linux-kernel - Re: [PATCH 1/3] mm/hugetlb: Fix race condition of uffd missing/minor handling

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Date:   Mon, 3 Oct 2022 17:16:55 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH 1/3] mm/hugetlb: Fix race condition of uffd missing/minor
 handling

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

VM_FAULT_RETRY implies releasing of mmap sem, while we didn't?

-- 
Peter Xu