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Message-ID: <CAHS8izM0EjNmyc25fOqsU03G84+nGeyWoXo+oJWC5TQx52OH9A@mail.gmail.com>
Date: Tue, 16 Nov 2021 16:00:35 -0800
From: Mina Almasry <almasrymina@...gle.com>
To: Mike Kravetz <mike.kravetz@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: 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
Hi Mike,
On Tue, Nov 16, 2021 at 3:57 PM 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.
>
Attached is the .c file with the 100% repro.
> 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")
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
> Reported-by: James Houghton <jthoughton@...gle.com>
Not sure if this is a Cc: stable issue. If it is, I can add in v2.
> ---
> mm/hugetlb.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e09159c957e3..25a7a3d84607 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5741,6 +5741,14 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
> page = find_lock_page(mapping, idx);
> if (!page)
> goto out;
> + /*
> + * Set new_pagecache_page to true, as we've added a page to the
> + * pagecache, but userfaultfd hasn't set up a mapping for this
> + * page yet. If we bail out before setting up the mapping, we
> + * want to indicate to restore_reserve_on_error() that we've
> + * added the page to the page cache.
> + */
> + new_pagecache_page = true;
> } else if (!*pagep) {
> /* If a page already exists, then it's UFFDIO_COPY for
> * a non-missing case. Return -EEXIST.
> --
> 2.34.0.rc1.387.gb447b232ab-goog
View attachment "hugetlb-leak-test.c" of type "text/x-csrc" (2964 bytes)
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