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

This test verifies that a hugepage, used as a user buffer for DIO
operations, is correctly freed upon unmapping.  To test this, we read the
count of free hugepages before and after the mmap, DIO, and munmap
operations, then check if the free hugepage count is the same.

Reading free hugepages before the test was removed by commit 0268d457
('selftests: hugetlb_dio: check for initial conditions to skip at the
start'), causing the test to always fail.

This patch adds back reading the free hugepages before starting the test. 
With this patch, the tests are now passing.

Test results without this patch:

./tools/testing/selftests/mm/hugetlb_dio
TAP version 13
1..4
 # No. Free pages before allocation : 0
 # No. Free pages after munmap : 100
not ok 1 : Huge pages not freed!
 # No. Free pages before allocation : 0
 # No. Free pages after munmap : 100
not ok 2 : Huge pages not freed!
 # No. Free pages before allocation : 0
 # No. Free pages after munmap : 100
not ok 3 : Huge pages not freed!
 # No. Free pages before allocation : 0
 # No. Free pages after munmap : 100
not ok 4 : Huge pages not freed!
 # Totals: pass:0 fail:4 xfail:0 xpass:0 skip:0 error:0

Test results with this patch:

/tools/testing/selftests/mm/hugetlb_dio
TAP version 13
1..4
# No. Free pages before allocation : 100
# No. Free pages after munmap : 100
ok 1 : Huge pages freed successfully !
# No. Free pages before allocation : 100
# No. Free pages after munmap : 100
ok 2 : Huge pages freed successfully !
# No. Free pages before allocation : 100
# No. Free pages after munmap : 100
ok 3 : Huge pages freed successfully !
# No. Free pages before allocation : 100
# No. Free pages after munmap : 100
ok 4 : Huge pages freed successfully !

# Totals: pass:4 fail:0 xfail:0 xpass:0 skip:0 error:0

Link: https://lkml.kernel.org/r/20241110064903.23626-1-donettom@linux.ibm.com


Fixes: 0268d457 ("selftests: hugetlb_dio: check for initial conditions to skip in the start")
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>