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selftests/mm/uffd: don't treat UFFDIO_COPY -ENOENT as a failure

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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
27d02568f5 ("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>
This commit is contained in:
Mike Rapoport (Microsoft) 2026-07-01 23:09:32 +03:00 committed by Andrew Morton
parent 6a8024511d
commit 5491b25d4a
1 changed files with 7 additions and 2 deletions
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9
tools/testing/selftests/mm/uffd-common.c
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@ -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);