[PATCH v2] selftests/proc: Add test to check unmapped process

[Siddharth Menon <simeddon@gmail.com>]

Introduce test 'test_proc_pid_mem' to address the issue in the TODO.
Check if VMsize is 0 to determine whether the process has been unmapped.
The child process cannot signal the parent that it has unmapped itself,
as it no longer exists. This includes unmapping the text segment,
preventing the child from proceeding to the next instruction.

Signed-off-by: Siddharth Menon <simeddon@gmail.com>
---
 v1->v2: Removed redundant parenthesis, fixed other checkpatch warnings.
 Revised commit message based on feedback.
 
 tools/testing/selftests/proc/proc-empty-vm.c | 56 +++++++++++++++++---
 1 file changed, 50 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/proc/proc-empty-vm.c b/tools/testing/selftests/proc/proc-empty-vm.c
index b3f898aab4ab..bfb7f8823529 100644
--- a/tools/testing/selftests/proc/proc-empty-vm.c
+++ b/tools/testing/selftests/proc/proc-empty-vm.c
@@ -213,6 +213,53 @@ static void vsyscall(void)
 }
 #endif
 
+static int test_proc_pid_mem(pid_t pid)
+{
+	char buf[4096];
+	char *line;
+	int vm_size = -1;
+
+	snprintf(buf, sizeof(buf), "/proc/%d/status", pid);
+	int fd = open(buf, O_RDONLY);
+
+	if (fd == -1) {
+		if (errno == ENOENT)
+			/* Process does not exist */
+			return EXIT_SUCCESS;
+
+	perror("open /proc/[pid]/status");
+	return EXIT_FAILURE;
+	}
+
+	ssize_t rv = read(fd, buf, sizeof(buf) - 1);
+
+	if (rv == -1) {
+		perror("read");
+		close(fd);
+		return EXIT_FAILURE;
+	}
+	buf[rv] = '\0';
+
+	line = strtok(buf, "\n");
+	while (line != NULL) {
+		/* Check for VmSize */
+		if (strncmp(line, "VmSize:", 7) == 0) {
+			if (sscanf(line, "VmSize: %d", &vm_size) == 1)
+				break;
+			perror("Failed to parse VmSize.\n");
+		}
+		line = strtok(NULL, "\n");
+	}
+
+	close(fd);
+
+	/* Check if VmSize is 0 */
+	if (vm_size == 0)
+		return EXIT_SUCCESS;
+
+	return EXIT_FAILURE;
+}
+
 static int test_proc_pid_maps(pid_t pid)
 {
 	char buf[4096];
@@ -500,14 +547,11 @@ int main(void)
 #endif
 		return EXIT_FAILURE;
 	} else {
-		/*
-		 * TODO find reliable way to signal parent that munmap(2) completed.
-		 * Child can't do it directly because it effectively doesn't exist
-		 * anymore. Looking at child's VM files isn't 100% reliable either:
-		 * due to a bug they may not become empty or empty-like.
-		 */
 		sleep(1);
 
+		if (rv == EXIT_SUCCESS)
+			rv = test_proc_pid_mem(pid);
+
 		if (rv == EXIT_SUCCESS) {
 			rv = test_proc_pid_maps(pid);
 		}
-- 
2.39.5