[merged mm-stable] selftests-mm-uffd-dont-treat-uffdio_copy-enoent-as-a-failure.patch removed from -mm tree

[merged mm-stable] selftests-mm-uffd-dont-treat-uffdio_copy-enoent-as-a-failure.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: selftests/mm/uffd: don't treat UFFDIO_COPY -ENOENT as a failure
has been removed from the -mm tree.  Its filename was
     selftests-mm-uffd-dont-treat-uffdio_copy-enoent-as-a-failure.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Subject: selftests/mm/uffd: don't treat UFFDIO_COPY -ENOENT as a failure
Date: Wed, 1 Jul 2026 23:09:32 +0300

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) <rppt@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/uffd-common.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/mm/uffd-common.c~selftests-mm-uffd-dont-treat-uffdio_copy-enoent-as-a-failure
+++ a/tools/testing/selftests/mm/uffd-common.c
@@ -639,8 +639,13 @@ int __copy_page(uffd_global_test_opts_t
 		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);
_

Patches currently in -mm which might be from rppt@kernel.org are

mm-split-out-mm_init-and-memblock-declarations-from-internalh.patch
mm-split-out-mm_init-and-memblock-declarations-from-internalh-fix.patch
mm-split-out-sparse-declarations-from-internalh.patch
mm-split-out-vmalloc-declarations-from-internalh.patch