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

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Date:	Fri, 25 Apr 2008 08:44:06 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Priit Laes <plaes@...es.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Jack Steiner <steiner@....com>
Subject: Re: [REGRESSION] x86: support for new UV apic


* 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?

	Ingo

--------------->
Subject: x86: disable preemption in native_smp_prepare_cpus
From: Ingo Molnar <mingo@...e.hu>
Date: Fri Apr 18 11:07:10 CEST 2008

Priit Laes reported the following warning:

Call Trace:
 [<ffffffff8022f1e1>] warn_on_slowpath+0x51/0x63
 [<ffffffff80282e48>] sys_ioctl+0x2d/0x5d
 [<ffffffff805185ff>] _spin_lock+0xe/0x24
 [<ffffffff80227459>] task_rq_lock+0x3d/0x73
 [<ffffffff805133c3>] set_cpu_sibling_map+0x336/0x350
 [<ffffffff8021c1b8>] read_apic_id+0x30/0x62
 [<ffffffff806d921d>] verify_local_APIC+0x90/0x138
 [<ffffffff806d84b5>] native_smp_prepare_cpus+0x1f9/0x305
 [<ffffffff806ce7b1>] kernel_init+0x59/0x2d9
 [<ffffffff80518a26>] _spin_unlock_irq+0x11/0x2b
 [<ffffffff8020bf48>] child_rip+0xa/0x12
 [<ffffffff806ce758>] kernel_init+0x0/0x2d9
 [<ffffffff8020bf3e>] child_rip+0x0/0x12

fix this by generally disabling preemption in native_smp_prepare_cpus().

Reported-and-bisected-by: Priit Laes <plaes@...es.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/smpboot.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: linux-x86.q/arch/x86/kernel/smpboot.c
===================================================================
--- linux-x86.q.orig/arch/x86/kernel/smpboot.c
+++ linux-x86.q/arch/x86/kernel/smpboot.c
@@ -1181,6 +1181,7 @@ static void __init smp_cpu_index_default
  */
 void __init native_smp_prepare_cpus(unsigned int max_cpus)
 {
+	preempt_disable();
 	nmi_watchdog_default();
 	smp_cpu_index_default();
 	current_cpu_data = boot_cpu_data;
@@ -1197,7 +1198,7 @@ void __init native_smp_prepare_cpus(unsi
 	if (smp_sanity_check(max_cpus) < 0) {
 		printk(KERN_INFO "SMP disabled\n");
 		disable_smp();
-		return;
+		goto out;
 	}
 
 	preempt_disable();
@@ -1237,6 +1238,8 @@ void __init native_smp_prepare_cpus(unsi
 	printk(KERN_INFO "CPU%d: ", 0);
 	print_cpu_info(&cpu_data(0));
 	setup_boot_clock();
+out:
+	preempt_enable();
 }
 /*
  * Early setup to make printk work.
--
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