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>

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 fc06f4d32644..d4c0cc9d3263 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: