linux-kernel - Re: [PATCH] i386/bigsmp: eliminate false warnings regarding logical APIC ID mismatches

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Date:	Tue, 27 Sep 2011 15:39:20 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	<stable@...nel.org>, <tj@...nel.org>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH] i386/bigsmp: eliminate false warnings regarding
	 logical APIC ID mismatches

>>> On 27.09.11 at 15:35, Ingo Molnar <mingo@...e.hu> wrote:

> * Jan Beulich <JBeulich@...ell.com> wrote:
> 
>> These warnings (generally one per CPU) are a result of initializing
>> x86_cpu_to_logical_apicid while apic_default is still in use, but the
>> check in setup_local_APIC() being done when apic_bigsmp was already
>> used as an override in default_setup_apic_routing():
>> 
>> Overriding APIC driver with bigsmp
>> Enabling APIC mode:  Physflat.  Using 5 I/O APICs
>> ------------[ cut here ]------------
>> WARNING: at .../arch/x86/kernel/apic/apic.c:1239 
> setup_local_APIC+0x137/0x46b()
>> Hardware name: ...
>> CPU0 logical APIC ID: 1 != 0
>> Pid: 1, comm: swapper Not tainted 3.0.1-2011-08-09-jb #2
>> Call Trace:
>>  [<c1005f91>] try_stack_unwind+0x1b1/0x1f0
>>  [<c1004cc7>] dump_trace+0x47/0x110
>>  [<c1005b0b>] show_trace_log_lvl+0x4b/0x60
>>  [<c1005b38>] show_trace+0x18/0x20
>>  [<c1261435>] dump_stack+0x6d/0x72
>>  [<c10355f7>] warn_slowpath_common+0x77/0xb0
>>  [<c10356c3>] warn_slowpath_fmt+0x33/0x40
>>  [<c13fda81>] setup_local_APIC+0x137/0x46b
>>  [<c13d1733>] native_smp_prepare_cpus+0x108/0x1cd
>>  [<c13c61ff>] kernel_init+0x37/0x12c
>>  [<c1264826>] kernel_thread_helper+0x6/0xd
>> ---[ end trace 4eaa2a86a8e2da22 ]---
>> ...
>> CPU 1 irqstacks, hard=f1c9a000 soft=f1c9c000
>> Booting Node   0, Processors  #1
>> smpboot cpu 1: start_ip = 9e000
>> Initializing CPU#1
>> ------------[ cut here ]------------
>> WARNING: at .../arch/x86/kernel/apic/apic.c:1239 
> setup_local_APIC+0x137/0x46b()
>> Hardware name: ...
>> CPU1 logical APIC ID: 2 != 8
>> ...
>> 
>> Fix this (for the time being, i.e. until x86_32_early_logical_apicid()
>> will get removed again, as Tehun says ought to be possible) by
>> overriding the previously stored values at the point where the APIC
>> driver gets overridden.
>> 
>> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
>> Cc: Tejun Heo <tj@...nel.org>
>> Cc: stable@...nel.org (2.6.39 and onwards)
>> 
>> ---
>>  arch/x86/kernel/apic/probe_32.c |   11 +++++++++++
>>  1 file changed, 11 insertions(+)
>> 
>> --- 3.1-rc2/arch/x86/kernel/apic/probe_32.c
>> +++ 3.1-rc2-i386-bigsmp-early-lapicid-override/arch/x86/kernel/apic/probe_32.c
>> @@ -203,7 +203,18 @@ void __init default_setup_apic_routing(v
>>  	if (!cmdline_apic && apic == &apic_default) {
>>  		struct apic *bigsmp = generic_bigsmp_probe();
>>  		if (bigsmp) {
>> +			unsigned int cpu;
>> +
>>  			apic = bigsmp;
>> +			for_each_possible_cpu(cpu) {
>> +				if (early_per_cpu(x86_cpu_to_logical_apicid,
>> +						  cpu) == BAD_APICID)
>> +					continue;
>> +				early_per_cpu(x86_cpu_to_logical_apicid,
>> +					      cpu) =
>> +					bigsmp->x86_32_early_logical_apicid
>> +						(cpu);
>> +			}
>>  			printk(KERN_INFO "Overriding APIC driver with %s\n",
>>  			       apic->name);
>>  		}
> 
> This could move into a separate function i suspect, which would 
> de-uglify it quite significantly?

If that's the only concern, then sure - I'll re-submit with this broken out.

Jan

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