Date:	Thu, 08 Aug 2013 10:33:15 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	paulmck@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, C.Emde@...dl.org
Subject: Re: [PATCH 0/8] rcu: Ensure rcu read site is deadlock-immunity

On 08/08/2013 10:12 AM, Steven Rostedt wrote:
> On Thu, 2013-08-08 at 09:47 +0800, Lai Jiangshan wrote:
> 
>>> [  393.641012]        CPU0
>>> [  393.641012]        ----
>>> [  393.641012]   lock(&lock->wait_lock);
>>> [  393.641012]   <Interrupt>
>>> [  393.641012]     lock(&lock->wait_lock);
>>
>> Patch2 causes it!
>> When I found all lock which can (chained) nested in rcu_read_unlock_special(),
>> I didn't notice rtmutex's lock->wait_lock is not nested in irq-disabled.
>>
>> Two ways to fix it:
>> 1) change rtmutex's lock->wait_lock, make it alwasys irq-disabled.
>> 2) revert my patch2
> 
> Your patch 2 states:
> 
> "After patch 10f39bb1, "special & RCU_READ_UNLOCK_BLOCKED" can't be true
> in irq nor softirq.(due to RCU_READ_UNLOCK_BLOCKED can only be set
> when preemption)"

Patch5 adds "special & RCU_READ_UNLOCK_BLOCKED" back in irq nor softirq.
This new thing is handle in patch5 if I did not do wrong things in patch5.
(I don't notice rtmutex's lock->wait_lock is not irqs-disabled in patch5)

> 
> But then below we have:
> 
> 
>>
>>> [  393.641012] 
>>> [  393.641012]  *** DEADLOCK ***
>>> [  393.641012] 
>>> [  393.641012] no locks held by rcu_torture_rea/697.
>>> [  393.641012] 
>>> [  393.641012] stack backtrace:
>>> [  393.641012] CPU: 3 PID: 697 Comm: rcu_torture_rea Not tainted 3.11.0-rc1+ #1
>>> [  393.641012] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
>>> [  393.641012]  ffffffff8586fea0 ffff88001fcc3a78 ffffffff8187b4cb ffffffff8104a261
>>> [  393.641012]  ffff88001e1a20c0 ffff88001fcc3ad8 ffffffff818773e4 0000000000000000
>>> [  393.641012]  ffff880000000000 ffff880000000001 ffffffff81010a0a 0000000000000001
>>> [  393.641012] Call Trace:
>>> [  393.641012]  <IRQ>  [<ffffffff8187b4cb>] dump_stack+0x4f/0x84
>>> [  393.641012]  [<ffffffff8104a261>] ? console_unlock+0x291/0x410
>>> [  393.641012]  [<ffffffff818773e4>] print_usage_bug+0x1f5/0x206
>>> [  393.641012]  [<ffffffff81010a0a>] ? save_stack_trace+0x2a/0x50
>>> [  393.641012]  [<ffffffff810ae603>] mark_lock+0x283/0x2e0
>>> [  393.641012]  [<ffffffff810ada10>] ? print_irq_inversion_bug.part.40+0x1f0/0x1f0
>>> [  393.641012]  [<ffffffff810aef66>] __lock_acquire+0x906/0x1d40
>>> [  393.641012]  [<ffffffff810ae94b>] ? __lock_acquire+0x2eb/0x1d40
>>> [  393.641012]  [<ffffffff810ae94b>] ? __lock_acquire+0x2eb/0x1d40
>>> [  393.641012]  [<ffffffff810b0a65>] lock_acquire+0x95/0x210
>>> [  393.641012]  [<ffffffff818860f3>] ? rt_mutex_unlock+0x53/0x100
>>> [  393.641012]  [<ffffffff81886d26>] _raw_spin_lock+0x36/0x50
>>> [  393.641012]  [<ffffffff818860f3>] ? rt_mutex_unlock+0x53/0x100
>>> [  393.641012]  [<ffffffff818860f3>] rt_mutex_unlock+0x53/0x100
>>> [  393.641012]  [<ffffffff810ee3ca>] rcu_read_unlock_special+0x17a/0x2a0
>>> [  393.641012]  [<ffffffff810ee803>] rcu_check_callbacks+0x313/0x950
>>> [  393.641012]  [<ffffffff8107a6bd>] ? hrtimer_run_queues+0x1d/0x180
>>> [  393.641012]  [<ffffffff810abb9d>] ? trace_hardirqs_off+0xd/0x10
>>> [  393.641012]  [<ffffffff8105bae3>] update_process_times+0x43/0x80
>>> [  393.641012]  [<ffffffff810a9801>] tick_sched_handle.isra.10+0x31/0x40
>>> [  393.641012]  [<ffffffff810a98f7>] tick_sched_timer+0x47/0x70
>>> [  393.641012]  [<ffffffff8107941c>] __run_hrtimer+0x7c/0x490
>>> [  393.641012]  [<ffffffff810a260d>] ? ktime_get_update_offsets+0x4d/0xe0
>>> [  393.641012]  [<ffffffff810a98b0>] ? tick_nohz_handler+0xa0/0xa0
>>> [  393.641012]  [<ffffffff8107a017>] hrtimer_interrupt+0x107/0x260
> 
> The hrtimer_interrupt is calling a rt_mutex_unlock? How did that happen?
> Did it first call a rt_mutex_lock?
> 
> If patch two was the culprit, I'm thinking the idea behind patch two is
> wrong. The only option is to remove patch number two!

