linux-kernel - [PATCH 3.16 355/366] perf thread_map: Use readdir() instead of deprecated readdir

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Date:   Sun, 11 Nov 2018 19:49:05 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Wang Nan" <wangnan0@...wei.com>,
        "Adrian Hunter" <adrian.hunter@...el.com>,
        "David Ahern" <dsahern@...il.com>,
        "Arnaldo Carvalho de Melo" <acme@...hat.com>,
        "Jiri Olsa" <jolsa@...nel.org>,
        "Namhyung Kim" <namhyung@...nel.org>
Subject: [PATCH 3.16 355/366] perf thread_map: Use readdir() instead of
 deprecated readdir_r()

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Arnaldo Carvalho de Melo <acme@...hat.com>

commit 3354cf71104de49326d19d2f9bdb1f66eea52ef4 upstream.

The readdir() function is thread safe as long as just one thread uses a
DIR, which is the case in thread_map, so, to avoid breaking the build
with glibc-2.23.90 (upcoming 2.24), use it instead of readdir_r().

See: http://man7.org/linux/man-pages/man3/readdir.3.html

"However, in modern implementations (including the glibc implementation),
concurrent calls to readdir() that specify different directory streams
are thread-safe.  In cases where multiple threads must read from the
same directory stream, using readdir() with external synchronization is
still preferable to the use of the deprecated readdir_r(3) function."

Noticed while building on a Fedora Rawhide docker container.

Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: David Ahern <dsahern@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Wang Nan <wangnan0@...wei.com>
Link: http://lkml.kernel.org/n/tip-del8h2a0f40z75j4r42l96l0@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 tools/perf/util/thread_map.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/tools/perf/util/thread_map.c
+++ b/tools/perf/util/thread_map.c
@@ -64,7 +64,7 @@ struct thread_map *thread_map__new_by_ui
 	DIR *proc;
 	int max_threads = 32, items, i;
 	char path[256];
-	struct dirent dirent, *next, **namelist = NULL;
+	struct dirent *dirent, **namelist = NULL;
 	struct thread_map *threads = malloc(sizeof(*threads) +
 					    max_threads * sizeof(pid_t));
 	if (threads == NULL)
@@ -76,16 +76,16 @@ struct thread_map *thread_map__new_by_ui
 
 	threads->nr = 0;
 
-	while (!readdir_r(proc, &dirent, &next) && next) {
+	while ((dirent = readdir(proc)) != NULL) {
 		char *end;
 		bool grow = false;
 		struct stat st;
-		pid_t pid = strtol(dirent.d_name, &end, 10);
+		pid_t pid = strtol(dirent->d_name, &end, 10);
 
 		if (*end) /* only interested in proper numerical dirents */
 			continue;
 
-		snprintf(path, sizeof(path), "/proc/%s", dirent.d_name);
+		snprintf(path, sizeof(path), "/proc/%s", dirent->d_name);
 
 		if (stat(path, &st) != 0)
 			continue;