linux-kernel - Re: [PATCH 04/14] hrtimer: use base->index instead of basenum in switch_hrtimer

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Date:	Wed, 26 Mar 2014 23:27:43 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Viresh Kumar <viresh.kumar@...aro.org>,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, linaro-networking@...aro.org
Subject: Re: [PATCH 04/14] hrtimer: use base->index instead of basenum in
 switch_hrtimer_base()

On 03/26/2014 11:01 PM, Thomas Gleixner wrote:
> On Wed, 26 Mar 2014, Srivatsa S. Bhat wrote:
>> On 03/26/2014 04:51 PM, Viresh Kumar wrote:
>>> In switch_hrtimer_base() we have created a local variable basenum which is set
>>> to base->index. This variable is used at only one place. It makes code more
>>> readable if we remove this variable use base->index directly.
>>>
>>
>> No, this doesn't look right. Note that the code can re-execute
>> the assignment to new_base, by jumping to the 'again' label.
>> See below.
>>
>>> --- a/kernel/hrtimer.c
>>> +++ b/kernel/hrtimer.c
>>> @@ -202,11 +202,10 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
>>>  	struct hrtimer_cpu_base *new_cpu_base;
>>>  	int this_cpu = smp_processor_id();
>>>  	int cpu = get_nohz_timer_target(pinned);
>>> -	int basenum = base->index;
>>>
>>>  again:
>>>  	new_cpu_base = &per_cpu(hrtimer_bases, cpu);
>>> -	new_base = &new_cpu_base->clock_base[basenum];
>>> +	new_base = &new_cpu_base->clock_base[base->index];
>>>
>>
>> Further down, timer->base can be altered (and set to NULL too).
>> So if we jump back to 'again', we'll end up in trouble.
>> So I think its important to cache the value in basenum and
>> use it.
> 
> That's irrelevant. base is not changing.
> 

Sorry, I missed that :-(

Regards,
Srivatsa S. Bhat

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