if (need_callback)
> +		call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
>  
> -	lockdep_unlock();
> -	raw_local_irq_restore(flags);
>  }
>  
>  /*
> @@ -6286,6 +6292,7 @@ static void lockdep_free_key_range_reg(void *start, unsigned long size)
>  {
>  	struct pending_free *pf;
>  	unsigned long flags;
> +	bool need_callback;
>  
>  	init_data_structures_once();
>  
> @@ -6293,10 +6300,11 @@ static void lockdep_free_key_range_reg(void *start, unsigned long size)
>  	lockdep_lock();
>  	pf = get_pending_free();
>  	__lockdep_free_key_range(pf, start, size);
> -	call_rcu_zapped(pf);
> +	need_callback = prepare_call_rcu_zapped(pf);
>  	lockdep_unlock();
>  	raw_local_irq_restore(flags);
> -
> +	if (need_callback)
> +		call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
>  	/*
>  	 * Wait for any possible iterators from look_up_lock_class() to pass
>  	 * before continuing to free the memory they refer to.
> @@ -6390,6 +6398,7 @@ static void lockdep_reset_lock_reg(struct lockdep_map *lock)
>  	struct pending_free *pf;
>  	unsigned long flags;
>  	int locked;
> +	bool need_callback = false;
>  
>  	raw_local_irq_save(flags);
>  	locked = graph_lock();
> @@ -6398,11 +6407,13 @@ static void lockdep_reset_lock_reg(struct lockdep_map *lock)
>  
>  	pf = get_pending_free();
>  	__lockdep_reset_lock(pf, lock);
> -	call_rcu_zapped(pf);
> +	need_callback = prepare_call_rcu_zapped(pf);
>  
>  	graph_unlock();
>  out_irq:
>  	raw_local_irq_restore(flags);
> +	if (need_callback)
> +		call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
>  }
>  
>  /*
> @@ -6446,6 +6457,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
>  	struct pending_free *pf;
>  	unsigned long flags;
>  	bool found = false;
> +	bool need_callback = false;
>  
>  	might_sleep();
>  
> @@ -6466,11 +6478,14 @@ void lockdep_unregister_key(struct lock_class_key *key)
>  	if (found) {
>  		pf = get_pending_free();
>  		__lockdep_free_key_range(pf, key, 1);
> -		call_rcu_zapped(pf);
> +		need_callback = prepare_call_rcu_zapped(pf);
>  	}
>  	lockdep_unlock();
>  	raw_local_irq_restore(flags);
>  
> +	if (need_callback)
> +		call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
> +
>  	/* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
>  	synchronize_rcu();
>  }
> -- 
> 1.9.1
>