From 5491b25d4ae99a59cada18aa03e0ac838b5fd725 Mon Sep 17 00:00:00 2001 From: "Mike Rapoport (Microsoft)" Date: Wed, 1 Jul 2026 23:09:32 +0300 Subject: [PATCH] selftests/mm/uffd: don't treat UFFDIO_COPY -ENOENT as a failure Non-cooperarive uffd events are inherently racy and can happen in parallel with other userfaultfd operations. During event tests in uffd-unit-tests, the uffd monitor calls UFFDIO_UNREGISTER upon receiving UFFD_EVENT_REMOVE. In parallel, the faulting_process() verifies that the removed memory is actually zeroed. If a verification read wins the race with UFFDIO_UNREGISTER, it causes a missing fault that uffd monitor would receive after UFFDIO_UNREGISTER is complete. The monitor resolves the fault using UFFDIO_COPY that fails with -ENOENT which means that VMA has been changed (see commit 27d02568f529 ("userfaultfd: mcopy_atomic: return -ENOENT when no compatible VMA found")). Treat -ENOENT returned by UFFDIO_COPY as non-fatal, the same way -EEXIST is treated for concurrent faults, and don't fail the test. Link: https://lore.kernel.org/20260701200932.1470525-1-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) Reviewed-by: Lorenzo Stoakes Reviewed-by: David Hildenbrand (Arm) Cc: Liam R. Howlett Cc: Michal Hocko Cc: Peter Xu Cc: Shuah Khan Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- tools/testing/selftests/mm/uffd-common.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c index edd02328f77b..f48f5d4594ab 100644 --- a/tools/testing/selftests/mm/uffd-common.c +++ b/tools/testing/selftests/mm/uffd-common.c @@ -639,8 +639,13 @@ int __copy_page(uffd_global_test_opts_t *gopts, unsigned long offset, bool retry uffdio_copy.mode = 0; uffdio_copy.copy = 0; if (ioctl(gopts->uffd, UFFDIO_COPY, &uffdio_copy)) { - /* real retval in ufdio_copy.copy */ - if (uffdio_copy.copy != -EEXIST) + /* + * real retval in uffdio_copy.copy + * + * -EEXIST: the page was faulted in concurrently + * -ENOENT: the destination range was concurrently removed + */ + if (uffdio_copy.copy != -EEXIST && uffdio_copy.copy != -ENOENT) err("UFFDIO_COPY error: %"PRId64, (int64_t)uffdio_copy.copy); wake_range(gopts->uffd, uffdio_copy.dst, gopts->page_size);