From 2f537a9f8e82f55c241b002c8cfbf34303b45ada Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Tue, 21 Apr 2009 16:00:15 +0930
Subject: [PATCH] x86: fix boot crash in NMI watchdog with
CONFIG_CPUMASK_OFFSTACK=y and flat APIC
fcef8576d8a64fc603e719c97d423f9f6d4e0e8b converted backtrace_mask to a
cpumask_var_t, and assumed check_nmi_watchdog was called before
nmi_watchdog_tick was ever called. Steven's oops shows I was wrong.
This is something of a bandaid: I'm not sure we *should* be calling
nmi_watchdog_tick before check_nmi_watchdog. Note that gcc eliminates
this test for the CONFIG_CPUMASK_OFFSTACK=n case.
[ Impact: fix boot crash in rare configs ]
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <alpine.DEB.2.00.0904202113520.10097@gandalf.stny.rr.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/apic/nmi.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c
index d6bd62407152..2ba52f35a88c 100644
--- a/arch/x86/kernel/apic/nmi.c
+++ b/arch/x86/kernel/apic/nmi.c
@@ -414,7 +414,8 @@ nmi_watchdog_tick(struct pt_regs *regs, unsigned reason)
touched = 1;
}
- if (cpumask_test_cpu(cpu, backtrace_mask)) {
+ /* We can be called before check_nmi_watchdog, hence NULL check. */
+ if (backtrace_mask != NULL && cpumask_test_cpu(cpu, backtrace_mask)) {
static DEFINE_SPINLOCK(lock); /* Serialise the printks */
spin_lock(&lock);
--
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