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

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Date:	Tue, 27 Sep 2011 15:35:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	tglx@...utronix.de, hpa@...or.com, stable@...nel.org,
	tj@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i386/bigsmp: eliminate false warnings regarding logical
 APIC ID mismatches


* 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?

Thanks,

	Ingo
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