linux-kernel - Re: [REGRESSION] x86: support for new UV apic

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Date:	Fri, 25 Apr 2008 13:41:06 +0200
From:	Gabriel C <nix.or.die@...glemail.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>, Priit Laes <plaes@...es.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jack Steiner <steiner@....com>
Subject: Re: [REGRESSION] x86: support for new UV apic

Gabriel C wrote:
> Andi Kleen wrote:
>> Ingo Molnar <mingo@...e.hu> writes:
>>
>>> * Priit Laes <plaes@...es.org> wrote:
>>>
>>>> Hey,
>>>>
>>>> I am getting two following warnings (probable one per each CPU core) 
>>>> using the latest Linus's git:
>>>>
>>>> WARNING: at arch/x86/kernel/genapic_64.c:86 read_apic_id+0x30/0x62()
>>>> Modules linked in:
>>>> Pid: 1, comm: swapper Not tainted 2.6.25-03563-gf7288b1 #20
>>> thanks - could you check the patch below, does it fix the warnings?
>> I think it would have been better to change the WARN_ON to
>>
>> WARN_ON(preemptible() && num_online_cpus() > 1)
> 
> Hmm , I think you are right , Ingo's patch fixes the warning on boot but now I get one when I reboot the box.
> 
>> Preemption is actually ok here because this runs before the other
>> CPUs are started
>>
>> Alternative patch appended.
> 
> I will test your patch in some minutes.

Your patch works better , at least for my box , 4 reboots with your patch and boot/reboot warnings are all gone.


>>
>> Don't warn in read_apic_id() when preemptible but only one CPU online.
>>
>> Signed-off-by: Andi Kleen <andi@...stfloor.org>
>>
>> Index: linux/arch/x86/kernel/genapic_64.c
>> ===================================================================
>> --- linux.orig/arch/x86/kernel/genapic_64.c
>> +++ linux/arch/x86/kernel/genapic_64.c
>> @@ -83,7 +83,7 @@ unsigned int read_apic_id(void)
>>  {
>>  	unsigned int id;
>>  
>> -	WARN_ON(preemptible());
>> +	WARN_ON(preemptible() && num_online_cpus() > 1);
>>  	id = apic_read(APIC_ID);
>>  	if (uv_system_type >= UV_X2APIC)
>>  		id  |= __get_cpu_var(x2apic_extra_bits);
> 
> 
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