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From: Lai Jiangshan <laijs@linux.alibaba.com>
To: paulmck@kernel.org
Cc: linux-kernel@vger.kernel.org,
	Josh Triplett <josh@joshtriplett.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	rcu@vger.kernel.org
Subject: Re: [PATCH 04/11] rcu: cleanup rcu_preempt_deferred_qs()
Date: Fri, 1 Nov 2019 02:33:19 +0800	[thread overview]
Message-ID: <9791cdcb-591d-224a-bef0-05eba773e65b@linux.alibaba.com> (raw)
In-Reply-To: <20191031150719.GU20975@paulmck-ThinkPad-P72>



On 2019/10/31 11:07 下午, Paul E. McKenney wrote:
> On Thu, Oct 31, 2019 at 10:35:22PM +0800, Lai Jiangshan wrote:
>> On 2019/10/31 10:10 下午, Paul E. McKenney wrote:
>>> On Thu, Oct 31, 2019 at 10:07:59AM +0000, Lai Jiangshan wrote:
>>>> Don't need to set ->rcu_read_lock_nesting negative, irq-protected
>>>> rcu_preempt_deferred_qs_irqrestore() doesn't expect
>>>> ->rcu_read_lock_nesting to be negative to work, it even
>>>> doesn't access to ->rcu_read_lock_nesting any more.
>>>>
>>>> It is true that NMI over rcu_preempt_deferred_qs_irqrestore()
>>>> may access to ->rcu_read_lock_nesting, but it is still safe
>>>> since rcu_read_unlock_special() can protect itself from NMI.
>>>
>>> Hmmm...  Testing identified the need for this one.  But I will wait for
>>> your responses on the earlier patches before going any further through
>>> this series.
>>
>> Hmmm... I was wrong, it should be after patch7 to avoid
>> the scheduler deadlock.
> 
> I was wondering about that.  ;-)
> 

This patch was split from the core patch(patch8: don't use negative 
->rcu_read_lock_nesting).

When I reordered "fixing something" as patch1/2, I reordered
it close to the patch of clean up rcu_preempt_deferred_qs_irqrestore
caused this mistake.

I will reorder it back later and "fixing something" is fixing
nothing and I will drop patch 1/2. Could you continue to review
further through this series please? Sorry for any mistakes.

Thanks
Lai

> 							Thanx, Paul
> 
>>>> Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
>>>> ---
>>>>    kernel/rcu/tree_plugin.h | 5 -----
>>>>    1 file changed, 5 deletions(-)
>>>>
>>>> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
>>>> index 82595db04eec..9fe8138ed3c3 100644
>>>> --- a/kernel/rcu/tree_plugin.h
>>>> +++ b/kernel/rcu/tree_plugin.h
>>>> @@ -555,16 +555,11 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
>>>>    static void rcu_preempt_deferred_qs(struct task_struct *t)
>>>>    {
>>>>    	unsigned long flags;
>>>> -	bool couldrecurse = t->rcu_read_lock_nesting >= 0;
>>>>    	if (!rcu_preempt_need_deferred_qs(t))
>>>>    		return;
>>>> -	if (couldrecurse)
>>>> -		t->rcu_read_lock_nesting -= RCU_NEST_BIAS;
>>>>    	local_irq_save(flags);
>>>>    	rcu_preempt_deferred_qs_irqrestore(t, flags);
>>>> -	if (couldrecurse)
>>>> -		t->rcu_read_lock_nesting += RCU_NEST_BIAS;
>>>>    }
>>>>    /*
>>>> -- 
>>>> 2.20.1
>>>>

  reply	other threads:[~2019-10-31 18:33 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-31 10:07 [PATCH 00/11] rcu: introduce percpu rcu_preempt_depth Lai Jiangshan
2019-10-31 10:07 ` [PATCH 01/11] rcu: avoid leaking exp_deferred_qs into next GP Lai Jiangshan
2019-10-31 13:43   ` Paul E. McKenney
2019-10-31 18:19     ` Lai Jiangshan
2019-10-31 19:00       ` Paul E. McKenney
2019-10-31 10:07 ` [PATCH 02/11] rcu: fix bug when rcu_exp_handler() in nested interrupt Lai Jiangshan
2019-10-31 13:47   ` Paul E. McKenney
2019-10-31 14:20     ` Lai Jiangshan
2019-10-31 14:31     ` Paul E. McKenney
2019-10-31 15:14       ` Lai Jiangshan
2019-10-31 18:52         ` Paul E. McKenney
2019-11-01  0:19           ` Boqun Feng
2019-11-01  2:29             ` Lai Jiangshan
2019-10-31 10:07 ` [PATCH 03/11] rcu: clean up rcu_preempt_deferred_qs_irqrestore() Lai Jiangshan
2019-10-31 13:52   ` Paul E. McKenney
2019-10-31 15:25     ` Lai Jiangshan
2019-10-31 18:57       ` Paul E. McKenney
2019-10-31 19:02         ` Paul E. McKenney
2019-10-31 10:07 ` [PATCH 04/11] rcu: cleanup rcu_preempt_deferred_qs() Lai Jiangshan
2019-10-31 14:10   ` Paul E. McKenney
2019-10-31 14:35     ` Lai Jiangshan
2019-10-31 15:07       ` Paul E. McKenney
2019-10-31 18:33         ` Lai Jiangshan [this message]
2019-10-31 22:45           ` Paul E. McKenney
2019-10-31 10:08 ` [PATCH 05/11] rcu: clean all rcu_read_unlock_special after report qs Lai Jiangshan
2019-11-01 11:54   ` Paul E. McKenney
2019-10-31 10:08 ` [PATCH 06/11] rcu: clear t->rcu_read_unlock_special in one go Lai Jiangshan
2019-11-01 12:10   ` Paul E. McKenney
2019-11-01 16:58     ` Paul E. McKenney
2019-10-31 10:08 ` [PATCH 07/11] rcu: set special.b.deferred_qs before wake_up() Lai Jiangshan
2019-10-31 10:08 ` [PATCH 08/11] rcu: don't use negative ->rcu_read_lock_nesting Lai Jiangshan
2019-11-01 12:33   ` Paul E. McKenney
2019-11-16 13:04     ` Lai Jiangshan
2019-11-17 21:53       ` Paul E. McKenney
2019-11-18  1:54         ` Lai Jiangshan
2019-11-18 14:57           ` Paul E. McKenney
2019-10-31 10:08 ` [PATCH 09/11] rcu: wrap usages of rcu_read_lock_nesting Lai Jiangshan
2019-10-31 10:08 ` [PATCH 10/11] rcu: clear the special.b.need_qs in rcu_note_context_switch() Lai Jiangshan
2019-10-31 10:08 ` [PATCH 11/11] x86,rcu: use percpu rcu_preempt_depth Lai Jiangshan
2019-11-01 12:58   ` Paul E. McKenney
2019-11-01 13:13     ` Peter Zijlstra
2019-11-01 14:30       ` Paul E. McKenney
2019-11-01 15:32         ` Lai Jiangshan
2019-11-01 16:21           ` Paul E. McKenney
2019-11-01 15:47       ` Lai Jiangshan

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