[PATCH] x86: fix boot crash in NMI watchdog with CONFIG_CPUMASK_OFFSTACK=y and flat APIC

From: Rusty Russell
Date: Tue Apr 21 2009 - 02:31:07 EST


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.

LKML Message-ID: <alpine.DEB.2.00.0904202113520.10097@xxxxxxxxxxxxxxxxxxx>
Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
---
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
--- 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,
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);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/