Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752102AbdHHKgO (ORCPT ); Tue, 8 Aug 2017 06:36:14 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:36096 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751464AbdHHKgN (ORCPT ); Tue, 8 Aug 2017 06:36:13 -0400 Subject: Re: [RFC v5 03/11] mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE To: Laurent Dufour , paulmck@linux.vnet.ibm.com, peterz@infradead.org, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox References: <1497635555-25679-1-git-send-email-ldufour@linux.vnet.ibm.com> <1497635555-25679-4-git-send-email-ldufour@linux.vnet.ibm.com> Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen From: Anshuman Khandual Date: Tue, 8 Aug 2017 16:05:07 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <1497635555-25679-4-git-send-email-ldufour@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17080810-0004-0000-0000-00000229BEC2 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17080810-0005-0000-0000-00005E0FED9E Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-08_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1706020000 definitions=main-1708080170 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2094 Lines: 61 On 06/16/2017 11:22 PM, Laurent Dufour wrote: > When handling page fault without holding the mmap_sem the fetch of the > pte lock pointer and the locking will have to be done while ensuring > that the VMA is not touched in our back. It does not change things from whats happening right now, where do we check that VMA has not changed by now ? > > So move the fetch and locking operations in a dedicated function. > > Signed-off-by: Laurent Dufour > --- > mm/memory.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 40834444ea0d..f1132f7931ef 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2240,6 +2240,13 @@ static inline void wp_page_reuse(struct vm_fault *vmf) > pte_unmap_unlock(vmf->pte, vmf->ptl); > } > > +static bool pte_spinlock(struct vm_fault *vmf) > +{ > + vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd); > + spin_lock(vmf->ptl); > + return true; > +} > + Moving them together makes sense but again if blocks are redundant when it returns true all the time. > static bool pte_map_lock(struct vm_fault *vmf) > { > vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); > @@ -3552,8 +3559,8 @@ static int do_numa_page(struct vm_fault *vmf) > * validation through pte_unmap_same(). It's of NUMA type but > * the pfn may be screwed if the read is non atomic. > */ > - vmf->ptl = pte_lockptr(vma->vm_mm, vmf->pmd); > - spin_lock(vmf->ptl); > + if (!pte_spinlock(vmf)) > + return VM_FAULT_RETRY; > if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) { > pte_unmap_unlock(vmf->pte, vmf->ptl); > goto out; > @@ -3745,8 +3752,8 @@ static int handle_pte_fault(struct vm_fault *vmf) > if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma)) > return do_numa_page(vmf); > > - vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd); > - spin_lock(vmf->ptl); > + if (!pte_spinlock(vmf)) > + return VM_FAULT_RETRY; > entry = vmf->orig_pte; > if (unlikely(!pte_same(*vmf->pte, entry))) > goto unlock; >