[tip:perf/urgent] perf, x86: Fix double enable calls

[tip-bot for Peter Zijlstra]

Commit-ID:  f3d46b2e6fa57547f9884330798792afc83f4b04
Gitweb:     http://git.kernel.org/tip/f3d46b2e6fa57547f9884330798792afc83f4b04
Author:     Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Sat, 6 Mar 2010 13:24:58 +0100
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Wed, 10 Mar 2010 13:22:35 +0100

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 <a.p.zijlstra@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxx>
Cc: paulus@xxxxxxxxx
Cc: eranian@xxxxxxxxxx
Cc: robert.richter@xxxxxxx
Cc: fweisbec@xxxxxxxxx
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 arch/x86/kernel/cpu/perf_event.c |    4 ++++
 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 045cc0b..1d665a0 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);
 
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