perf dso: Use container_of() to avoid a pointer in 'struct dso_data'

The dso pointer in 'struct dso_data' is necessary for reference count
checking to account for the dso_data forming a global list of open dso's
with references to the dso.

The dso pointer also allows for the indirection that reference count
checking needs. Outside of reference count checking the indirection
isn't needed and container_of() is more efficient and saves space.

The reference count won't be increased by placing items onto the global
list, matching how things were before the reference count checking
change, but we assert the dso is in dsos holding it live (and that the
set of open dsos is a subset of all dsos for the machine).

Update the DSO data tests so that they use a dsos struct to make the
invariant true.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Changbin Du <changbin.du@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/20240506180104.485674-5-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 17 insertions, 1 deletions

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 27db65e96e04..dde706b71da7 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -497,14 +497,20 @@ static pthread_mutex_t dso__data_open_lock = PTHREAD_MUTEX_INITIALIZER;
 static void dso__list_add(struct dso *dso)
 {
 	list_add_tail(&dso__data(dso)->open_entry, &dso__data_open);
+#ifdef REFCNT_CHECKING
 	dso__data(dso)->dso = dso__get(dso);
+#endif
+	/* Assume the dso is part of dsos, hence the optional reference count above. */
+	assert(dso__dsos(dso));
 	dso__data_open_cnt++;
 }
 
 static void dso__list_del(struct dso *dso)
 {
 	list_del_init(&dso__data(dso)->open_entry);
+#ifdef REFCNT_CHECKING
 	dso__put(dso__data(dso)->dso);
+#endif
 	WARN_ONCE(dso__data_open_cnt <= 0,
 		  "DSO data fd counter out of bounds.");
 	dso__data_open_cnt--;
@@ -654,9 +660,15 @@ static void close_dso(struct dso *dso)
 static void close_first_dso(void)
 {
 	struct dso_data *dso_data;
+	struct dso *dso;
 
 	dso_data = list_first_entry(&dso__data_open, struct dso_data, open_entry);
-	close_dso(dso_data->dso);
+#ifdef REFCNT_CHECKING
+	dso = dso_data->dso;
+#else
+	dso = container_of(dso_data, struct dso, data);
+#endif
+	close_dso(dso);
 }
 
 static rlim_t get_fd_limit(void)
@@ -1449,7 +1461,9 @@ struct dso *dso__new_id(const char *name, struct dso_id *id)
 		data->fd = -1;
 		data->status = DSO_DATA_STATUS_UNKNOWN;
 		INIT_LIST_HEAD(&data->open_entry);
+#ifdef REFCNT_CHECKING
 		data->dso = NULL; /* Set when on the open_entry list. */
+#endif
 	}
 	return res;
 }
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index f9689dd60de3..df2c98402af3 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -147,7 +147,9 @@ struct dso_cache {
 struct dso_data {
 	struct rb_root	 cache;
 	struct list_head open_entry;
+#ifdef REFCNT_CHECKING
 	struct dso	 *dso;
+#endif
 	int		 fd;
 	int		 status;
 	u32		 status_seen;