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    Subject[PATCH 4.14 089/101] perf/core: Fix ctx_event_type in ctx_resched()
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Song Liu <songliubraving@fb.com>

    commit bd903afeb504db5655a45bb4cf86f38be5b1bf62 upstream.

    In ctx_resched(), EVENT_FLEXIBLE should be sched_out when EVENT_PINNED is
    added. However, ctx_resched() calculates ctx_event_type before checking
    this condition. As a result, pinned events will NOT get higher priority
    than flexible events.

    The following shows this issue on an Intel CPU (where ref-cycles can
    only use one hardware counter).

    1. First start:
    perf stat -C 0 -e ref-cycles -I 1000
    2. Then, in the second console, run:
    perf stat -C 0 -e ref-cycles:D -I 1000

    The second perf uses pinned events, which is expected to have higher
    priority. However, because it failed in ctx_resched(). It is never
    run.

    This patch fixes this by calculating ctx_event_type after re-evaluating
    event_type.

    Reported-by: Ephraim Park <ephiepark@fb.com>
    Signed-off-by: Song Liu <songliubraving@fb.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: <jolsa@redhat.com>
    Cc: <kernel-team@fb.com>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Fixes: 487f05e18aa4 ("perf/core: Optimize event rescheduling on active contexts")
    Link: http://lkml.kernel.org/r/20180306055504.3283731-1-songliubraving@fb.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/events/core.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -2322,7 +2322,7 @@ static void ctx_resched(struct perf_cpu_
    struct perf_event_context *task_ctx,
    enum event_type_t event_type)
    {
    - enum event_type_t ctx_event_type = event_type & EVENT_ALL;
    + enum event_type_t ctx_event_type;
    bool cpu_event = !!(event_type & EVENT_CPU);

    /*
    @@ -2332,6 +2332,8 @@ static void ctx_resched(struct perf_cpu_
    if (event_type & EVENT_PINNED)
    event_type |= EVENT_FLEXIBLE;

    + ctx_event_type = event_type & EVENT_ALL;
    +
    perf_pmu_disable(cpuctx->ctx.pmu);
    if (task_ctx)
    task_ctx_sched_out(cpuctx, task_ctx, event_type);

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