linux-kernel - [PATCH v2 1/9] perf thread_map: Skip exited threads when scanning /proc

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Date: Wed, 31 Jan 2024 16:14:55 -0800
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, 
	Ravi Bangoria <ravi.bangoria@....com>, James Clark <james.clark@....com>, 
	Kan Liang <kan.liang@...ux.intel.com>, John Garry <john.g.garry@...cle.com>, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: [PATCH v2 1/9] perf thread_map: Skip exited threads when scanning /proc

Scanning /proc is inherently racy. Scanning /proc/pid/task within that
is also racy as the pid can terminate. Rather than failing in
__thread_map__new_all_cpus, skip pids for such failures.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/thread_map.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/thread_map.c b/tools/perf/util/thread_map.c
index e848579e61a8..18fbc41d09f3 100644
--- a/tools/perf/util/thread_map.c
+++ b/tools/perf/util/thread_map.c
@@ -109,9 +109,10 @@ static struct perf_thread_map *__thread_map__new_all_cpus(uid_t uid)
 
 		snprintf(path, sizeof(path), "/proc/%d/task", pid);
 		items = scandir(path, &namelist, filter, NULL);
-		if (items <= 0)
-			goto out_free_closedir;
-
+		if (items <= 0) {
+			pr_debug("scandir for %d returned empty, skipping\n", pid);
+			continue;
+		}
 		while (threads->nr + items >= max_threads) {
 			max_threads *= 2;
 			grow = true;
@@ -152,8 +153,6 @@ static struct perf_thread_map *__thread_map__new_all_cpus(uid_t uid)
 	for (i = 0; i < items; i++)
 		zfree(&namelist[i]);
 	free(namelist);
-
-out_free_closedir:
 	zfree(&threads);
 	goto out_closedir;
 }
-- 
2.43.0.429.g432eaa2c6b-goog