linux-kernel - Re: [PATCH 3/3] hugetlb: allocate vma lock for all sharable vmas

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Date:   Sat, 15 Oct 2022 09:40:18 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
CC:     Muchun Song <songmuchun@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Michal Hocko <mhocko@...e.com>, Peter Xu <peterx@...hat.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Prakash Sangappa <prakash.sangappa@...cle.com>,
        James Houghton <jthoughton@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Ray Fucillo <Ray.Fucillo@...ersystems.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3] hugetlb: allocate vma lock for all sharable vmas

On 2022/10/5 9:17, Mike Kravetz wrote:
> The hugetlb vma lock was originally designed to synchronize pmd sharing.
> As such, it was only necessary to allocate the lock for vmas that were
> capable of pmd sharing.  Later in the development cycle, it was discovered
> that it could also be used to simplify fault/truncation races as described
> in [1].  However, a subsequent change to allocate the lock for all vmas
> that use the page cache was never made.  A fault/truncation race could
> leave pages in a file past i_size until the file is removed.
> 
> Remove the previous restriction and allocate lock for all VM_MAYSHARE
> vmas.  Warn in the unlikely event of allocation failure.
> 
> Fixes: "hugetlb: clean up code checking for fault/truncation races"
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

I believe this is a feasible solution. Thanks.

Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

Thanks,
Miaohe Lin