From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f170.google.com (mail-ie0-f170.google.com [209.85.223.170]) by kanga.kvack.org (Postfix) with ESMTP id DE5856B0070 for ; Tue, 27 May 2014 07:31:03 -0400 (EDT) Received: by mail-ie0-f170.google.com with SMTP id at1so8720064iec.29 for ; Tue, 27 May 2014 04:31:03 -0700 (PDT) Received: from mail-ie0-x234.google.com (mail-ie0-x234.google.com [2607:f8b0:4001:c03::234]) by mx.google.com with ESMTPS id z2si4879296igl.49.2014.05.27.04.31.03 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 27 May 2014 04:31:03 -0700 (PDT) Received: by mail-ie0-f180.google.com with SMTP id tp5so8363511ieb.25 for ; Tue, 27 May 2014 04:31:03 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20140527103130.3A04BE009B@blue.fi.intel.com> References: <1401166595-4792-1-git-send-email-vinayakm.list@gmail.com> <20140527103130.3A04BE009B@blue.fi.intel.com> Date: Tue, 27 May 2014 15:31:02 +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: "Kirill A. Shutemov" Cc: Vinayak Menon , "linux-mm@kvack.org" , Johannes Weiner , Mel Gorman , Rik van Riel , Ingo Molnar , Peter Zijlstra , Andrew Morton 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. > >> CPU: 0 PID: 1463 Comm: mediaserver Tainted: G W 3.10.17+ #1 >> [] (unwind_backtrace+0x0/0x11c) from [] (show_stack+0x10/0x14) >> [] (show_stack+0x10/0x14) from [] (print_bad_pte+0x158/0x190) >> [] (print_bad_pte+0x158/0x190) from [] (unmap_single_vma+0x2e4/0x598) >> [] (unmap_single_vma+0x2e4/0x598) from [] (unmap_vmas+0x34/0x50) >> [] (unmap_vmas+0x34/0x50) from [] (exit_mmap+0xc8/0x1e8) >> [] (exit_mmap+0xc8/0x1e8) from [] (mmput+0x54/0xd0) >> [] (mmput+0x54/0xd0) from [] (do_exit+0x360/0x990) >> [] (do_exit+0x360/0x990) from [] (do_group_exit+0x84/0xc0) >> [] (do_group_exit+0x84/0xc0) from [] (get_signal_to_deliver+0x4d4/0x548) >> [] (get_signal_to_deliver+0x4d4/0x548) from [] (do_signal+0xa8/0x3b8) >> >> Signed-off-by: Vinayak Menon >> --- >> mm/memory.c | 2 ++ >> 1 files changed, 2 insertions(+), 0 deletions(-) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index 037b812..c9a5027 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -771,6 +771,8 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, >> if (vma->vm_flags & VM_MIXEDMAP) { >> if (!pfn_valid(pfn)) >> return NULL; >> + if (is_zero_pfn(pfn)) >> + return NULL; >> goto out; >> } else { >> unsigned long off; >> -- >> 1.7.6 >> > > -- > Kirill A. Shutemov > > -- > 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 -- 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