removing patch number two can solve the problem found be Paul, but it is not the best.
because I can't declare that rcu is deadlock-immunity
(it will be deadlock if rcu read site overlaps with rtmutex's lock->wait_lock
if I only remove patch2)
I must do more things, but I think it is still better than changing rtmutex's lock->wait_lock.

Thanks,
Lai

> 
> Or perhaps I missed something.
> 
> -- Steve
> 
> 
>>> [  393.641012]  [<ffffffff81030173>] local_apic_timer_interrupt+0x33/0x60
>>> [  393.641012]  [<ffffffff8103059e>] smp_apic_timer_interrupt+0x3e/0x60
>>> [  393.641012]  [<ffffffff8189022f>] apic_timer_interrupt+0x6f/0x80
>>> [  393.641012]  <EOI>  [<ffffffff810ee250>] ? rcu_scheduler_starting+0x60/0x60
>>> [  393.641012]  [<ffffffff81072101>] ? __rcu_read_unlock+0x91/0xa0
>>> [  393.641012]  [<ffffffff810e80e3>] rcu_torture_read_unlock+0x33/0x70
>>> [  393.641012]  [<ffffffff810e8f54>] rcu_torture_reader+0xe4/0x450
>>> [  393.641012]  [<ffffffff810e92c0>] ? rcu_torture_reader+0x450/0x450
>>> [  393.641012]  [<ffffffff810e8e70>] ? rcutorture_trace_dump+0x30/0x30
>>> [  393.641012]  [<ffffffff810759d6>] kthread+0xd6/0xe0
>>> [  393.641012]  [<ffffffff818874bb>] ? _raw_spin_unlock_irq+0x2b/0x60
>>> [  393.641012]  [<ffffffff81075900>] ? flush_kthread_worker+0x130/0x130
>>> [  393.641012]  [<ffffffff8188f52c>] ret_from_fork+0x7c/0xb0
>>> [  393.641012]  [<ffffffff81075900>] ? flush_kthread_worker+0x130/0x130
>>>
>>> I don't see this without your patches.
>>>
>>> .config attached.  The other configurations completed without errors.
>>> Short tests, 30 minutes per configuration.
>>>
>>> Thoughts?
>>>
>>> 							Thanx, Paul
> 
> 
> 

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