The error handling in hugetlb_allocate_area() was incorrect for the hugetlb_shared test case.

Previously the behavior was:

- mmap a hugetlb area - If this fails, set the pointer to NULL, and carry on - mmap an alias of the same hugetlb fd - If this fails, munmap the original area

If the original mmap failed, it's likely the second one did too. If both failed, we'd blindly try to munmap a NULL pointer, causing a SIGSEGV. Instead, "goto fail" so we return before trying to mmap the alias.

This issue can be hit "in real life" by forgetting to set /proc/sys/vm/nr_hugepages (leaving it at 0), and then trying to run the hugetlb_shared test.

Another small improvement is, when the original mmap fails, don't just print "it failed": perror(), so we can see *why*. :)

Signed-off-by: Axel Rasmussen axelrasmussen@google.com --- tools/testing/selftests/vm/userfaultfd.c | 25 +++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c index 9b0912a01777..c4425597769a 100644 --- a/tools/testing/selftests/vm/userfaultfd.c +++ b/tools/testing/selftests/vm/userfaultfd.c @@ -206,19 +206,19 @@ static int hugetlb_release_pages(char *rel_area) return ret; }

- static void hugetlb_allocate_area(void **alloc_area) { void *area_alias = NULL; char **alloc_area_alias; + *alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE, (map_shared ? MAP_SHARED : MAP_PRIVATE) | MAP_HUGETLB, huge_fd, *alloc_area == area_src ? 0 : nr_pages * page_size); if (*alloc_area == MAP_FAILED) { - fprintf(stderr, "mmap of hugetlbfs file failed\n"); - *alloc_area = NULL; + perror("mmap of hugetlbfs file failed"); + goto fail; }

if (map_shared) { @@ -227,14 +227,11 @@ static void hugetlb_allocate_area(void **alloc_area) huge_fd, *alloc_area == area_src ? 0 : nr_pages * page_size); if (area_alias == MAP_FAILED) { - if (munmap(*alloc_area, nr_pages * page_size) < 0) { - perror("hugetlb munmap"); - exit(1); - } - *alloc_area = NULL; - return; + perror("mmap of hugetlb file alias failed"); + goto fail_munmap; } } + if (*alloc_area == area_src) { huge_fd_off0 = *alloc_area; alloc_area_alias = &area_src_alias; @@ -243,6 +240,16 @@ static void hugetlb_allocate_area(void **alloc_area) } if (area_alias) *alloc_area_alias = area_alias; + + return; + +fail_munmap: + if (munmap(*alloc_area, nr_pages * page_size) < 0) { + perror("hugetlb munmap"); + exit(1); + } +fail: + *alloc_area = NULL; }

static void hugetlb_alias_mapping(__u64 *start, size_t len, unsigned long offset)