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    Subject[PATCH 4.16 185/272] perf/core: Fix perf_output_read_group()
    Date
    4.16-stable review patch.  If anyone has any objections, please let me know.

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

    From: Peter Zijlstra <peterz@infradead.org>

    [ Upstream commit 9e5b127d6f33468143d90c8a45ca12410e4c3fa7 ]

    Mark reported his arm64 perf fuzzer runs sometimes splat like:

    armv8pmu_read_counter+0x1e8/0x2d8
    armpmu_event_update+0x8c/0x188
    armpmu_read+0xc/0x18
    perf_output_read+0x550/0x11e8
    perf_event_read_event+0x1d0/0x248
    perf_event_exit_task+0x468/0xbb8
    do_exit+0x690/0x1310
    do_group_exit+0xd0/0x2b0
    get_signal+0x2e8/0x17a8
    do_signal+0x144/0x4f8
    do_notify_resume+0x148/0x1e8
    work_pending+0x8/0x14

    which asserts that we only call pmu::read() on ACTIVE events.

    The above callchain does:

    perf_event_exit_task()
    perf_event_exit_task_context()
    task_ctx_sched_out() // INACTIVE
    perf_event_exit_event()
    perf_event_set_state(EXIT) // EXIT
    sync_child_event()
    perf_event_read_event()
    perf_output_read()
    perf_output_read_group()
    leader->pmu->read()

    Which results in doing a pmu::read() on an !ACTIVE event.

    I _think_ this is 'new' since we added attr.inherit_stat, which added
    the perf_event_read_event() to the exit path, without that
    perf_event_read_output() would only trigger from samples and for
    @event to trigger a sample, it's leader _must_ be ACTIVE too.

    Still, adding this check makes it consistent with the @sub case for
    the siblings.

    Reported-and-Tested-by: Mark Rutland <mark.rutland@arm.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    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>
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    kernel/events/core.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -5770,7 +5770,8 @@ static void perf_output_read_group(struc
    if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
    values[n++] = running;

    - if (leader != event)
    + if ((leader != event) &&
    + (leader->state == PERF_EVENT_STATE_ACTIVE))
    leader->pmu->read(leader);

    values[n++] = perf_event_count(leader);

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