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Date:   Wed,  6 Dec 2023 17:17:02 -0800
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Subject: [PATCH v6 28/47] perf maps: Locking tidy up of nr_maps
From:   Ian Rogers <irogers@google.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Ian Rogers <irogers@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Nick Terrell <terrelln@fb.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kajol Jain <kjain@linux.ibm.com>,
        Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        "Steinar H. Gunderson" <sesse@google.com>,
        Liam Howlett <liam.howlett@oracle.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Colin Ian King <colin.i.king@gmail.com>,
        Dmitrii Dolgov <9erthalion6@gmail.com>,
        Yang Jihong <yangjihong1@huawei.com>,
        Ming Wang <wangming01@loongson.cn>,
        James Clark <james.clark@arm.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        Sean Christopherson <seanjc@google.com>,
        Leo Yan <leo.yan@linaro.org>,
        Ravi Bangoria <ravi.bangoria@amd.com>,
        German Gomez <german.gomez@arm.com>,
        Changbin Du <changbin.du@huawei.com>,
        Paolo Bonzini <pbonzini@redhat.com>, Li Dong <lidong@vivo.com>,
        Sandipan Das <sandipan.das@amd.com>,
        liuwenyu <liuwenyu7@huawei.com>, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org,
        Guilherme Amadio <amadio@gentoo.org>
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Precedence: bulk

After this change maps__nr_maps is only used by tests, existing users
are migrated to maps__empty. Compute maps__empty under the read lock.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/machine.c |  2 +-
 tools/perf/util/maps.c    | 10 ++++++++--
 tools/perf/util/maps.h    |  4 ++--
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 4911734411b5..3da92f18814a 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -440,7 +440,7 @@ static struct thread *findnew_guest_code(struct machine *machine,
 		return NULL;
 
 	/* Assume maps are set up if there are any */
-	if (maps__nr_maps(thread__maps(thread)))
+	if (!maps__empty(thread__maps(thread)))
 		return thread;
 
 	host_thread = machine__find_thread(host_machine, -1, pid);
diff --git a/tools/perf/util/maps.c b/tools/perf/util/maps.c
index c08e412a4313..cb52de9d6c2a 100644
--- a/tools/perf/util/maps.c
+++ b/tools/perf/util/maps.c
@@ -528,7 +528,13 @@ void maps__remove(struct maps *maps, struct map *map)
 
 bool maps__empty(struct maps *maps)
 {
-	return maps__nr_maps(maps) == 0;
+	bool res;
+
+	down_read(maps__lock(maps));
+	res = maps__nr_maps(maps) == 0;
+	up_read(maps__lock(maps));
+
+	return res;
 }
 
 bool maps__equal(struct maps *a, struct maps *b)
@@ -852,7 +858,7 @@ int maps__copy_from(struct maps *dest, struct maps *parent)
 
 	parent_maps_by_address = maps__maps_by_address(parent);
 	n = maps__nr_maps(parent);
-	if (maps__empty(dest)) {
+	if (maps__nr_maps(dest) == 0) {
 		/* No existing mappings so just copy from parent to avoid reallocs in insert. */
 		unsigned int nr_maps_allocated = RC_CHK_ACCESS(parent)->nr_maps_allocated;
 		struct map **dest_maps_by_address =
diff --git a/tools/perf/util/maps.h b/tools/perf/util/maps.h
index 4bcba136ffe5..d9aa62ed968a 100644
--- a/tools/perf/util/maps.h
+++ b/tools/perf/util/maps.h
@@ -43,8 +43,8 @@ int maps__for_each_map(struct maps *maps, int (*cb)(struct map *map, void *data)
 void maps__remove_maps(struct maps *maps, bool (*cb)(struct map *map, void *data), void *data);
 
 struct machine *maps__machine(const struct maps *maps);
-unsigned int maps__nr_maps(const struct maps *maps);
-refcount_t *maps__refcnt(struct maps *maps);
+unsigned int maps__nr_maps(const struct maps *maps); /* Test only. */
+refcount_t *maps__refcnt(struct maps *maps); /* Test only. */
 
 #ifdef HAVE_LIBUNWIND_SUPPORT
 void *maps__addr_space(const struct maps *maps);
-- 
2.43.0.rc2.451.g8631bc7472-goog