From: Andrew Morton <akpm@linux-foundation.org>
To: Mina Almasry <almasrymina@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>,
Peter Xu <peterx@redhat.com>,
linux-mm@kvack.org, Mike Kravetz <mike.kravetz@oracle.com>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY
Date: Mon, 31 May 2021 17:37:33 -0700 [thread overview]
Message-ID: <20210531173733.615fd539396ff7a173a2bf8b@linux-foundation.org> (raw)
In-Reply-To: <20210528004649.85298-1-almasrymina@google.com>
On Thu, 27 May 2021 17:46:49 -0700 Mina Almasry <almasrymina@google.com> wrote:
> The userfaultfd hugetlb tests detect a resv_huge_pages underflow. This
> happens when hugetlb_mcopy_atomic_pte() is called with !is_continue on
> an index for which we already have a page in the cache. When this
> happens, we allocate a second page, double consuming the reservation,
> and then fail to insert the page into the cache and return -EEXIST.
>
> To fix this, we first if there exists a page in the cache which already
> consumed the reservation, and return -EEXIST immediately if so.
>
> There is still a rare condition where we fail to copy the page contents
> AND race with a call for hugetlb_no_page() for this index and again we
> will underflow resv_huge_pages. That is fixed in a more complicated
> patch not targeted for -stable.
>
> Test:
> Hacked the code locally such that resv_huge_pages underflows produce
> a warning, then:
>
> ./tools/testing/selftests/vm/userfaultfd hugetlb_shared 10
> 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success
> ./tools/testing/selftests/vm/userfaultfd hugetlb 10
> 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success
>
> Both tests succeed and produce no warnings. After the
> test runs number of free/resv hugepages is correct.
>
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> Cc: Axel Rasmussen <axelrasmussen@google.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: linux-mm@kvack.org
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Cc: stable@vger.kernel.org
Do we have a Fixes: for this, or is it an always-been-there issue?
next prev parent reply other threads:[~2021-06-01 0:37 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-28 0:46 [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY Mina Almasry
2021-05-28 18:43 ` Mike Kravetz
2021-06-01 0:37 ` Andrew Morton [this message]
2021-06-01 2:49 ` Mina Almasry
2021-06-01 16:59 ` Mike Kravetz
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