From: Lai Jiangshan <firstname.lastname@example.org>
To: Boqun Feng <email@example.com>,
"Paul E. McKenney" <firstname.lastname@example.org>
Josh Triplett <email@example.com>,
Steven Rostedt <firstname.lastname@example.org>,
Mathieu Desnoyers <email@example.com>,
Lai Jiangshan <firstname.lastname@example.org>,
Joel Fernandes <email@example.com>,
Subject: Re: [PATCH 02/11] rcu: fix bug when rcu_exp_handler() in nested interrupt
Date: Fri, 1 Nov 2019 10:29:41 +0800 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
On 2019/11/1 8:19 上午, Boqun Feng wrote:
> On Thu, Oct 31, 2019 at 11:52:58AM -0700, Paul E. McKenney wrote:
>> On Thu, Oct 31, 2019 at 11:14:23PM +0800, Lai Jiangshan wrote:
>>> On 2019/10/31 10:31 下午, Paul E. McKenney wrote:
>>>> On Thu, Oct 31, 2019 at 06:47:31AM -0700, Paul E. McKenney wrote:
>>>>> On Thu, Oct 31, 2019 at 10:07:57AM +0000, Lai Jiangshan wrote:
>>>>>> These is a possible bug (although which I can't triger yet)
>>>>>> since 2015 8203d6d0ee78
>>>>>> (rcu: Use single-stage IPI algorithm for RCU expedited grace period)
>>>>>> ->rcu_read_lock_nesting = -RCU_NEST_BIAS;
>>>>>> interrupt(); // before or after rcu_read_unlock_special()
>>>>>> fetch some rcu protected pointers
>>>>>> // exp GP starts in other cpu.
>>>>>> some works
>>>>>> NESTED interrupt for rcu_exp_handler();
>>>> Also, which platforms support nested interrupts? Last I knew, this was
>>>>>> report exp qs! BUG!
>>>>> Why would a quiescent state for the expedited grace period be reported
>>>>> here? This CPU is still in an RCU read-side critical section, isn't it?
>>>> And I now see what you were getting at here. Yes, the current code
>>>> assumes that interrupt-disabled regions, like hardware interrupt
>>>> handlers, cannot be interrupted. But if interrupt-disabled regions such
>>>> as hardware interrupt handlers can be interrupted (as opposed to being
>>>> NMIed), wouldn't that break a whole lot of stuff all over the place in
>>>> the kernel? So that sounds like an arch bug to me.
>>> I don't know when I started always assuming hardware interrupt
>>> handler can be nested by (other) interrupt. I can't find any
>>> documents say Linux don't allow nested interrupt handler.
>>> Google search suggests the opposite.
> FWIW, there is a LWN article talking about we disallow interrupt nesting
> in *most* cases:
Much thanks for the information!
> , that's unless a interrupt handler explicitly calls
> local_irq_enable_in_hardirq(), it remains irq disabled, which means no
> nesting interrupt allowed.
Even so the problem here will be fixed by patch7/8.
>> The results I am seeing look to be talking about threaded interrupt
>> handlers, which indeed can be interrupted by hardware interrupts. As can
>> softirq handlers. But these are not examples of a hardware interrupt
>> handler being interrupted by another hardware interrupt. For that to
>> work reasonably, something like a system priority level is required,
>> as in the old DYNIX/ptx kernel, or, going even farther back, DEC's RT-11.
>>> grep -rIni nested Documentation/memory-barriers.txt Documentation/x86/
>>> It still have some words about nested interrupt handler.
>> Some hardware does not differentiate between interrupts and exceptions,
>> for example, an illegal-instruction trap within an interrupt handler
>> might look in some ways like a nested interrupt.
>>> The whole patchset doesn't depend on this patch, and actually
>>> it is reverted later in the patchset. Dropping this patch
>>> can be an option for next round.
>> Sounds like a plan!
>> Thanx, Paul
next prev parent reply other threads:[~2019-11-01 2:29 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 [this message]
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
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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