linux-kernel - Re: [PATCH v2 2/2] hugetlbfs: Use i_mmap_rwsem to fix page fault/truncate race

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Message-ID: <20181222221411.ktm5qeebi43lvce5@kshutemo-mobl1>
Date:   Sun, 23 Dec 2018 01:14:12 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "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>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] hugetlbfs: Use i_mmap_rwsem to fix page
 fault/truncate race

On Fri, Dec 21, 2018 at 02:17:32PM -0800, Mike Kravetz wrote:
> Am I misunderstanding your question/concern?

No. Thanks for the clarification.

> 
> I have decided to add the locking (although unnecessary) with something like
> this in hugetlbfs_evict_inode.
> 
> 	/*
> 	 * The vfs layer guarantees that there are no other users of this
> 	 * inode.  Therefore, it would be safe to call remove_inode_hugepages
> 	 * without holding i_mmap_rwsem.  We acquire and hold here to be
> 	 * consistent with other callers.  Since there will be no contention
> 	 * on the semaphore, overhead is negligible.
> 	 */
> 	i_mmap_lock_write(mapping);
> 	remove_inode_hugepages(inode, 0, LLONG_MAX);
> 	i_mmap_unlock_write(mapping);

LGTM.

-- 
 Kirill A. Shutemov