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: Thu, 31 Oct 2019 22:35:22 +0800 [thread overview]
Message-ID: <1b5cf860-3d4a-954c-09ac-6383b38da4cf@linux.alibaba.com> (raw)
In-Reply-To: <20191031141056.GR20975@paulmck-ThinkPad-P72>
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.
>
> 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
>>
next prev parent reply other threads:[~2019-10-31 14:35 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 [this message]
2019-10-31 15:07 ` Paul E. McKenney
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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