linux-kernel - Re: [PATCH] x86/fixup_irq: Clean the offlining CPU from the irq affinity mask

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Message-ID: <5062B602.6000502@linux.vnet.ibm.com>
Date:	Wed, 26 Sep 2012 13:30:02 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
CC:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"yanmin_zhang@...ux.intel.com" <yanmin_zhang@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] x86/fixup_irq: Clean the offlining CPU from the irq affinity
 mask

On 09/26/2012 12:22 PM, Liu, Chuansheng wrote:
>>> +		} else if (cpumask_test_cpu(cpu, data->affinity))
>>> +			cpumask_clear_cpu(cpu, data->affinity);
>>>
>>
>> You meant to use 'affinity' (instead of data->affinity) in the above 2 statements
>> right? Note that we do chip->irq_set_affinity(data, affinity, true); further down.
>>
> 
> Yes, I have noticed it, used data->affinity here is just for avoiding compile warning.
> in fact affinity == data->affinity, but affinity pointer is const type,
> And cpumask_clear_cpu needs non-const type,so here I am using data->affinity,
> instead of changing code "const struct cpumask *affinity;"
> 

Hmm.. Then what happens to error handling in the case that you can't set
the affinity?

ie., if we take the 'else' branch in:
                if (chip->irq_set_affinity)
                        chip->irq_set_affinity(data, affinity, true);
                else if (!(warned++))
                        set_affinity = 0;

In that case, we would end up with an incorrect data->affinity right?

Btw, on a slightly different note, I'm also rather surprised that the above
code doesn't care about the return value of chip->irq_set_affinity() ..
Shouldn't we warn if that fails?

Regards,
Srivatsa S. Bhat

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