perf, x86: Fix double enable calls

hw_perf_enable() would enable already enabled events.

This causes problems with code that assumes that ->enable/->disable calls
are balanced (like the LBR code does).

What happens is that events that were already running and left in place
would get enabled again.

Avoid this by only enabling new events that match their previous
assignment.

Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 045cc0bb4c17..1d665a0b202c 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -835,6 +835,10 @@ void hw_perf_enable(void)
 			event = cpuc->event_list[i];
 			hwc = &event->hw;
 
+			if (i < n_running &&
+			    match_prev_assignment(hwc, cpuc, i))
+				continue;
+
 			if (hwc->idx == -1)
 				x86_assign_hw_event(event, cpuc, i);