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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 B791AC04AB4 for ; Tue, 21 May 2019 08:48:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 96FA92173C for ; Tue, 21 May 2019 08:48:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727126AbfEUIsh (ORCPT ); Tue, 21 May 2019 04:48:37 -0400 Received: from relay.sw.ru ([185.231.240.75]:48466 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726247AbfEUIsh (ORCPT ); Tue, 21 May 2019 04:48:37 -0400 Received: from [172.16.25.169] by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1hT0Re-0003xT-KR; Tue, 21 May 2019 11:48:26 +0300 Subject: Re: [PATCH v2 2/7] mm: Extend copy_vma() To: "Kirill A. Shutemov" Cc: akpm@linux-foundation.org, dan.j.williams@intel.com, mhocko@suse.com, keith.busch@intel.com, kirill.shutemov@linux.intel.com, alexander.h.duyck@linux.intel.com, ira.weiny@intel.com, andreyknvl@google.com, arunks@codeaurora.org, vbabka@suse.cz, cl@linux.com, riel@surriel.com, keescook@chromium.org, hannes@cmpxchg.org, npiggin@gmail.com, mathieu.desnoyers@efficios.com, shakeelb@google.com, guro@fb.com, aarcange@redhat.com, hughd@google.com, jglisse@redhat.com, mgorman@techsingularity.net, daniel.m.jordan@oracle.com, jannh@google.com, kilobyte@angband.pl, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <155836064844.2441.10911127801797083064.stgit@localhost.localdomain> <155836081252.2441.9024100415314519956.stgit@localhost.localdomain> <20190521081821.fbngbxk7lzwrb7md@box> From: Kirill Tkhai Message-ID: Date: Tue, 21 May 2019 11:48:26 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190521081821.fbngbxk7lzwrb7md@box> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Kirill, On 21.05.2019 11:18, Kirill A. Shutemov wrote: > On Mon, May 20, 2019 at 05:00:12PM +0300, Kirill Tkhai wrote: >> This prepares the function to copy a vma between >> two processes. Two new arguments are introduced. > > This kind of changes requires a lot more explanation in commit message, > describing all possible corner cases> For instance, I would really like to see a story on why logic around > need_rmap_locks is safe after the change. Let me fast answer on the below question firstly, and later I'll write wide explanations, since this requires much more time. >> >> Signed-off-by: Kirill Tkhai >> --- >> include/linux/mm.h | 4 ++-- >> mm/mmap.c | 33 ++++++++++++++++++++++++--------- >> mm/mremap.c | 4 ++-- >> 3 files changed, 28 insertions(+), 13 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 0e8834ac32b7..afe07e4a76f8 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -2329,8 +2329,8 @@ extern void __vma_link_rb(struct mm_struct *, struct vm_area_struct *, >> struct rb_node **, struct rb_node *); >> extern void unlink_file_vma(struct vm_area_struct *); >> extern struct vm_area_struct *copy_vma(struct vm_area_struct **, >> - unsigned long addr, unsigned long len, pgoff_t pgoff, >> - bool *need_rmap_locks); >> + struct mm_struct *, unsigned long addr, unsigned long len, >> + pgoff_t pgoff, bool *need_rmap_locks, bool clear_flags_ctx); >> extern void exit_mmap(struct mm_struct *); >> >> static inline int check_data_rlimit(unsigned long rlim, >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 57803a0a3a5c..99778e724ad1 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -3195,19 +3195,21 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma) >> } >> >> /* >> - * Copy the vma structure to a new location in the same mm, >> - * prior to moving page table entries, to effect an mremap move. >> + * Copy the vma structure to new location in the same vma >> + * prior to moving page table entries, to effect an mremap move; >> */ >> struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, >> - unsigned long addr, unsigned long len, pgoff_t pgoff, >> - bool *need_rmap_locks) >> + struct mm_struct *mm, unsigned long addr, >> + unsigned long len, pgoff_t pgoff, >> + bool *need_rmap_locks, bool clear_flags_ctx) >> { >> struct vm_area_struct *vma = *vmap; >> unsigned long vma_start = vma->vm_start; >> - struct mm_struct *mm = vma->vm_mm; >> + struct vm_userfaultfd_ctx uctx; >> struct vm_area_struct *new_vma, *prev; >> struct rb_node **rb_link, *rb_parent; >> bool faulted_in_anon_vma = true; >> + unsigned long flags; >> >> /* >> * If anonymous vma has not yet been faulted, update new pgoff >> @@ -3220,15 +3222,25 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, >> >> if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) >> return NULL; /* should never get here */ >> - new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags, >> - vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma), >> - vma->vm_userfaultfd_ctx); >> + >> + uctx = vma->vm_userfaultfd_ctx; >> + flags = vma->vm_flags; >> + if (clear_flags_ctx) { >> + uctx = NULL_VM_UFFD_CTX; >> + flags &= ~(VM_UFFD_MISSING | VM_UFFD_WP | VM_MERGEABLE | >> + VM_LOCKED | VM_LOCKONFAULT | VM_WIPEONFORK | >> + VM_DONTCOPY); >> + } > > Why is the new logic required? No justification given. Ditto. >> + >> + new_vma = vma_merge(mm, prev, addr, addr + len, flags, vma->anon_vma, >> + vma->vm_file, pgoff, vma_policy(vma), uctx); >> if (new_vma) { >> /* >> * Source vma may have been merged into new_vma >> */ >> if (unlikely(vma_start >= new_vma->vm_start && >> - vma_start < new_vma->vm_end)) { >> + vma_start < new_vma->vm_end) && >> + vma->vm_mm == mm) { > > How can vma_merge() succeed if vma->vm_mm != mm? We don't use vma as an argument of vma_merge(). We use vma as a source of vma->anon_vma, vma->vm_file and vma_policy(). We search some new_vma in mm with the same characteristics as vma has in vma->vm_mm. In case of success vma_merge() returns it for us. For example, it may success, when vma->vm_mm is mm_struct of forked process, while mm is mm_struct of its parent. [...] Kirill