From: Vlastimil Babka <vbabka@suse.cz>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] thp: fix MADV_DONTNEED vs. numa balancing race
Date: Wed, 12 Apr 2017 15:33:35 +0200 [thread overview]
Message-ID: <f105f6a5-bb5e-9480-6b2e-d2d15f631af9@suse.cz> (raw)
In-Reply-To: <20170302151034.27829-3-kirill.shutemov@linux.intel.com>
On 03/02/2017 04:10 PM, Kirill A. Shutemov wrote:
> In case prot_numa, we are under down_read(mmap_sem). It's critical
> to not clear pmd intermittently to avoid race with MADV_DONTNEED
> which is also under down_read(mmap_sem):
>
> CPU0: CPU1:
> change_huge_pmd(prot_numa=1)
> pmdp_huge_get_and_clear_notify()
> madvise_dontneed()
> zap_pmd_range()
> pmd_trans_huge(*pmd) == 0 (without ptl)
> // skip the pmd
> set_pmd_at();
> // pmd is re-established
>
> The race makes MADV_DONTNEED miss the huge pmd and don't clear it
> which may break userspace.
>
> Found by code analysis, never saw triggered.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> mm/huge_memory.c | 34 +++++++++++++++++++++++++++++++++-
> 1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index e7ce73b2b208..bb2b3646bd78 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1744,7 +1744,39 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> if (prot_numa && pmd_protnone(*pmd))
> goto unlock;
>
> - entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
> + /*
> + * In case prot_numa, we are under down_read(mmap_sem). It's critical
> + * to not clear pmd intermittently to avoid race with MADV_DONTNEED
> + * which is also under down_read(mmap_sem):
> + *
> + * CPU0: CPU1:
> + * change_huge_pmd(prot_numa=1)
> + * pmdp_huge_get_and_clear_notify()
> + * madvise_dontneed()
> + * zap_pmd_range()
> + * pmd_trans_huge(*pmd) == 0 (without ptl)
> + * // skip the pmd
> + * set_pmd_at();
> + * // pmd is re-established
> + *
> + * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
> + * which may break userspace.
> + *
> + * pmdp_invalidate() is required to make sure we don't miss
> + * dirty/young flags set by hardware.
> + */
> + entry = *pmd;
> + pmdp_invalidate(vma, addr, pmd);
> +
> + /*
> + * Recover dirty/young flags. It relies on pmdp_invalidate to not
> + * corrupt them.
> + */
pmdp_invalidate() does:
pmd_t entry = *pmdp;
set_pmd_at(vma->vm_mm, address, pmdp, pmd_mknotpresent(entry));
so it's not atomic and if CPU sets dirty or accessed in the middle of
this, they will be lost?
But I don't see how the other invalidate caller
__split_huge_pmd_locked() deals with this either. Andrea, any idea?
Vlastimil
> + if (pmd_dirty(*pmd))
> + entry = pmd_mkdirty(entry);
> + if (pmd_young(*pmd))
> + entry = pmd_mkyoung(entry);
> +
> entry = pmd_modify(entry, newprot);
> if (preserve_write)
> entry = pmd_mk_savedwrite(entry);
>
next prev parent reply other threads:[~2017-04-12 13:33 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-02 15:10 [PATCH 0/4] thp: fix few MADV_DONTNEED races Kirill A. Shutemov
2017-03-02 15:10 ` [PATCH 1/4] thp: reduce indentation level in change_huge_pmd() Kirill A. Shutemov
2017-04-12 11:37 ` Vlastimil Babka
2017-03-02 15:10 ` [PATCH 2/4] thp: fix MADV_DONTNEED vs. numa balancing race Kirill A. Shutemov
2017-03-03 17:17 ` Dave Hansen
2017-04-12 13:33 ` Vlastimil Babka [this message]
2017-05-16 14:54 ` Vlastimil Babka
2017-05-16 20:29 ` Andrea Arcangeli
2017-05-23 12:42 ` Vlastimil Babka
2017-06-09 8:21 ` Vlastimil Babka
2017-03-02 15:10 ` [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race Kirill A. Shutemov
2017-03-03 5:35 ` Hillf Danton
2017-03-03 10:26 ` Kirill A. Shutemov
2017-03-06 1:44 ` Minchan Kim
2017-03-07 14:04 ` Kirill A. Shutemov
2017-03-06 2:49 ` Aneesh Kumar K.V
2017-03-07 13:52 ` Kirill A. Shutemov
2017-03-02 15:10 ` [PATCH 4/4] thp: fix MADV_DONTNEED vs clear soft dirty race Kirill A. Shutemov
2017-03-03 22:29 ` Andrew Morton
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