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    Subject[PATCH 3.16.y-ckt 155/180] perf/x86: Fix filter_events() bug with event mappings
    Date
    3.16.7-ckt24 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Stephane Eranian <eranian@google.com>

    commit 61b87cae6361ea6af161c1ffa549898892707b19 upstream.

    This patch fixes a bug in the filter_events() function.

    The patch fixes the bug whereby if some mappings did not
    exist, e.g., STALLED_CYCLES_FRONTEND, then any event after it
    in the attrs array would disappear from the published list of
    events in /sys/devices/cpu/events. This could be verified
    easily on any system post SNB (which do not publish
    STALLED_CYCLES_FRONTEND):

    $ ./perf stat -e cycles,ref-cycles true
    Performance counter stats for 'true':
    1,217,348 cycles
    <not supported> ref-cycles

    The problem is that in filter_events() there is an assumption
    that the argument (attrs) is organized in increasing continuous
    event indexes related to the event_map(). But if we remove the
    non-supported events by shifing the position in the array, then
    the lookup x86_pmu.event_map() needs to compensate for it, otherwise
    we are looking up the wrong index. This patch corrects this problem
    by compensating for the deleted events and with that ref-cycles
    reappears (here shown on Haswell):

    $ perf stat -e ref-cycles,cycles true
    Performance counter stats for 'true':
    4,525,910 ref-cycles
    1,064,920 cycles
    0.002943888 seconds time elapsed

    Signed-off-by: Stephane Eranian <eranian@google.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Cc: jolsa@kernel.org
    Cc: kan.liang@intel.com
    Fixes: 8300daa26755 ("perf/x86: Filter out undefined events from sysfs events attribute")
    Link: http://lkml.kernel.org/r/1449516805-6637-1-git-send-email-eranian@google.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    arch/x86/kernel/cpu/perf_event.c | 11 ++++++++++-
    1 file changed, 10 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
    index 2a6c3859e8a1..7c08f55a07cd 100644
    --- a/arch/x86/kernel/cpu/perf_event.c
    +++ b/arch/x86/kernel/cpu/perf_event.c
    @@ -1386,6 +1386,7 @@ static void __init filter_events(struct attribute **attrs)
    {
    struct device_attribute *d;
    struct perf_pmu_events_attr *pmu_attr;
    + int offset = 0;
    int i, j;

    for (i = 0; attrs[i]; i++) {
    @@ -1394,7 +1395,7 @@ static void __init filter_events(struct attribute **attrs)
    /* str trumps id */
    if (pmu_attr->event_str)
    continue;
    - if (x86_pmu.event_map(i))
    + if (x86_pmu.event_map(i + offset))
    continue;

    for (j = i; attrs[j]; j++)
    @@ -1402,6 +1403,14 @@ static void __init filter_events(struct attribute **attrs)

    /* Check the shifted attr. */
    i--;
    +
    + /*
    + * event_map() is index based, the attrs array is organized
    + * by increasing event index. If we shift the events, then
    + * we need to compensate for the event_map(), otherwise
    + * we are looking up the wrong event in the map
    + */
    + offset++;
    }
    }

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