Re: [PATCH] perf: Do not check PERF_EVENT_STATE_EXIT on syscall read path

From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Stephane Eranian <eranian@google.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"mingo@elte.hu" <mingo@elte.hu>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>,
	"ak@linux.intel.com" <ak@linux.intel.com>,
	David Ahern <dsahern@gmail.com>
Subject: Re: [PATCH] perf: Do not check PERF_EVENT_STATE_EXIT on syscall read path
Date: Mon, 8 Sep 2014 17:22:06 +0200	[thread overview]
Message-ID: <20140908152206.GH6758@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20140908143107.GG17728@krava.brq.redhat.com>

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On Mon, Sep 08, 2014 at 04:31:07PM +0200, Jiri Olsa wrote:
> Revert PERF_EVENT_STATE_EXIT check on read syscall path.
> It breaks standard way to read counter, which is to open
> the counter, wait for the monitored process to die and
> read the counter.
> 
> Reported-by: Stephane Eranian <eranian@google.com>
> Acked-by: Stephane Eranian <eranian@google.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Stephane Eranian <eranian@google.com>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

Thanks! 

> ---
>  kernel/events/core.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index d8cb4d21a346..6d1c9ce1643e 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3600,8 +3600,7 @@ 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)
>  		return 0;
>  
>  	if (count < event->read_size)
> -- 
> 1.8.3.1
> 

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