linux-kernel - Re: [BUG] perf: cannot read counts in per-process mode in 3.17-rcX

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Date:	Mon, 8 Sep 2014 14:49:45 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [BUG] perf: cannot read counts in per-process mode in 3.17-rcX

On Mon, Sep 08, 2014 at 02:35:06PM +0200, Stephane Eranian wrote:
> Hi,
> 
> It seems something is seriously broken with perf_events in
> 3.17-rcX. I have tried rc3, rc4. No way to get any counts
> out using perf stat in per-process mode. I am trying on Intel
> and the PMU is correctly detected:
> 
> $ perf stat -e cycles ls
>       <not counted> cycles
> 
> It is not a permission problem. It is a read problem!
> $ strace perf stat -e cycles ls
> 
> perf_event_open(0x27d7e20, 2261, -1, -1, 0x8 /* PERF_FLAG_??? */) = 3
> write(6, "\0", 1)                       = 1
> close(6)                                = 0
> wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 2261
> --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2261,
> si_status=0, si_utime=0, si_stime=0} ---
> rt_sigreturn()                          = 2261
> read(3, "", 24)                         = 0
>  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

ouch thats me.. sry :-\

the PERF_EVENT_STATE_EXIT check should not go to the
read path.. could you please test attached patch?

jirka


---
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d8cb4d2..6d1c9ce 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)
--
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