libperf: Centralize map refcnt setting

Currently when a new map is mmapped we set its refcnt to 2 in the
perf_evlist_mmap_ops::mmap callback.

Every mmap gets its refcnt set to 2 when it's first mmaped:

  - 1 for the current user, which will be taken out by a call to
    perf_evlist__munmap_filtered(), where we find out there's
    no more data comming from kernel to this mmap.

  - 1 for the drain code where in perf_mmap__consume() the mmap
    is released if it is empty.

Move this common setup into libperf's generic code before the mmap
callback is called.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20191007125344.14268-23-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/lib/evlist.c

@@ -362,21 +362,6 @@ static int
 perf_evlist__mmap_cb_mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
 			  int output, int cpu)
 {
-	/*
-	 * The last one will be done at perf_mmap__consume(), so that we
-	 * make sure we don't prevent tools from consuming every last event in
-	 * the ring buffer.
-	 *
-	 * I.e. we can get the POLLHUP meaning that the fd doesn't exist
-	 * anymore, but the last events for it are still in the ring buffer,
-	 * waiting to be consumed.
-	 *
-	 * Tools can chose to ignore this at their own discretion, but the
-	 * evlist layer can't just drop it when filtering events in
-	 * perf_evlist__filter_pollfd().
-	 */
-	refcount_set(&map->refcnt, 2);
-
 	return perf_mmap__mmap(map, mp, output, cpu);
 }
 
@@ -418,6 +403,21 @@ mmap_per_evsel(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
 		if (*output == -1) {
 			*output = fd;
 
+			/*
+			 * The last one will be done at perf_mmap__consume(), so that we
+			 * make sure we don't prevent tools from consuming every last event in
+			 * the ring buffer.
+			 *
+			 * I.e. we can get the POLLHUP meaning that the fd doesn't exist
+			 * anymore, but the last events for it are still in the ring buffer,
+			 * waiting to be consumed.
+			 *
+			 * Tools can chose to ignore this at their own discretion, but the
+			 * evlist layer can't just drop it when filtering events in
+			 * perf_evlist__filter_pollfd().
+			 */
+			refcount_set(&map->refcnt, 2);
+
 			if (ops->mmap(map, mp, *output, evlist_cpu) < 0)
 				return -1;
 		} else {

tools/perf/util/mmap.c

@@ -243,21 +243,6 @@ static void perf_mmap__setup_affinity_mask(struct mmap *map, struct mmap_params
 
 int mmap__mmap(struct mmap *map, struct mmap_params *mp, int fd, int cpu)
 {
-	/*
-	 * The last one will be done at perf_mmap__consume(), so that we
-	 * make sure we don't prevent tools from consuming every last event in
-	 * the ring buffer.
-	 *
-	 * I.e. we can get the POLLHUP meaning that the fd doesn't exist
-	 * anymore, but the last events for it are still in the ring buffer,
-	 * waiting to be consumed.
-	 *
-	 * Tools can chose to ignore this at their own discretion, but the
-	 * evlist layer can't just drop it when filtering events in
-	 * perf_evlist__filter_pollfd().
-	 */
-	refcount_set(&map->core.refcnt, 2);
-
 	if (perf_mmap__mmap(&map->core, &mp->core, fd, cpu)) {
 		pr_debug2("failed to mmap perf event ring buffer, error %d\n",
 			  errno);