On Mon, Sep 08, 2014 at 02:19:52PM +0200, Jiri Olsa wrote: > > I have another 'problem' with 179033b3e064. What if you 'want' to > > continue monitoring after the initial task died? Eg. if you want to > > monitor crap that unconditionally daemonizes. > > right.. did not think of that.. need to check more, but > seems like just the check for children should be enough >
Indeed, that should work.
> ---
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index bf482ccbdbe1..341d0b47ca14 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3568,6 +3568,19 @@ static int perf_event_read_one(struct perf_event
> *event,
> return n * sizeof(u64);
> }
>
> +static bool is_event_hup(struct perf_event *event)
> +{
> + bool no_children;
> +
> + if (event->state != PERF_EVENT_STATE_EXIT)
> + return false;
> +
> + mutex_lock(&event->child_mutex);
> + no_children = list_empty(&event->child_list);
> + mutex_unlock(&event->child_mutex);
> + return no_children;
> +}
> +
> /*
> * Read the performance event - simple non blocking version for now
> */
> @@ -3582,8 +3595,7 @@ perf_read_hw(struct perf_event *event, char __user
> *buf, size_t count)
> * error state (i.e. because it was pinned but it couldn't be
> * scheduled on to the CPU at some point).
> */
> - if ((event->state == PERF_EVENT_STATE_ERROR) ||
> - (event->state == PERF_EVENT_STATE_EXIT))
> + if ((event->state == PERF_EVENT_STATE_ERROR) || (is_event_hup(event)))
> return 0;
Do we want this? It seems like a fairly sensible thing to start a
counter and wait for the thing to die, only to then read the total
count. But with this on we get 0s.
I suppose Stephane's email got to you after you did this and we should
be dropping this thing entirely?
> if (count < event->read_size)
> @@ -3614,7 +3626,7 @@ static unsigned int perf_poll(struct file *file,
> poll_table *wait)
>
> poll_wait(file, &event->waitq, wait);
>
> - if (event->state == PERF_EVENT_STATE_EXIT)
> + if (is_event_hup(event))
> return events;
>
> /*
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