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    Subject[PATCH 5.4 42/83] perf/core: fix parent pid/tid in task exit events
    Date
    From: Ian Rogers <irogers@google.com>

    commit f3bed55e850926614b9898fe982f66d2541a36a5 upstream.

    Current logic yields the child task as the parent.

    Before:
    $ perf record bash -c "perf list > /dev/null"
    $ perf script -D |grep 'FORK\|EXIT'
    4387036190981094 0x5a70 [0x30]: PERF_RECORD_FORK(10472:10472):(10470:10470)
    4387036606207580 0xf050 [0x30]: PERF_RECORD_EXIT(10472:10472):(10472:10472)
    4387036607103839 0x17150 [0x30]: PERF_RECORD_EXIT(10470:10470):(10470:10470)
    ^
    Note the repeated values here -------------------/

    After:
    383281514043 0x9d8 [0x30]: PERF_RECORD_FORK(2268:2268):(2266:2266)
    383442003996 0x2180 [0x30]: PERF_RECORD_EXIT(2268:2268):(2266:2266)
    383451297778 0xb70 [0x30]: PERF_RECORD_EXIT(2266:2266):(2265:2265)

    Fixes: 94d5d1b2d891 ("perf_counter: Report the cloning task as parent on perf_counter_fork()")
    Reported-by: KP Singh <kpsingh@google.com>
    Signed-off-by: Ian Rogers <irogers@google.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20200417182842.12522-1-irogers@google.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/events/core.c | 13 ++++++++++---
    1 file changed, 10 insertions(+), 3 deletions(-)

    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -7052,10 +7052,17 @@ static void perf_event_task_output(struc
    goto out;

    task_event->event_id.pid = perf_event_pid(event, task);
    - task_event->event_id.ppid = perf_event_pid(event, current);
    -
    task_event->event_id.tid = perf_event_tid(event, task);
    - task_event->event_id.ptid = perf_event_tid(event, current);
    +
    + if (task_event->event_id.header.type == PERF_RECORD_EXIT) {
    + task_event->event_id.ppid = perf_event_pid(event,
    + task->real_parent);
    + task_event->event_id.ptid = perf_event_pid(event,
    + task->real_parent);
    + } else { /* PERF_RECORD_FORK */
    + task_event->event_id.ppid = perf_event_pid(event, current);
    + task_event->event_id.ptid = perf_event_tid(event, current);
    + }

    task_event->event_id.time = perf_event_clock(event);


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