Re: [PATCH RESEND] selftests/mm/uffd: don't treat UFFDIO_COPY -ENOENT as a failure

[David Hildenbrand (Arm)]

On 7/1/26 22:09, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>
> 
> 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.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> ---

Reviewed-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David