[PATCH v8 2/6] selftests/proc: extend /proc/pid/maps tearing test to include vma resizing

[Suren Baghdasaryan <surenb@google.com>]

Test that /proc/pid/maps does not report unexpected holes in the address
space when a vma at the edge of the page is being concurrently remapped.
This remapping results in the vma shrinking and expanding from  under the
reader. We should always see either shrunk or expanded (original) version
of the vma.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 tools/testing/selftests/proc/proc-maps-race.c | 79 +++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/tools/testing/selftests/proc/proc-maps-race.c b/tools/testing/selftests/proc/proc-maps-race.c
index 5b28dda08b7d..19028bd3b85c 100644
--- a/tools/testing/selftests/proc/proc-maps-race.c
+++ b/tools/testing/selftests/proc/proc-maps-race.c
@@ -242,6 +242,28 @@ static inline bool check_split_result(struct line_content *mod_last_line,
 	       strcmp(mod_first_line->text, restored_first_line->text) != 0;
 }
 
+static inline bool shrink_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+	return mremap(self->mod_info->addr, self->page_size * 3,
+		      self->page_size, 0) != MAP_FAILED;
+}
+
+static inline bool expand_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+	return mremap(self->mod_info->addr, self->page_size,
+		      self->page_size * 3, 0) != MAP_FAILED;
+}
+
+static inline bool check_shrink_result(struct line_content *mod_last_line,
+				       struct line_content *mod_first_line,
+				       struct line_content *restored_last_line,
+				       struct line_content *restored_first_line)
+{
+	/* Make sure only the last vma of the first page is changing */
+	return strcmp(mod_last_line->text, restored_last_line->text) != 0 &&
+	       strcmp(mod_first_line->text, restored_first_line->text) == 0;
+}
+
 FIXTURE_SETUP(proc_maps_race)
 {
 	const char *duration = getenv("DURATION");
@@ -444,4 +466,61 @@ TEST_F(proc_maps_race, test_maps_tearing_from_split)
 	signal_state(mod_info, TEST_DONE);
 }
 
+TEST_F(proc_maps_race, test_maps_tearing_from_resize)
+{
+	struct vma_modifier_info *mod_info = self->mod_info;
+
+	struct line_content shrunk_last_line;
+	struct line_content shrunk_first_line;
+	struct line_content restored_last_line;
+	struct line_content restored_first_line;
+
+	wait_for_state(mod_info, SETUP_READY);
+
+	/* re-read the file to avoid using stale data from previous test */
+	ASSERT_TRUE(read_boundary_lines(self, &self->last_line, &self->first_line));
+
+	mod_info->vma_modify = shrink_vma;
+	mod_info->vma_restore = expand_vma;
+	mod_info->vma_mod_check = check_shrink_result;
+
+	ASSERT_TRUE(capture_mod_pattern(self, &shrunk_last_line, &shrunk_first_line,
+					&restored_last_line, &restored_first_line));
+
+	/* Now start concurrent modifications for self->duration_sec */
+	signal_state(mod_info, TEST_READY);
+
+	struct line_content new_last_line;
+	struct line_content new_first_line;
+	struct timespec start_ts, end_ts;
+
+	clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts);
+	do {
+		ASSERT_TRUE(read_boundary_lines(self, &new_last_line, &new_first_line));
+
+		/* Check if we read vmas after shrinking it */
+		if (!strcmp(new_last_line.text, shrunk_last_line.text)) {
+			/*
+			 * The vmas should be consistent with shrunk results,
+			 * however if the vma was concurrently restored, it
+			 * can be reported twice (first as shrunk one, then
+			 * as restored one) because we found it as the next vma
+			 * again. In that case new first line will be the same
+			 * as the last restored line.
+			 */
+			ASSERT_FALSE(strcmp(new_first_line.text, shrunk_first_line.text) &&
+				     strcmp(new_first_line.text, restored_last_line.text));
+		} else {
+			/* The vmas should be consistent with the original/resored state */
+			ASSERT_FALSE(strcmp(new_last_line.text, restored_last_line.text));
+			ASSERT_FALSE(strcmp(new_first_line.text, restored_first_line.text));
+		}
+
+		clock_gettime(CLOCK_MONOTONIC_COARSE, &end_ts);
+	} while (end_ts.tv_sec - start_ts.tv_sec < self->duration_sec);
+
+	/* Signal the modifyer thread to stop and wait until it exits */
+	signal_state(mod_info, TEST_DONE);
+}
+
 TEST_HARNESS_MAIN
-- 
2.50.0.727.gbf7dc18ff4-goog