From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f181.google.com (mail-ig0-f181.google.com [209.85.213.181]) by kanga.kvack.org (Postfix) with ESMTP id 7A6A26B007B for ; Tue, 27 May 2014 08:10:27 -0400 (EDT) Received: by mail-ig0-f181.google.com with SMTP id h3so959769igd.2 for ; Tue, 27 May 2014 05:10:27 -0700 (PDT) Received: from mail-ig0-x229.google.com (mail-ig0-x229.google.com [2607:f8b0:4001:c05::229]) by mx.google.com with ESMTPS id b20si25708276icc.25.2014.05.27.05.10.26 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 27 May 2014 05:10:26 -0700 (PDT) Received: by mail-ig0-f169.google.com with SMTP id hl10so953776igb.4 for ; Tue, 27 May 2014 05:10:26 -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 17:40:26 +0530 Message-ID: Subject: Re: [PATCH] mm: fix zero page check in vm_normal_page From: vinayak menon Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Konstantin Khlebnikov 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 5:18 PM, Konstantin Khlebnikov wrote: > 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. Ok. But in vm_normal_page shouldn't we check for zero_pfn in the case of VM_MIXEDMAP ? -- 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