Gitweb:     http://git.kernel.org/linus/219a92a4c40db2fac604f63bce9a5a3fe1967879
Commit:     219a92a4c40db2fac604f63bce9a5a3fe1967879
Parent:     2aa72f612144a0a7d4b0b22ae7c122692ac6a013
Author:     Matt Evans <matt@ozlabs.org>
AuthorDate: Mon Jul 5 17:36:32 2010 +0000
Committer:  Benjamin Herrenschmidt <benh@kernel.crashing.org>
CommitDate: Thu Jul 8 18:11:37 2010 +1000

    powerpc/perf_event: Fix for power_pmu_disable()
    
    When power_pmu_disable() removes the given event from a particular index into
    cpuhw->event[], it shuffles down higher event[] entries.  But, this array is
    paired with cpuhw->events[] and cpuhw->flags[] so should shuffle them
    similarly.
    
    If these arrays get out of sync, code such as power_check_constraints() will
    fail.  This caused a bug where events were temporarily disabled and then failed
    to be re-enabled; subsequent code tried to write_pmc() with its (disabled) idx
    of 0, causing a message "oops trying to write PMC0".  This triggers this bug on
    POWER7, running a miss-heavy test:
    
      perf record -e L1-dcache-load-misses -e L1-dcache-store-misses ./misstest
    
    Signed-off-by: Matt Evans <matt@ozlabs.org>
    Acked-by: Paul Mackerras <paulus@samba.org>
    Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 arch/powerpc/kernel/perf_event.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c
index 43b83c3..5c14ffe 100644
--- a/arch/powerpc/kernel/perf_event.c
+++ b/arch/powerpc/kernel/perf_event.c
@@ -791,8 +791,11 @@ static void power_pmu_disable(struct perf_event *event)
 	cpuhw = &__get_cpu_var(cpu_hw_events);
 	for (i = 0; i < cpuhw->n_events; ++i) {
 		if (event == cpuhw->event[i]) {
-			while (++i < cpuhw->n_events)
+			while (++i < cpuhw->n_events) {
 				cpuhw->event[i-1] = cpuhw->event[i];
+				cpuhw->events[i-1] = cpuhw->events[i];
+				cpuhw->flags[i-1] = cpuhw->flags[i];
+			}
 			--cpuhw->n_events;
 			ppmu->disable_pmc(event->hw.idx - 1, cpuhw->mmcr);
 			if (event->hw.idx) {
--
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