[PATCH v4 3/7] selftests/proc: extend /proc/pid/maps tearing test to include vma remapping

[Suren Baghdasaryan <surenb@google.com>]

Test that /proc/pid/maps does not report unexpected holes in the address
space when we concurrently remap a part of a vma into the middle of
another vma. This remapping results in the destination vma being split
into three parts and the part in the middle being patched back from,
all done concurrently from under the reader. We should always see either
original vma or the split one with no holes.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 tools/testing/selftests/proc/proc-pid-vm.c | 92 ++++++++++++++++++++++
 1 file changed, 92 insertions(+)

diff --git a/tools/testing/selftests/proc/proc-pid-vm.c b/tools/testing/selftests/proc/proc-pid-vm.c
index 39842e4ec45f..1aef2db7e893 100644
--- a/tools/testing/selftests/proc/proc-pid-vm.c
+++ b/tools/testing/selftests/proc/proc-pid-vm.c
@@ -663,6 +663,95 @@ static void test_maps_tearing_from_resize(int maps_fd,
 	signal_state(mod_info, TEST_DONE);
 }
 
+static inline void remap_vma(const struct vma_modifier_info *mod_info)
+{
+	/*
+	 * Remap the last page of the next vma into the middle of the vma.
+	 * This splits the current vma and the first and middle parts (the
+	 * parts at lower addresses) become the last vma objserved in the
+	 * first page and the first vma observed in the last page.
+	 */
+	assert(mremap(mod_info->next_addr + page_size * 2, page_size,
+		      page_size, MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+		      mod_info->addr + page_size) != MAP_FAILED);
+}
+
+static inline void patch_vma(const struct vma_modifier_info *mod_info)
+{
+	assert(!mprotect(mod_info->addr + page_size, page_size,
+			 mod_info->prot));
+}
+
+static inline void check_remap_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 vmas at the boundaries are changing */
+	assert(strcmp(mod_last_line->text, restored_last_line->text) != 0);
+	assert(strcmp(mod_first_line->text, restored_first_line->text) != 0);
+}
+
+static void test_maps_tearing_from_remap(int maps_fd,
+				struct vma_modifier_info *mod_info,
+				struct page_content *page1,
+				struct page_content *page2,
+				struct line_content *last_line,
+				struct line_content *first_line)
+{
+	struct line_content remapped_last_line;
+	struct line_content remapped_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 */
+	read_boundary_lines(maps_fd, page1, page2, last_line, first_line);
+
+	mod_info->vma_modify = remap_vma;
+	mod_info->vma_restore = patch_vma;
+	mod_info->vma_mod_check = check_remap_result;
+
+	capture_mod_pattern(maps_fd, mod_info, page1, page2, last_line, first_line,
+			    &remapped_last_line, &remapped_first_line,
+			    &restored_last_line, &restored_first_line);
+
+	/* Now start concurrent modifications for test_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 {
+		read_boundary_lines(maps_fd, page1, page2, &new_last_line, &new_first_line);
+
+		/* Check if we read vmas after remapping it */
+		if (!strcmp(new_last_line.text, remapped_last_line.text)) {
+			/*
+			 * The vmas should be consistent with remap results,
+			 * however if the vma was concurrently restored, it
+			 * can be reported twice (first as split 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(!strcmp(new_first_line.text, remapped_first_line.text) ||
+			       !strcmp(new_first_line.text, restored_last_line.text));
+		} else {
+			/* The vmas should be consistent with the original/resored state */
+			assert(!strcmp(new_last_line.text, restored_last_line.text) &&
+			       !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 < test_duration_sec);
+
+	/* Signal the modifyer thread to stop and wait until it exits */
+	signal_state(mod_info, TEST_DONE);
+}
+
 static int test_maps_tearing(void)
 {
 	struct vma_modifier_info *mod_info;
@@ -757,6 +846,9 @@ static int test_maps_tearing(void)
 	test_maps_tearing_from_resize(maps_fd, mod_info, &page1, &page2,
 				      &last_line, &first_line);
 
+	test_maps_tearing_from_remap(maps_fd, mod_info, &page1, &page2,
+				     &last_line, &first_line);
+
 	stop_vma_modifier(mod_info);
 
 	free(page2.data);
-- 
2.49.0.1266.g31b7d2e469-goog