From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f42.google.com (mail-qg0-f42.google.com [209.85.192.42]) by kanga.kvack.org (Postfix) with ESMTP id A70C06B026A for ; Mon, 4 Apr 2016 08:03:57 -0400 (EDT) Received: by mail-qg0-f42.google.com with SMTP id j35so146929339qge.0 for ; Mon, 04 Apr 2016 05:03:57 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id d26si12993093wmi.104.2016.04.04.05.03.56 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 04 Apr 2016 05:03:56 -0700 (PDT) Subject: Re: mm: BUG in khugepaged_scan_mm_slot References: From: Vlastimil Babka Message-ID: <5702582A.1030904@suse.cz> Date: Mon, 4 Apr 2016 14:03:54 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Vyukov , Andrew Morton , "Kirill A. Shutemov" , "linux-mm@kvack.org" , LKML , Hugh Dickins , Greg Thelen , Konstantin Khlebnikov Cc: syzkaller , Kostya Serebryany , Alexander Potapenko , Sasha Levin , Andrea Arcangeli [+CC Andrea] On 04/02/2016 11:48 AM, Dmitry Vyukov wrote: > Hello, > > The following program triggers a BUG in khugepaged_scan_mm_slot: > > > vma ffff880032698f90 start 0000000020c57000 end 0000000020c58000 > next ffff88003269a1b8 prev ffff88003269ac18 mm ffff88005e274780 > prot 35 anon_vma ffff88003182c000 vm_ops (null) > pgoff fed00 file ffff8800324552c0 private_data (null) > flags: 0x5144477(read|write|exec|mayread|maywrite|mayexec|pfnmap|io|dontexpand|account) > ------------[ cut here ]------------ > kernel BUG at mm/huge_memory.c:2313! > invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN That's VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma) in hugepage_vma_check(). #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE) #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_PFNMAP | VM_MIXEDMAP) Of those, we have VM_IO | VM_DONTEXPAND. I don't know if it's valid for a vma with anon_vma to have such flags, if yes, we should probably modify hugepage_vma_check(). Called from khugepaged_scan_mm_slot() it should just return false out VM_NO_THP. Called from collapse_huge_page() it could keep the VM_BUG_ON. Or maybe just have VM_BUG_ON(!hugepage_vma_check()) there? Hmm actually no, there's a mmap_sem release for read and then acquire for write, so we can't rely on the check done earlier from khugepaged_scan_mm_slot(). So we should probably just change the VM_BUG_ON to another "return false" condition. Unless the VM_BUG_ON uncovered a real bug and the earlier conditions in hugepage_vma_check() should guarantee the VM_BUG_ON be false for any vma. -- 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