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SubjectRe: [REGRESSION] x86: support for new UV apic
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Ingo Molnar <mingo@elte.hu> writes:

> * Priit Laes <plaes@plaes.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)

Preemption is actually ok here because this runs before the other
CPUs are started

Alternative patch appended.

-Andi

---

Don't warn in read_apic_id() when preemptible but only one CPU online.

Signed-off-by: Andi Kleen <andi@firstfloor.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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