On 16/12/2025 15:56, Ryan Roberts wrote:
On 16/12/2025 14:26, Kevin Brodsky wrote:
One of the pagemap_ioctl tests attempts to fault in pages by memcpy()'ing them to an unused buffer. This probably worked originally, but since commit 46036188ea1f ("selftests/mm: build with -O2") the compiler is free to optimise away that unused buffer and the memcpy() with it. As a result there might not be any resident page in the mapping and the test may fail.
We don't need to copy all that memory anyway. Just fault in every page by forcing the compiler to read the first byte.
Cc: Usama Anjum Usama.Anjum@arm.com Signed-off-by: Kevin Brodsky kevin.brodsky@arm.com
tools/testing/selftests/mm/pagemap_ioctl.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/selftests/mm/pagemap_ioctl.c index 2cb5441f29c7..67a7a3705604 100644 --- a/tools/testing/selftests/mm/pagemap_ioctl.c +++ b/tools/testing/selftests/mm/pagemap_ioctl.c @@ -1056,7 +1056,6 @@ int sanity_tests(void) struct page_region *vec; char *mem, *fmem; struct stat sbuf;
- char *tmp_buf;
/* 1. wrong operation */ mem_size = 10 * page_size; @@ -1167,8 +1166,9 @@ int sanity_tests(void) if (fmem == MAP_FAILED) ksft_exit_fail_msg("error nomem %d %s\n", errno, strerror(errno));
- tmp_buf = malloc(sbuf.st_size);
- memcpy(tmp_buf, fmem, sbuf.st_size);
- /* Fault in every page by reading the first byte */
- for (i = 0; i < sbuf.st_size; i += page_size)
(void)*(volatile char *)(fmem + i);We have FORCE_READ() in vm_util.h for this. Perhaps that would be better?
It would, thanks! I wanted to use READ_ONCE() from tools/include/linux/compiler.h but for some reason we don't add tools/include to the include path in the mm kselftests Makefile and I didn't want to dive into that rabbit hole.
- Kevin