From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752145AbdK0MnB (ORCPT ); Mon, 27 Nov 2017 07:43:01 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:60546 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751725AbdK0Mm7 (ORCPT ); Mon, 27 Nov 2017 07:42:59 -0500 Date: Mon, 27 Nov 2017 14:42:49 +0200 From: Mike Rapoport To: Michal Hocko Cc: guoxuenan , akpm@linux-foundation.org, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, miaoxie@huawei.com, shli@fb.com, aarcange@redhat.com, mgorman@techsingularity.net, kirill.shutemov@linux.intel.com, rientjes@google.com, khandual@linux.vnet.ibm.com, riel@redhat.com Subject: Re: [PATCH] mm,madvise: bugfix of madvise systemcall infinite loop under special circumstances. References: <20171127115318.911-1-guoxuenan@huawei.com> <20171127115847.7b65btmfl762552d@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20171127115847.7b65btmfl762552d@dhcp22.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 17112712-0040-0000-0000-000003F2F53E X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17112712-0041-0000-0000-000025F5CEEB Message-Id: <20171127124248.GA10946@rapoport-lnx> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-11-27_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1711270176 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 27, 2017 at 12:58:47PM +0100, Michal Hocko wrote: > On Mon 27-11-17 19:53:18, guoxuenan wrote: > > From: chenjie > > > > The madvise() system call supported a set of "conventional" advice values, > > the MADV_WILLNEED parameter has possibility of triggering an infinite loop under > > direct access mode(DAX). > > > > Infinite loop situation: > > 1、initial state [ start = vam->vm_start < vam->vm_end < end ]. > > 2、madvise_vma() using MADV_WILLNEED parameter; > > madvise_vma() -> madvise_willneed() -> return 0 && the value of [prev] is not updated. > > > > In function SYSCALL_DEFINE3(madvise,...) > > When [start = vam->vm_start] the program enters "for" loop, > > find_vma_prev() will set the pointer vma and the pointer prev(prev = vam->vm_prev). > > Normally ,madvise_vma() will always move the pointer prev ,but when use DAX mode, > > it will never update the value of [prev]. > > > > ======================================================================= > > SYSCALL_DEFINE3(madvise,...) > > { > > [...] > > //start = vam->start => prev=vma->prev > > vma = find_vma_prev(current->mm, start, &prev); > > [...] > > for(;;) > > { > > update [start = vma->vm_start] > > > > con0: if (start >= end) //false always; > > goto out; > > tmp = vma->vm_end; > > > > //do not update [prev] and always return 0; > > error = madvise_willneed(); > > > > con1: if (error) //false always; > > goto out; > > > > //[ vam->vm_start < start = vam->vm_end > update [start = tmp ] > > > > con2: if (start >= end) //false always ; > > goto out; > > > > //because of pointer [prev] did not change,[vma] keep as it was; > > update [ vma = prev->vm_next ] > > } > > [...] > > } > > ======================================================================= > > After the first cycle ;it will always keep > > vam->vm_start < start = vam->vm_end < end && vma = prev->vm_next; > > since Circulation exit conditions (con{0,1,2}) will never meet ,the > > program stuck in infinite loop. > > I find your changelog a bit hard to parse. What would you think about > the following: > " > MADVISE_WILLNEED has always been a noop for DAX (formerly XIP) mappings. > Unfortunatelly madvise_willneed doesn't communicate this information > properly to the generic madvise syscall implementation. The calling > converion is quite subtle there. madvise_vma is supposed to either spelling: "The calling convention" > return an error or update &prev otherwise the main loop will never > advance to the next vma and it will keep looping for ever without a way > to get out of the kernel. > > It seems this has been broken since introduced. Nobody has noticed > because nobody seems to be using MADVISE_WILLNEED on these DAX mappings. > > Fixes: fe77ba6f4f97 ("[PATCH] xip: madvice/fadvice: execute in place") > Cc: stable > " > > > Signed-off-by: chenjie > > Signed-off-by: guoxuenan > > Other than that > Acked-by: Michal Hocko > > > --- > > mm/madvise.c | 4 +--- > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > index 375cf32..751e97a 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -276,15 +276,14 @@ static long madvise_willneed(struct vm_area_struct *vma, > > { > > struct file *file = vma->vm_file; > > > > + *prev = vma; > > #ifdef CONFIG_SWAP > > if (!file) { > > - *prev = vma; > > force_swapin_readahead(vma, start, end); > > return 0; > > } > > > > if (shmem_mapping(file->f_mapping)) { > > - *prev = vma; > > force_shm_swapin_readahead(vma, start, end, > > file->f_mapping); > > return 0; > > @@ -299,7 +298,6 @@ static long madvise_willneed(struct vm_area_struct *vma, > > return 0; > > } > > > > - *prev = vma; > > start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; > > if (end > vma->vm_end) > > end = vma->vm_end; > > -- > > 2.9.5 > > > > -- > Michal Hocko > SUSE Labs > -- Sincerely yours, Mike.