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

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fcef8576d8 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>
This commit is contained in:
Rusty Russell 2009-04-21 16:00:15 +09:30 committed by Ingo Molnar
parent 06c38d5e36
commit 2f537a9f8e
1 changed files with 2 additions and 1 deletions
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3
arch/x86/kernel/apic/nmi.c
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@ -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);