Add mincore() test for pages cached by another process

It tests the result of mincore when memory is mapped and cached by
another process. A file is mapped in both parent and child
process.Then the mapped memory is accessed in the child process. The
results of mincore are tested in the parent process.

Closes: #460

Signed-off-by: Shwetha Subramanian. <shwetha@zilogic.com>
Reviewed-by: Vijay Kumar B. <vijaykumar@zilogic.com>
Acked-by: Jan Stancek <jstancek@redhat.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>

runtest/syscalls

@@ -879,6 +879,7 @@ open_tree02 open_tree02
 mincore01 mincore01
 mincore02 mincore02
 mincore03 mincore03
+mincore04 mincore04
 
 madvise01 madvise01
 madvise02 madvise02

testcases/kernel/syscalls/mincore/.gitignore

@@ -1,3 +1,4 @@
 /mincore01
 /mincore02
 /mincore03
+/mincore04

testcases/kernel/syscalls/mincore/mincore04.c

@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) Zilogic Systems Pvt. Ltd., 2020
+ * Email: code@zilogic.com
+ */
+
+/*
+ * mincore04
+ * Test shows that pages mapped in one process(parent) and
+ * faulted in another(child) results in mincore(in parent) reporting
+ * that all mapped pages are resident.
+ */
+
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include "tst_test.h"
+
+#define NUM_PAGES 3
+
+static int fd;
+static int size;
+static void *ptr;
+
+static void cleanup(void)
+{
+	if (fd > 0)
+		SAFE_CLOSE(fd);
+	if (ptr) {
+		SAFE_MUNLOCK(ptr, size);
+		SAFE_MUNMAP(ptr, size);
+	}
+}
+
+static void setup(void)
+{
+	int page_size, ret;
+
+	page_size = getpagesize();
+	size = page_size * NUM_PAGES;
+	fd = SAFE_OPEN("FILE", O_CREAT | O_RDWR, 0600);
+	SAFE_FTRUNCATE(fd, size);
+
+	/* File pages from file creation are cleared from cache. */
+	SAFE_FSYNC(fd);
+	ret = posix_fadvise(fd, 0, size, POSIX_FADV_DONTNEED);
+	if (ret == -1)
+		tst_brk(TBROK | TERRNO, "fadvise failed");
+}
+
+static void lock_file(void)
+{
+	SAFE_MLOCK(ptr, size);
+	TST_CHECKPOINT_WAKE(0);
+	TST_CHECKPOINT_WAIT(1);
+}
+
+static int count_pages_in_cache(void)
+{
+	int locked_pages = 0;
+	int count, ret;
+	unsigned char vec[NUM_PAGES];
+
+	TST_CHECKPOINT_WAIT(0);
+
+	ret = mincore(ptr, size, vec);
+	if (ret == -1)
+		tst_brk(TBROK | TERRNO, "mincore failed");
+	for (count = 0; count < NUM_PAGES; count++) {
+		if (vec[count] & 1)
+			locked_pages++;
+	}
+
+	TST_CHECKPOINT_WAKE(1);
+	return locked_pages;
+}
+
+static void test_mincore(void)
+{
+	int  locked_pages;
+
+	ptr = SAFE_MMAP(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	pid_t child_pid = SAFE_FORK();
+
+	if (child_pid == 0) {
+		lock_file();
+		exit(0);
+	}
+
+	locked_pages = count_pages_in_cache();
+	tst_reap_children();
+
+	if (locked_pages == NUM_PAGES)
+		tst_res(TPASS, "mincore reports all %d pages locked by child process "
+			"are resident", locked_pages);
+	else
+		tst_res(TFAIL, "mincore reports %d pages resident but %d pages "
+			"locked by child process", locked_pages, NUM_PAGES);
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.cleanup = cleanup,
+	.forks_child = 1,
+	.test_all = test_mincore,
+	.needs_checkpoints = 1,
+};