From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1C61D431E63; Wed, 1 Jul 2026 20:08:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782936533; cv=none; b=S4dWPtbTlOGcq1M6gqJ7a/rCtjymfn74piUUjjJZRFxYIN1xh68DDYIpRNt0vmTcR31oLdpS31gHS37tQKVXMpu03lYwla/ofRWHsyd2cFJCQ0OIHipum9zi6cmNn0QpT/RO224QJCGKtX5e/ZMXCm6bme849pGKJN6p0ry+RxM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782936533; c=relaxed/simple; bh=h5+MTMur7gUWGAyAmj1dfIFJizEpNBiwAfZLkOsPjZ0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DUU1Zy+DQVc5wxeJegwdcGeXbOB6MBpyoHXrIp4Mbu5Z4Pe/G+jkTX2AiBSqdNKd1RXHeh1vY1rG0OUGfkStx0o4bm5mh9VrkM09nfRlpGEWetBtK935I/kejnbHnTI8Gd8bIMrCy27PXb4fZlSEzCBaIqT8/v0jTNHoYUUVVMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TYaWBAz7; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TYaWBAz7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DAF221F000E9; Wed, 1 Jul 2026 20:08:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782936531; bh=QLxgycIlH73T/Z4NDAOwA1ZnWgwK5lm7yqvdPVfx9jQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=TYaWBAz7dyKXyPdlRA941LMAtZ5+x90gsbHGCk83x7YC2EqtUwrPvBW+nVonPUhcf I4+/mHW6IDsJbblVf6408D6+ybW+HP6IeJ2sdBChiGO3K0fB3Vd/Q1XTCJszQ2vHvp 0RYFQnYWyr7XN9Ndx78idaDl5WygSeeYikUlyRaGjIqvsgy28QZRWhxBvUpGXUh2Bl XHnbWq/ijPBXr5ugw1dhzK59rUTLPt5zOYFSf1lyt8qfXVpY73E45RBPeh/ECe+l4I QQOeM6vzdXbEIwufkvVJwdy8Nu6RLbQJN7efYpOZkFiE64lENYs4T9aYRsx412OEmo ypVS30BDp2elw== Date: Wed, 1 Jul 2026 23:08:45 +0300 From: Mike Rapoport To: Andrew Morton , David Hildenbrand Cc: "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] dev: selftests/mm/uffd: don't treat UFFDIO_COPY -ENOENT as a failure Message-ID: References: <20260701200143.1470229-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260701200143.1470229-1-rppt@kernel.org> Oops, the subject came out wrong, will resend. Sorry for the noise. On Wed, Jul 01, 2026 at 11:01:43PM +0300, Mike Rapoport wrote: > From: "Mike Rapoport (Microsoft)" > > 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) > --- > I've noticed transient faults of uffd-unit-tests in the CI runs [1] > and found this issue with uffd-unit-tests. > > The issue is longstanding and it's not related to or exposed by the > recent uffd refactoring. > > I didn't even look for a Fixes: commit, as this is a selftest only and I > don't see a reason to backport it. > > [1] https://github.com/linux-mm/linux-mm/actions > > 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); > > base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482 > -- > 2.53.0 > -- Sincerely yours, Mike.