[tip:perfcounters/core] perf_counter: fix nmi-watchdog interaction

[tip-bot for Peter Zijlstra <a.p.zijlstra@chello.nl>]

Commit-ID:  63a809a2dc53b91268dd915bbcbd425063893676
Gitweb:     http://git.kernel.org/tip/63a809a2dc53b91268dd915bbcbd425063893676
Author:     Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 1 May 2009 12:23:17 +0200
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 1 May 2009 13:23:44 +0200

perf_counter: fix nmi-watchdog interaction

When we don't have any perf-counters active, don't act like we know
what the NMI is for.

[ Impact: fix hard hang with nmi_watchdog=2 ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090501102533.109867793@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
 arch/x86/kernel/cpu/perf_counter.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index fc06f4d..d4c0cc9 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -871,6 +871,9 @@ perf_counter_nmi_handler(struct notifier_block *self,
 	struct pt_regs *regs;
 	int ret;
 
+	if (!atomic_read(&num_counters))
+		return NOTIFY_DONE;
+
 	switch (cmd) {
 	case DIE_NMI:
 	case DIE_NMI_IPI: