linux-kernel - Re: [PATCH v1] hugetlb, userfaultfd: Fix reservation restore on userfaultfd error

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Date:   Tue, 16 Nov 2021 16:32:52 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mina Almasry <almasrymina@...gle.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Wei Xu <weixugc@...gle.com>,
        James Houghton <jthoughton@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] hugetlb, userfaultfd: Fix reservation restore on
 userfaultfd error

On Tue, 16 Nov 2021 15:57:32 -0800 Mina Almasry <almasrymina@...gle.com> wrote:

> Currently in the is_continue case in hugetlb_mcopy_atomic_pte(), if we
> bail out using "goto out_release_unlock;" in the cases where idx >=
> size, or !huge_pte_none(), the code will detect that new_pagecache_page
> == false, and so call restore_reserve_on_error().
> In this case I see restore_reserve_on_error() delete the reservation,
> and the following call to remove_inode_hugepages() will increment
> h->resv_hugepages causing a 100% reproducible leak.
> 
> We should treat the is_continue case similar to adding a page into the
> pagecache and set new_pagecache_page to true, to indicate that there is
> no reservation to restore on the error path, and we need not call
> restore_reserve_on_error().
> 
> Cc: Wei Xu <weixugc@...gle.com>
> 
> Fixes: c7b1850dfb41 ("hugetlb: don't pass page cache pages to restore_reserve_on_error")

I added cc:stable to this.