From mboxrd@z Thu Jan  1 00:00:00 1970
From: shijie.huang@arm.com (Huang Shijie)
Date: Fri, 4 Nov 2016 10:52:17 +0800
Subject: [PATCH 1/2] arm64: hugetlb: remove the wrong pmd check in
 find_num_contig()
In-Reply-To: <20161104001616.ssjbemliorxi6evl@localhost>
References: <1478140059-13829-1-git-send-email-shijie.huang@arm.com>
 <1478140059-13829-2-git-send-email-shijie.huang@arm.com>
 <20161104001616.ssjbemliorxi6evl@localhost>
Message-ID: <20161104025216.GA19810@sha-win-210.asiapac.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Nov 03, 2016 at 06:16:16PM -0600, Catalin Marinas wrote:
> On Thu, Nov 03, 2016 at 10:27:38AM +0800, Huang Shijie wrote:
> > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> > index 2e49bd2..4811ef1 100644
> > --- a/arch/arm64/mm/hugetlbpage.c
> > +++ b/arch/arm64/mm/hugetlbpage.c
> > @@ -61,10 +61,6 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
> >  		return 1;
> >  	}
> >  	pmd = pmd_offset(pud, addr);
> > -	if (!pmd_present(*pmd)) {
> > -		VM_BUG_ON(!pmd_present(*pmd));
> > -		return 1;
> > -	}
> >  	if ((pte_t *)pmd == ptep) {
> >  		*pgsize = PMD_SIZE;
> >  		return CONT_PMDS;
> 
> BTW, for the !pud_present() and !pgd_present() cases, shouldn't
The kernel will not call the find_num_contig() if the PGD/PUD are empty.
Please see the code in the hugetlb_fault().

   ------------------------------------------------------
	ptep = huge_pte_offset(mm, address);
	if (ptep) {
	    ...............................
	} else {
		ptep = huge_pte_alloc(mm, address, huge_page_size(h));
		if (!ptep)
			return VM_FAULT_OOM;
	}
   ------------------------------------------------------


Thanks
Huang Shijie
> find_num_contig() actually return 0? These are more likely real bugs, so
> no point in setting the huge pte.