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

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Date:	Tue, 27 Sep 2011 16:42:19 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jan Beulich <JBeulich@...e.com>
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


* Jan Beulich <JBeulich@...e.com> wrote:

> >>> 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.

Yeah, i think it would be fine that way. If you think there's a 
chance of something breaking or complaints coming up then you can 
split it into two patches: the first one factors out the function, 
the second one does the change.

Thanks,

	Ingo
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