From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Mike Rapoport <rppt@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: "Liam R. Howlett" <liam@infradead.org>,
Lorenzo Stoakes <ljs@kernel.org>, Michal Hocko <mhocko@suse.com>,
Peter Xu <peterx@redhat.com>, Shuah Khan <shuah@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Vlastimil Babka <vbabka@kernel.org>,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH RESEND] selftests/mm/uffd: don't treat UFFDIO_COPY -ENOENT as a failure
Date: Thu, 2 Jul 2026 10:03:15 +0200 [thread overview]
Message-ID: <fc2d81a2-0bce-418d-ad0b-fa3856514781@kernel.org> (raw)
In-Reply-To: <20260701200932.1470525-1-rppt@kernel.org>
On 7/1/26 22:09, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>
> 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@kernel.org>
> ---
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
--
Cheers,
David
next prev parent reply other threads:[~2026-07-02 8:03 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-01 20:09 [PATCH RESEND] selftests/mm/uffd: don't treat UFFDIO_COPY -ENOENT as a failure Mike Rapoport
2026-07-02 8:03 ` David Hildenbrand (Arm) [this message]
2026-07-02 10:33 ` Lorenzo Stoakes
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