linux-kernel - [PATCH v3 2/8] selftests/proc: extend /proc/pid/maps tearing test to include vma resizing

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Message-ID: <20250418174959.1431962-3-surenb@google.com>
Date: Fri, 18 Apr 2025 10:49:53 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, david@...hat.com, 
	vbabka@...e.cz, peterx@...hat.com, jannh@...gle.com, hannes@...xchg.org, 
	mhocko@...nel.org, paulmck@...nel.org, shuah@...nel.org, adobriyan@...il.com, 
	brauner@...nel.org, josef@...icpanda.com, yebin10@...wei.com, 
	linux@...ssschuh.net, willy@...radead.org, osalvador@...e.de, 
	andrii@...nel.org, ryan.roberts@....com, christophe.leroy@...roup.eu, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-mm@...ck.org, linux-kselftest@...r.kernel.org, surenb@...gle.com
Subject: [PATCH v3 2/8] selftests/proc: extend /proc/pid/maps tearing test to
 include vma resizing

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@...gle.com>
---
 tools/testing/selftests/proc/proc-pid-vm.c | 83 ++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/tools/testing/selftests/proc/proc-pid-vm.c b/tools/testing/selftests/proc/proc-pid-vm.c
index 6e3f06376a1f..39842e4ec45f 100644
--- a/tools/testing/selftests/proc/proc-pid-vm.c
+++ b/tools/testing/selftests/proc/proc-pid-vm.c
@@ -583,6 +583,86 @@ static void test_maps_tearing_from_split(int maps_fd,
 	signal_state(mod_info, TEST_DONE);
 }
 
+static inline void shrink_vma(const struct vma_modifier_info *mod_info)
+{
+	assert(mremap(mod_info->addr, page_size * 3, page_size, 0) != MAP_FAILED);
+}
+
+static inline void expand_vma(const struct vma_modifier_info *mod_info)
+{
+	assert(mremap(mod_info->addr, page_size, page_size * 3, 0) != MAP_FAILED);
+}
+
+static inline void 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 */
+	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_resize(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 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 */
+	read_boundary_lines(maps_fd, page1, page2, last_line, first_line);
+
+	mod_info->vma_modify = shrink_vma;
+	mod_info->vma_restore = expand_vma;
+	mod_info->vma_mod_check = check_shrink_result;
+
+	capture_mod_pattern(maps_fd, mod_info, page1, page2, last_line, first_line,
+			    &shrunk_last_line, &shrunk_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 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(!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(!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;
@@ -674,6 +754,9 @@ static int test_maps_tearing(void)
 	test_maps_tearing_from_split(maps_fd, mod_info, &page1, &page2,
 				     &last_line, &first_line);
 
+	test_maps_tearing_from_resize(maps_fd, mod_info, &page1, &page2,
+				      &last_line, &first_line);
+
 	stop_vma_modifier(mod_info);
 
 	free(page2.data);
-- 
2.49.0.805.g082f7c87e0-goog