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Subject: Re: [PATCH 1/3] mm/hugetlb: Fix race condition of uffd missing/minor
 handling
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <YztRR35U6gI/CA4r@x1n>
Date:   Mon, 3 Oct 2022 14:32:31 -0700
Cc:     LKML <linux-kernel@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mike Kravetz <mike.kravetz@oracle.com>
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Message-Id: <568C0BF2-28B9-438C-93D2-19130FAA3364@gmail.com>
References: <20221003155630.469263-1-peterx@redhat.com>
 <20221003155630.469263-2-peterx@redhat.com>
 <BBCFE41B-9ABB-49C1-BDC7-EAF07964A6FF@gmail.com> <YztRR35U6gI/CA4r@x1n>
To:     Peter Xu <peterx@redhat.com>
Precedence: bulk

On Oct 3, 2022, at 2:16 PM, Peter Xu <peterx@redhat.com> wrote:

> On Mon, Oct 03, 2022 at 02:00:36PM -0700, Nadav Amit wrote:
>> On Oct 3, 2022, at 8:56 AM, Peter Xu <peterx@redhat.com> wrote:
>>=20
>>> +			 */
>>> +			if (hugetlb_pte_stable(h, mm, ptep, old_pte))
>>> +				ret =3D hugetlb_handle_userfault(
>>> +				    vma, mapping, idx, flags, haddr,
>>> +				    address, VM_UFFD_MISSING);
>>> +			else
>>> +				/* Retry the fault */
>>> +				ret =3D 0;
>>=20
>> Might be unrelated, but at least for the sake of consistency if not
>> potential GUP issues, don=E2=80=99t you want to return VM_FAULT_RETRY =
?
>=20
> VM_FAULT_RETRY implies releasing of mmap sem, while we didn't?

Of course. My bad.