From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id 14C876B0033 for ; Mon, 6 Feb 2017 02:44:45 -0500 (EST) Received: by mail-oi0-f72.google.com with SMTP id y140so73958016oie.2 for ; Sun, 05 Feb 2017 23:44:45 -0800 (PST) Received: from tyo161.gate.nec.co.jp (tyo161.gate.nec.co.jp. [114.179.232.161]) by mx.google.com with ESMTPS id x66si13883922oia.49.2017.02.05.23.44.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 05 Feb 2017 23:44:44 -0800 (PST) From: Naoya Horiguchi Subject: Re: [PATCH v3 03/14] mm: use pmd lock instead of racy checks in zap_pmd_range() Date: Mon, 6 Feb 2017 07:43:38 +0000 Message-ID: <20170206074337.GB30339@hori1.linux.bs1.fc.nec.co.jp> References: <20170205161252.85004-1-zi.yan@sent.com> <20170205161252.85004-4-zi.yan@sent.com> In-Reply-To: <20170205161252.85004-4-zi.yan@sent.com> Content-Language: ja-JP Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Zi Yan Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "kirill.shutemov@linux.intel.com" , "akpm@linux-foundation.org" , "minchan@kernel.org" , "vbabka@suse.cz" , "mgorman@techsingularity.net" , "khandual@linux.vnet.ibm.com" , "zi.yan@cs.rutgers.edu" , Zi Yan On Sun, Feb 05, 2017 at 11:12:41AM -0500, Zi Yan wrote: > From: Zi Yan >=20 > Originally, zap_pmd_range() checks pmd value without taking pmd lock. > This can cause pmd_protnone entry not being freed. >=20 > Because there are two steps in changing a pmd entry to a pmd_protnone > entry. First, the pmd entry is cleared to a pmd_none entry, then, > the pmd_none entry is changed into a pmd_protnone entry. > The racy check, even with barrier, might only see the pmd_none entry > in zap_pmd_range(), thus, the mapping is neither split nor zapped. >=20 > Later, in free_pmd_range(), pmd_none_or_clear() will see the > pmd_protnone entry and clear it as a pmd_bad entry. Furthermore, > since the pmd_protnone entry is not properly freed, the corresponding > deposited pte page table is not freed either. >=20 > This causes memory leak or kernel crashing, if VM_BUG_ON() is enabled. >=20 > This patch relies on __split_huge_pmd_locked() and > __zap_huge_pmd_locked(). >=20 > Signed-off-by: Zi Yan > --- > mm/memory.c | 24 +++++++++++------------- > 1 file changed, 11 insertions(+), 13 deletions(-) >=20 > diff --git a/mm/memory.c b/mm/memory.c > index 3929b015faf7..7cfdd5208ef5 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1233,33 +1233,31 @@ static inline unsigned long zap_pmd_range(struct = mmu_gather *tlb, > struct zap_details *details) > { > pmd_t *pmd; > + spinlock_t *ptl; > unsigned long next; > =20 > pmd =3D pmd_offset(pud, addr); > + ptl =3D pmd_lock(vma->vm_mm, pmd); If USE_SPLIT_PMD_PTLOCKS is true, pmd_lock() returns different ptl for each pmd. The following code runs over pmds within [addr, end) with a single ptl (of the first pmd,) so I suspect this locking really works. Maybe pmd_lock() should be called inside while loop? Thanks, Naoya Horiguchi > do { > next =3D pmd_addr_end(addr, end); > if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) { > if (next - addr !=3D HPAGE_PMD_SIZE) { > VM_BUG_ON_VMA(vma_is_anonymous(vma) && > !rwsem_is_locked(&tlb->mm->mmap_sem), vma); > - __split_huge_pmd(vma, pmd, addr, false, NULL); > - } else if (zap_huge_pmd(tlb, vma, pmd, addr)) > - goto next; > + __split_huge_pmd_locked(vma, pmd, addr, false); > + } else if (__zap_huge_pmd_locked(tlb, vma, pmd, addr)) > + continue; > /* fall through */ > } > - /* > - * Here there can be other concurrent MADV_DONTNEED or > - * trans huge page faults running, and if the pmd is > - * none or trans huge it can change under us. This is > - * because MADV_DONTNEED holds the mmap_sem in read > - * mode. > - */ > - if (pmd_none_or_trans_huge_or_clear_bad(pmd)) > - goto next; > + > + if (pmd_none_or_clear_bad(pmd)) > + continue; > + spin_unlock(ptl); > next =3D zap_pte_range(tlb, vma, pmd, addr, next, details); > -next: > cond_resched(); > + spin_lock(ptl); > } while (pmd++, addr =3D next, addr !=3D end); > + spin_unlock(ptl); > =20 > return addr; > } > --=20 > 2.11.0 > = -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org