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Date: Thu, 13 Dec 2012 13:00:27 +0200
From: Andriy Gapon <avg@FreeBSD.org>
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To: John Baldwin <jhb@FreeBSD.org>
Subject: Re: svn commit: r243764 - head/sys/x86/x86
References: <201212011816.qB1IGE2Y064317@svn.freebsd.org>
 <201212061540.42393.jhb@freebsd.org>
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on 06/12/2012 22:40 John Baldwin said the following:
> On Saturday, December 01, 2012 1:16:14 pm Andriy Gapon wrote:
>> Author: avg
>> Date: Sat Dec  1 18:16:14 2012
>> New Revision: 243764
>> URL: http://svnweb.freebsd.org/changeset/base/243764
>>
>> Log:
>>   ioapic_program_intpin: program high bits before low bits
>>   
>>   Programming the low bits has a side-effect if unmasking the pin if it is
>>   not disabled.  So if an interrupt was pending then it would be delivered
>>   with the correct new vector but to the incorrect old LAPIC.
>>   
>>   This fix could be made clearer by preserving the mask bit while
>>   programming the low bits and then explicitly resetting the mask bit
>>   after all the programming is done.
>>   
>>   Probability to trip over the fixed bug could be increased by bootverbose
>>   because printing of the interrupt information in ioapic_assign_cpu
>>   lengthened the time window during which an interrupt could arrive while
>>   a pin is masked.
> 
> Can you expand the comment to say that you write 'low' second since it may 
> clear the masked bit?
> 

Will do.

-- 
Andriy Gapon