From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f182.google.com (mail-ie0-f182.google.com [209.85.223.182]) by kanga.kvack.org (Postfix) with ESMTP id 574C36B0073 for ; Tue, 27 May 2014 07:48:19 -0400 (EDT) Received: by mail-ie0-f182.google.com with SMTP id x19so1298799ier.41 for ; Tue, 27 May 2014 04:48:19 -0700 (PDT) Received: from mail-ie0-x233.google.com (mail-ie0-x233.google.com [2607:f8b0:4001:c03::233]) by mx.google.com with ESMTPS id z2si4973555igl.49.2014.05.27.04.48.18 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 27 May 2014 04:48:18 -0700 (PDT) Received: by mail-ie0-f179.google.com with SMTP id rd18so8638479iec.38 for ; Tue, 27 May 2014 04:48:18 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1401166595-4792-1-git-send-email-vinayakm.list@gmail.com> <20140527103130.3A04BE009B@blue.fi.intel.com> Date: Tue, 27 May 2014 15:48:18 +0400 Message-ID: Subject: Re: [PATCH] mm: fix zero page check in vm_normal_page From: Konstantin Khlebnikov Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: vinayak menon Cc: "Kirill A. Shutemov" , "linux-mm@kvack.org" , Johannes Weiner , Mel Gorman , Rik van Riel , Ingo Molnar , Peter Zijlstra , Andrew Morton On Tue, May 27, 2014 at 3:43 PM, vinayak menon wrote: > On Tue, May 27, 2014 at 5:01 PM, Konstantin Khlebnikov wrote: >> On Tue, May 27, 2014 at 2:31 PM, Kirill A. Shutemov >> wrote: >>> Vinayak Menon wrote: >>>> An issue was observed when a userspace task exits. >>>> The page which hits error here is the zero page. >>>> In zap_pte_range, vm_normal_page gets called, and it >>>> returns a page address and not NULL, even though the >>>> pte corresponds to zero pfn. In this case, >>>> HAVE_PTE_SPECIAL is not set, and VM_MIXEDMAP is set >>>> in vm_flags. In the case of VM_MIXEDMAP , only pfn_valid >>>> is checked, and not is_zero_pfn. This results in >>>> zero page being returned instead of NULL. >>>> >>>> BUG: Bad page map in process mediaserver pte:9dff379f pmd:9bfbd831 >>>> page:c0ed8e60 count:1 mapcount:-1 mapping: (null) index:0x0 >>>> page flags: 0x404(referenced|reserved) >>>> addr:40c3f000 vm_flags:10220051 anon_vma: (null) mapping:d9fe0764 index:fd >>>> vma->vm_ops->fault: (null) >>>> vma->vm_file->f_op->mmap: binder_mmap+0x0/0x274 >>> >>> How do we get zero_pfn there. We shouldn't use zero page for file mappings. >>> binder does some tricks? >> >> Its vm_ops doesn't provide ->fault method at all. >> Seems like all ptes must be populated at the mmap time. >> For some reason read page fault had happened and handle_pte_fault() >> handled it in do_anonymous_page() which maps zero_page. >> > When the task crashed, it was ptraced by debuggered and the areas were > dumped. And this resulted in the read page fault. Anyway, this bug in the binder. It must either populate all PTEs in ->mmap() or provide ->fault() method. Falling into do_anonymous_page() isn't funny. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org