linux-kernel - [PATCH v6 19/47] perf maps: Add maps__load

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Message-Id: <20231207011722.1220634-20-irogers@google.com>
Date:   Wed,  6 Dec 2023 17:16:53 -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>,
        Nick Terrell <terrelln@...com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        "Steinar H. Gunderson" <sesse@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Colin Ian King <colin.i.king@...il.com>,
        Dmitrii Dolgov <9erthalion6@...il.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Ming Wang <wangming01@...ngson.cn>,
        James Clark <james.clark@....com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Leo Yan <leo.yan@...aro.org>,
        Ravi Bangoria <ravi.bangoria@....com>,
        German Gomez <german.gomez@....com>,
        Changbin Du <changbin.du@...wei.com>,
        Paolo Bonzini <pbonzini@...hat.com>, Li Dong <lidong@...o.com>,
        Sandipan Das <sandipan.das@....com>,
        liuwenyu <liuwenyu7@...wei.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Guilherme Amadio <amadio@...too.org>
Subject: [PATCH v6 19/47] perf maps: Add maps__load_first

Avoid bpf_lock_contention_touching the internal maps data structure by
adding a helper function. As access is done directly on the map in
maps, hold the read lock to stop it being removed.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/bpf_lock_contention.c |  2 +-
 tools/perf/util/maps.c                | 13 +++++++++++++
 tools/perf/util/maps.h                |  2 ++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index f1716c089c99..31ff19afc20c 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -318,7 +318,7 @@ int lock_contention_read(struct lock_contention *con)
 	}
 
 	/* make sure it loads the kernel map */
-	map__load(maps__first(machine->kmaps)->map);
+	maps__load_first(machine->kmaps);
 
 	prev_key = NULL;
 	while (!bpf_map_get_next_key(fd, prev_key, &key)) {
diff --git a/tools/perf/util/maps.c b/tools/perf/util/maps.c
index 986daa1b0497..024a6c9f72c4 100644
--- a/tools/perf/util/maps.c
+++ b/tools/perf/util/maps.c
@@ -793,3 +793,16 @@ int maps__merge_in(struct maps *kmaps, struct map *new_map)
 	}
 	return err;
 }
+
+void maps__load_first(struct maps *maps)
+{
+	struct map_rb_node *first;
+
+	down_read(maps__lock(maps));
+
+	first = maps__first(maps);
+	if (first)
+		map__load(first->map);
+
+	up_read(maps__lock(maps));
+}
diff --git a/tools/perf/util/maps.h b/tools/perf/util/maps.h
index e4a49d6ff5cf..b7ab3ec61b7c 100644
--- a/tools/perf/util/maps.h
+++ b/tools/perf/util/maps.h
@@ -142,4 +142,6 @@ void __maps__sort_by_name(struct maps *maps);
 
 void maps__fixup_end(struct maps *maps);
 
+void maps__load_first(struct maps *maps);
+
 #endif // __PERF_MAPS_H
-- 
2.43.0.rc2.451.g8631bc7472-goog