From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri, 1 May 2009 10:23:17 +0000 (+0200)
Subject: perf_counter: fix nmi-watchdog interaction
X-Git-Tag: v2.6.31-rc1~383^2~316
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=63a809a2dc53b91268dd915bbcbd425063893676;p=platform%2Fkernel%2Flinux-3.10.git

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>
---

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: