linux-kernel - Re: [PATCH v3 01/14] mm: thp: make __split_huge_pmd

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Date:   Mon, 6 Feb 2017 06:12:33 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     Zi Yan <zi.yan@...t.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "minchan@...nel.org" <minchan@...nel.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "khandual@...ux.vnet.ibm.com" <khandual@...ux.vnet.ibm.com>,
        "zi.yan@...rutgers.edu" <zi.yan@...rutgers.edu>,
        Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH v3 01/14] mm: thp: make __split_huge_pmd_locked visible.

On Sun, Feb 05, 2017 at 11:12:39AM -0500, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
> 
> It allows splitting huge pmd while you are holding the pmd lock.
> It is prepared for future zap_pmd_range() use.
> 
> Signed-off-by: Zi Yan <zi.yan@...rutgers.edu>
> ---
>  include/linux/huge_mm.h |  2 ++
>  mm/huge_memory.c        | 22 ++++++++++++----------
>  2 files changed, 14 insertions(+), 10 deletions(-)
> 
...
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 03e4566fc226..cd66532ef667 100644
...
> @@ -2036,10 +2039,9 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>  			clear_page_mlock(page);
>  	} else if (!pmd_devmap(*pmd))
>  		goto out;
> -	__split_huge_pmd_locked(vma, pmd, haddr, freeze);
> +	__split_huge_pmd_locked(vma, pmd, address, freeze);

Could you explain what is intended on this change?
If some caller (f.e. wp_huge_pmd?) could call __split_huge_pmd() with
address not aligned with pmd border, __split_huge_pmd_locked() results in
triggering VM_BUG_ON(haddr & ~HPAGE_PMD_MASK).

Thanks,
Naoya Horiguchi

>  out:
>  	spin_unlock(ptl);
> -	mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
>  }
>  
>  void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
> -- 
> 2.11.0
>