[LTP] [PATCH] hugemmap24: increase the baseline of slice_boundary according to hpage size

[Li Wang]

This is to avoid error happens on system (aarch64: 512MB) with large huge page:

  # ./hugemmap24
  tst_hugepage.c:83: TINFO: 7 hugepage(s) reserved
  tst_test.c:1560: TINFO: Timeout per run is 0h 00m 30s
  hugemmap24.c:57: TINFO: can't use slice_boundary: 0x10000000: EINVAL (22)
  hugemmap24.c:57: TINFO: can't use slice_boundary: 0x20000000: ENOMEM (12)
  hugemmap24.c:57: TINFO: can't use slice_boundary: 0x30000000: EINVAL (22)
  tst_test.c:1618: TBROK: Test killed by SIGSEGV!

  # strace -f ./hugemmap24：
  ...
  [pid 86580] mmap(0xfffffffff0000000, 2147483648, PROT_READ, MAP_SHARED|MAP_FIXED, 3, 0) = -1 EINVAL
  [pid 86580] write(2, "hugemmap24.c:57: \33[1;34mTINFO: \33"..., 85hugemmap24.c:57: TINFO: can't use slice_boundary: 0x30000000: EINVAL (22)) = 85
  [pid 86580] mmap(NULL, 2147483648, PROT_READ, MAP_SHARED|MAP_FIXED, 3, 0) = 0
  [pid 86580] --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_ACCERR, si_addr=0x404338} ---
  [pid 86580] +++ killed by SIGSEGV (core dumped) +++

  # cat /proc/meminfo
  Hugepagesize: 524288 kB

Note:
  This is basically an improved patch based on Jan's work, the only
  difference is that to bypass the heap and avoid some potential
  mmap collisions.

  Patch get passed on RHEL-7/8/9 across many arches.
  (x86_64, ppc64le, ppc64, aarch64, s390x)

Closes: https://github.com/linux-test-project/ltp/issues/1022
Discuss: https://lists.linux.it/pipermail/ltp/2023-March/033117.html

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Jan Stancek <jstancek@redhat.com>
Cc: Tarun Sahu <tsahu@linux.ibm.com>
Cc: Fanhui Meng <mengfanhui@kylinos.cn>
---
 testcases/kernel/mem/hugetlb/hugemmap/hugemmap24.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap24.c b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap24.c
index a465aadec..158a03010 100644
--- a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap24.c
+++ b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap24.c
@@ -23,7 +23,7 @@
 
 static int  fd = -1;
 static unsigned long slice_boundary;
-static long hpage_size, page_size;
+static unsigned long hpage_size, page_size;
 
 static int init_slice_boundary(int fd)
 {
@@ -44,6 +44,13 @@ static int init_slice_boundary(int fd)
 	heap = malloc(1);
 	free(heap);
 
+	 /* Avoid underflow on systems with large huge pages.
+	  * The additionally plus heap address is to reduce the possibility
+	  * of MAP_FIXED stomp over existing mappings.
+	  */
+	while (slice_boundary + slice_size < (unsigned long)heap + 2*hpage_size)
+		slice_boundary += slice_size;
+
 	/* Find 2 neighbour slices with couple huge pages free
 	 * around slice boundary.
 	 * 16 is the maximum number of slices (low/high)
-- 
2.40.0