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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Lai Jiangshan <laijs@linux.alibaba.com>
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: Thu, 31 Oct 2019 08:07:19 -0700	[thread overview]
Message-ID: <20191031150719.GU20975@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <1b5cf860-3d4a-954c-09ac-6383b38da4cf@linux.alibaba.com>

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.  ;-)

							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 15:07 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 [this message]
2019-10-31 18:33         ` Lai Jiangshan
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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