linux-kernel - Re: [PATCH] lockdep: call trace_hardirqs_off after clearing hardirqs

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Date:   Tue, 14 Mar 2017 09:24:17 +0800
From:   qhou <qi.hou@...driver.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     <mingo@...hat.com>, <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>, <C.Emde@...dl.org>,
        <paul.gortmaker@...driver.com>, <bruce.ashfield@...driver.com>
Subject: Re: [PATCH] lockdep: call trace_hardirqs_off after clearing
 hardirqs_enabled



On 2017年03月13日 22:05, Steven Rostedt wrote:
> On Mon, 13 Mar 2017 18:08:48 +0800
> Qi Hou <qi.hou@...driver.com> wrote:
>
>> The current order of calls within trace_hardirqs_off() would provoke an
>> "unannotated irqs-off" WARNING.
>>
>> This warning was reported by check_flags() when it found that the hardirqs has
>> been disabled but the irq-flags state, hardirqs_enabled, has not been cleared.
>>
>> Check_flags() is called via trace_hardirqs_off(), and trace_hardirqs_off() will
>> be called by functions kind of local_irq_disable() if CONFIG_TRACE_IRQFLAGS has
>> been enabled.
>>
>> The calltrace from functions kind of local_irq_diasble() to check_flags()
>> simplied as below:
>>
>> local_irq_disable()
>>   |- trace_hardirqs_off()
>>       |- trace_hardirqs_off_caller()
>>           |- preemptirqsoff_hist()
> There is no preemptirqsoff_hist() function in the kernel.
Sorry, it's a mistake. It should have been 
"trace_hardirqs_off_caller()", defined in file
kernel/locking/lockdep.c.

And it will call trace_preemptirqsoff_hist_rcuidle(), 
trace_preemptirqsoff_hist_rcuidle will()
call check_flags().

I will correct it. And after carefully checking the patch, I will 
re-send it.

Very very sorry for my mistake. That wasted your time.

---
Best regards,
Qi Hou
>
> -- Steve
>
>>              |- __DO_TRACE()
>>                 |- rcu_dereference_sched()
>>                     |- rcu_read_lock_sched_held()
>>                         |- lock_is_held()
>>                             |- check_flags()
>>
>> The order of calls within trace_hardirqs_off() can be simplified as below:
>>
>> local_irq_disable()
>>   |- raw_local_irq_disable()
>>   |- trace_hardirqs_off()
>>       |- trace_hardirqs_off() --> check_flags()
>>       |- hardirqs_enabled = 0
>>
>> We could find that the call to check_flags() has been made between disabling
>> hardirqs and clearing hardirqs_enabled. That will definitely cause an
>> "unannotated irqs-off" warning.
>>
>> To fix this "unannotated irqs-off" warning, we must call trace_hardirqs_off()
>> after that we clear hardirqs_enabled.
>>
>> Signed-off-by: Qi Hou <qi.hou@...driver.com>
>> ---
>>   kernel/locking/lockdep.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
>> index 577f026..e8b35e4 100644
>> --- a/kernel/locking/lockdep.c
>> +++ b/kernel/locking/lockdep.c
>> @@ -2627,8 +2627,6 @@ __visible void trace_hardirqs_off_caller(unsigned long ip)
>>   {
>>   	struct task_struct *curr = current;
>>   
>> -	time_hardirqs_off(CALLER_ADDR0, ip);
>> -
>>   	if (unlikely(!debug_locks || current->lockdep_recursion))
>>   		return;
>>   
>> @@ -2649,6 +2647,8 @@ __visible void trace_hardirqs_off_caller(unsigned long ip)
>>   		debug_atomic_inc(hardirqs_off_events);
>>   	} else
>>   		debug_atomic_inc(redundant_hardirqs_off);
>> +
>> +	time_hardirqs_off(CALLER_ADDR0, ip);
>>   }
>>   EXPORT_SYMBOL(trace_hardirqs_off_caller);
>>   

-- 
Best regards,
Qi Hou
Phone number: +86-10-8477-8608
Address: Floor 15, Building B, Wangjing Plaza, No.9 Zhong-Huan Nanlu, Chaoyang District