[PATCH 3/8] perf mmap: Be consistent when checking for an unmaped ring buffer

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

The previous patch is insufficient to cure the reported 'perf trace'
segfault, as it only cures the perf_mmap__read_done() case, moving the
segfault to perf_mmap__read_init() functio, fix it by doing the same
refcount check.

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Fixes: 8872481bd048 ("perf mmap: Introduce perf_mmap__read_init()")
Link: https://lkml.kernel.org/r/20180326144127.GF18897@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/mmap.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
index f6cfc52ff1fe..fc832676a798 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -234,7 +234,7 @@ static int overwrite_rb_find_range(void *buf, int mask, u64 *start, u64 *end)
 /*
  * Report the start and end of the available data in ringbuffer
  */
-int perf_mmap__read_init(struct perf_mmap *md)
+static int __perf_mmap__read_init(struct perf_mmap *md)
 {
 	u64 head = perf_mmap__read_head(md);
 	u64 old = md->prev;
@@ -268,6 +268,17 @@ int perf_mmap__read_init(struct perf_mmap *md)
 	return 0;
 }
 
+int perf_mmap__read_init(struct perf_mmap *map)
+{
+	/*
+	 * Check if event was unmapped due to a POLLHUP/POLLERR.
+	 */
+	if (!refcount_read(&map->refcnt))
+		return -ENOENT;
+
+	return __perf_mmap__read_init(map);
+}
+
 int perf_mmap__push(struct perf_mmap *md, void *to,
 		    int push(void *to, void *buf, size_t size))
 {
-- 
2.14.3