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

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Date:	Fri, 25 Apr 2008 11:45:26 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	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

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)

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@...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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