linux-kernel - [PATCH] x86: avoid theoretical spurious NMI backtraces with CONFIG_CPUMASK

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Message-Id: <200904211603.41980.rusty@rustcorp.com.au>
Date:	Tue, 21 Apr 2009 16:03:41 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] x86: avoid theoretical spurious NMI backtraces with CONFIG_CPUMASK_OFFSTACK=y

In theory (though not shown in practice) alloc_cpumask_var() doesn't zero
memory, so CPUs might print an "NMI backtrace for cpu %d" once on boot.

(Bug introduced in fcef8576d8a64fc603e719c97d423f9f6d4e0e8b).

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
---
 arch/x86/kernel/apic/nmi.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c
--- a/arch/x86/kernel/apic/nmi.c
+++ b/arch/x86/kernel/apic/nmi.c
@@ -138,7 +138,7 @@ int __init check_nmi_watchdog(void)
 	if (!prev_nmi_count)
 		goto error;
 
-	alloc_cpumask_var(&backtrace_mask, GFP_KERNEL);
+	alloc_cpumask_var(&backtrace_mask, GFP_KERNEL|__GFP_ZERO);
 	printk(KERN_INFO "Testing NMI watchdog ... ");
 
 #ifdef CONFIG_SMP
--
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