From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753124AbcIIIZB (ORCPT ); Fri, 9 Sep 2016 04:25:01 -0400 Received: from mga04.intel.com ([192.55.52.120]:35715 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752481AbcIIIY4 (ORCPT ); Fri, 9 Sep 2016 04:24:56 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.30,304,1470726000"; d="scan'208";a="6369972" Subject: Re: [PATCH] Fix region lost in /proc/self/smaps To: Dave Hansen , pbonzini@redhat.com, akpm@linux-foundation.org, mhocko@suse.com, dan.j.williams@intel.com References: <1473231111-38058-1-git-send-email-guangrong.xiao@linux.intel.com> <57D04192.5070704@intel.com> <8b800d72-9b28-237c-47a6-604d98a40315@linux.intel.com> <57D1703E.4070504@intel.com> Cc: gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, stefanha@redhat.com, yuhuang@redhat.com, linux-mm@kvack.org, ross.zwisler@linux.intel.com From: Xiao Guangrong Message-ID: <01bcbbe2-5560-ea42-4d75-6ab50c3060d4@linux.intel.com> Date: Fri, 9 Sep 2016 16:19:15 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <57D1703E.4070504@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/08/2016 10:05 PM, Dave Hansen wrote: > On 09/07/2016 08:36 PM, Xiao Guangrong wrote:>> The user will see two > VMAs in their output: >>> >>> A: 0x1000->0x2000 >>> C: 0x1000->0x3000 >>> >>> Will it confuse them to see the same virtual address range twice? Or is >>> there something preventing that happening that I'm missing? >>> >> >> You are right. Nothing can prevent it. >> >> However, it is not easy to handle the case that the new VMA overlays >> with the old VMA >> already got by userspace. I think we have some choices: >> 1: One way is completely skipping the new VMA region as current kernel >> code does but i >> do not think this is good as the later VMAs will be dropped. >> >> 2: show the un-overlayed portion of new VMA. In your case, we just show >> the region >> (0x2000 -> 0x3000), however, it can not work well if the VMA is a new >> created >> region with different attributions. >> >> 3: completely show the new VMA as this patch does. >> >> Which one do you prefer? > > I'd be willing to bet that #3 will break *somebody's* tooling. > Addresses going backwards is certainly screwy. Imagine somebody using > smaps to search for address holes and doing hole_size=0x1000-0x2000. > > #1 can lies about there being no mapping in place where there there may > have _always_ been a mapping and is very similar to the bug you were > originally fixing. I think that throws it out. > > #2 is our best bet, I think. It's unfortunately also the most code. > It's also a bit of a fib because it'll show a mapping that never > actually existed, but I think this is OK. I'm not sure what the > downside is that you're referring to, though. Can you explain? Yes. I was talking the case as follows: 1: read() #1: prints vma-A(0x1000 -> 0x2000) 2: unmap vma-A(0x1000 -> 0x2000) 3: create vma-B(0x80 -> 0x3000) on other file with different permission (w, r, x) 4: read #2: prints vma-B(0x2000 -> 0x3000) Then userspace will get just a portion of vma-B. well, maybe it is not too bad. :) How about this changes: diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 187d84e..10ca648 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -147,7 +147,7 @@ m_next_vma(struct proc_maps_private *priv, struct vm_area_struct *vma) static void m_cache_vma(struct seq_file *m, struct vm_area_struct *vma) { if (m->count < m->size) /* vma is copied successfully */ - m->version = m_next_vma(m->private, vma) ? vma->vm_start : -1UL; + m->version = m_next_vma(m->private, vma) ? vma->vm_end : -1UL; } static void *m_start(struct seq_file *m, loff_t *ppos) @@ -176,14 +176,14 @@ static void *m_start(struct seq_file *m, loff_t *ppos) if (last_addr) { vma = find_vma(mm, last_addr); - if (vma && (vma = m_next_vma(priv, vma))) + if (vma) return vma; } m->version = 0; if (pos < mm->map_count) { for (vma = mm->mmap; pos; pos--) { - m->version = vma->vm_start; + m->version = vma->vm_end; vma = vma->vm_next; } return vma; @@ -293,7 +293,7 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid) vm_flags_t flags = vma->vm_flags; unsigned long ino = 0; unsigned long long pgoff = 0; - unsigned long start, end; + unsigned long end, start = m->version; dev_t dev = 0; const char *name = NULL; @@ -304,8 +304,13 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid) pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT; } + /* + * the region [0, m->version) has already been handled, do not + * handle it doubly. + */ + start = max(vma->vm_start, start); + /* We don't show the stack guard page in /proc/maps */ - start = vma->vm_start; if (stack_guard_page_start(vma, start)) start += PAGE_SIZE; end = vma->vm_end;