From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0C82C46464 for ; Fri, 10 Aug 2018 10:49:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A795F22404 for ; Fri, 10 Aug 2018 10:49:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A795F22404 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727781AbeHJNSa (ORCPT ); Fri, 10 Aug 2018 09:18:30 -0400 Received: from mx2.suse.de ([195.135.220.15]:55994 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726963AbeHJNSa (ORCPT ); Fri, 10 Aug 2018 09:18:30 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id DF291B011; Fri, 10 Aug 2018 10:49:07 +0000 (UTC) Subject: Re: [RFC v7 PATCH 4/4] mm: unmap special vmas with regular do_munmap() To: Yang Shi , mhocko@kernel.org, willy@infradead.org, ldufour@linux.vnet.ibm.com, kirill@shutemov.name, akpm@linux-foundation.org, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1533857763-43527-1-git-send-email-yang.shi@linux.alibaba.com> <1533857763-43527-5-git-send-email-yang.shi@linux.alibaba.com> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1533857763-43527-5-git-send-email-yang.shi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/10/2018 01:36 AM, Yang Shi wrote: > Unmapping vmas, which have VM_HUGETLB | VM_PFNMAP flag set or > have uprobes set, need get done with write mmap_sem held since > they may update vm_flags. > > So, it might be not safe enough to deal with these kind of special > mappings with read mmap_sem. Deal with such mappings with regular > do_munmap() call. > > Michal suggested to make this as a separate patch for safer and more > bisectable sake. > > Cc: Michal Hocko > Signed-off-by: Yang Shi > --- > mm/mmap.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 2234d5a..06cb83c 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2766,6 +2766,16 @@ static inline void munlock_vmas(struct vm_area_struct *vma, > } > } > > +static inline bool can_zap_with_rlock(struct vm_area_struct *vma) > +{ > + if ((vma->vm_file && > + vma_has_uprobes(vma, vma->vm_start, vma->vm_end)) | vma_has_uprobes() seems to be rather expensive check with e.g. unconditional spinlock. uprobe_munmap() seems to have some precondition cheaper checks for e.g. cases when there's no uprobes in the system (should be common?). BTW, uprobe_munmap() touches mm->flags, not vma->flags, so it should be evaluated more carefully for being called under mmap sem for reading, as having vmas already detached is no guarantee. > + (vma->vm_flags | (VM_HUGETLB | VM_PFNMAP))) ^ I think replace '|' with '&' here? > + return false; > + > + return true; > +} > + > /* > * Zap pages with read mmap_sem held > * > @@ -2808,6 +2818,17 @@ static int do_munmap_zap_rlock(struct mm_struct *mm, unsigned long start, > goto out; > } > > + /* > + * Unmapping vmas, which have VM_HUGETLB | VM_PFNMAP flag set or > + * have uprobes set, need get done with write mmap_sem held since > + * they may update vm_flags. Deal with such mappings with regular > + * do_munmap() call. > + */ > + for (vma = start_vma; vma && vma->vm_start < end; vma = vma->vm_next) { > + if (!can_zap_with_rlock(vma)) > + goto regular_path; > + } > + > /* Handle mlocked vmas */ > if (mm->locked_vm) { > vma = start_vma; > @@ -2828,6 +2849,9 @@ static int do_munmap_zap_rlock(struct mm_struct *mm, unsigned long start, > > return 0; > > +regular_path: I think it's missing a down_write_* here. > + ret = do_munmap(mm, start, len, uf); > + > out: > up_write(&mm->mmap_sem); > return ret; >