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 <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Athira Rajeev <[e-mail]>
Cc: Changbin Du <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Tiezhu Yang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/tests/dso-data.c

···
 #include <sys/resource.h>
 #include <api/fs/fs.h>
 #include "dso.h"
+#include "dsos.h"
 #include "machine.h"
 #include "symbol.h"
 #include "tests.h"
···
 	TEST_ASSERT_VAL("No test file", file);
 
 	memset(&machine, 0, sizeof(machine));
+	dsos__init(&machine.dsos);
 
-	dso = dso__new((const char *)file);
-
+	dso = dso__new(file);
+	TEST_ASSERT_VAL("Failed to add dso", !dsos__add(&machine.dsos, dso));
 	TEST_ASSERT_VAL("Failed to access to dso",
 			dso__data_fd(dso, &machine) >= 0);
 
···
 	}
 
 	dso__put(dso);
+	dsos__exit(&machine.dsos);
 	unlink(file);
 	return 0;
 }
···
 	return nr - 1;
 }
 
-static struct dso **dsos;
-
-static int dsos__create(int cnt, int size)
+static int dsos__create(int cnt, int size, struct dsos *dsos)
 {
 	int i;
 
-	dsos = malloc(sizeof(*dsos) * cnt);
-	TEST_ASSERT_VAL("failed to alloc dsos array", dsos);
+	dsos__init(dsos);
 
 	for (i = 0; i < cnt; i++) {
-		char *file;
+		struct dso *dso;
+		char *file = test_file(size);
 
-		file = test_file(size);
 		TEST_ASSERT_VAL("failed to get dso file", file);
-
-		dsos[i] = dso__new(file);
-		TEST_ASSERT_VAL("failed to get dso", dsos[i]);
+		dso = dso__new(file);
+		TEST_ASSERT_VAL("failed to get dso", dso);
+		TEST_ASSERT_VAL("failed to add dso", !dsos__add(dsos, dso));
+		dso__put(dso);
 	}
 
 	return 0;
 }
 
-static void dsos__delete(int cnt)
+static void dsos__delete(struct dsos *dsos)
 {
-	int i;
-
-	for (i = 0; i < cnt; i++) {
-		struct dso *dso = dsos[i];
+	for (unsigned int i = 0; i < dsos->cnt; i++) {
+		struct dso *dso = dsos->dsos[i];
 
 		dso__data_close(dso);
 		unlink(dso__name(dso));
-		dso__put(dso);
 	}
-
-	free(dsos);
+	dsos__exit(dsos);
 }
 
 static int set_fd_limit(int n)
···
 	/* and this is now our dso open FDs limit */
 	dso_cnt = limit / 2;
 	TEST_ASSERT_VAL("failed to create dsos\n",
-		!dsos__create(dso_cnt, TEST_FILE_SIZE));
+			!dsos__create(dso_cnt, TEST_FILE_SIZE, &machine.dsos));
 
 	for (i = 0; i < (dso_cnt - 1); i++) {
-		struct dso *dso = dsos[i];
+		struct dso *dso = machine.dsos.dsos[i];
 
 		/*
 		 * Open dsos via dso__data_fd(), it opens the data
···
 	}
 
 	/* verify the first one is already open */
-	TEST_ASSERT_VAL("dsos[0] is not open", dso__data(dsos[0])->fd != -1);
+	TEST_ASSERT_VAL("dsos[0] is not open", dso__data(machine.dsos.dsos[0])->fd != -1);
 
 	/* open +1 dso to reach the allowed limit */
-	fd = dso__data_fd(dsos[i], &machine);
+	fd = dso__data_fd(machine.dsos.dsos[i], &machine);
 	TEST_ASSERT_VAL("failed to get fd", fd > 0);
 
 	/* should force the first one to be closed */
-	TEST_ASSERT_VAL("failed to close dsos[0]", dso__data(dsos[0])->fd == -1);
+	TEST_ASSERT_VAL("failed to close dsos[0]", dso__data(machine.dsos.dsos[0])->fd == -1);
 
 	/* cleanup everything */
-	dsos__delete(dso_cnt);
+	dsos__delete(&machine.dsos);
 
 	/* Make sure we did not leak any file descriptor. */
 	nr_end = open_files_cnt();
···
 	long nr_end, nr = open_files_cnt(), lim = new_limit(3);
 	int fd, fd_extra;
 
-#define dso_0 (dsos[0])
-#define dso_1 (dsos[1])
-#define dso_2 (dsos[2])
+#define dso_0 (machine.dsos.dsos[0])
+#define dso_1 (machine.dsos.dsos[1])
+#define dso_2 (machine.dsos.dsos[2])
 
 	/* Rest the internal dso open counter limit. */
 	reset_fd_limit();
···
 	TEST_ASSERT_VAL("failed to set file limit",
 			!set_fd_limit((lim)));
 
-	TEST_ASSERT_VAL("failed to create dsos\n", !dsos__create(3, TEST_FILE_SIZE));
+	TEST_ASSERT_VAL("failed to create dsos\n",
+			!dsos__create(3, TEST_FILE_SIZE, &machine.dsos));
 
 	/* open dso_0 */
 	fd = dso__data_fd(dso_0, &machine);
···
 
 	/* cleanup everything */
 	close(fd_extra);
-	dsos__delete(3);
+	dsos__delete(&machine.dsos);
 
 	/* Make sure we did not leak any file descriptor. */
 	nr_end = open_files_cnt();

tools/perf/util/dso.c

···
 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--;
···
 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)
···
 		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;
 }

tools/perf/util/dso.h

···
 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;