selftests: hugetlb_dio: check for initial conditions to skip in the start

commit 0268d45 upstream.

The test should be skipped if initial conditions aren't fulfilled in the
start instead of failing and outputting non-compliant TAP logs.  This kind
of failure pollutes the results.  The initial conditions are:

- The test should only execute if /tmp file can be allocated.
- The test should only execute if huge pages are free.

Before:
TAP version 13
1..4
Bail out! Error opening file
: Read-only file system (30)
 # Planned tests != run tests (4 != 0)
 # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0

After:
TAP version 13
1..0 # SKIP Unable to allocate file: Read-only file system

Link: https://lkml.kernel.org/r/20241101141557.3159432-1-usama.anjum@collabora.com
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Fixes: 3a103b5 ("selftest: mm: Test if hugepage does not get leaked during __bio_release_pages()")
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Donet Tom <donettom@linux.ibm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Muhammad Usama Anjum

tools/testing/selftests/mm/hugetlb_dio.c

@@ -44,13 +44,6 @@ void run_dio_using_hugetlb(unsigned int start_off, unsigned int end_off)
 	if (fd < 0)
 		ksft_exit_fail_perror("Error opening file\n");
 
-	/* Get the free huge pages before allocation */
-	free_hpage_b = get_free_hugepages();
-	if (free_hpage_b == 0) {
-		close(fd);
-		ksft_exit_skip("No free hugepage, exiting!\n");
-	}
-
 	/* Allocate a hugetlb page */
 	orig_buffer = mmap(NULL, h_pagesize, mmap_prot, mmap_flags, -1, 0);
 	if (orig_buffer == MAP_FAILED) {
@@ -94,8 +87,20 @@ void run_dio_using_hugetlb(unsigned int start_off, unsigned int end_off)
 int main(void)
 {
 	size_t pagesize = 0;
+	int fd;
 
 	ksft_print_header();
+
+	/* Open the file to DIO */
+	fd = open("/tmp", O_TMPFILE | O_RDWR | O_DIRECT, 0664);
+	if (fd < 0)
+		ksft_exit_skip("Unable to allocate file: %s\n", strerror(errno));
+	close(fd);
+
+	/* Check if huge pages are free */
+	if (!get_free_hugepages())
+		ksft_exit_skip("No free hugepage, exiting\n");
+
 	ksft_set_plan(4);
 
 	/* Get base page size */