From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f53.google.com (mail-pa0-f53.google.com [209.85.220.53]) by kanga.kvack.org (Postfix) with ESMTP id DC5046B0035 for ; Wed, 26 Mar 2014 15:55:28 -0400 (EDT) Received: by mail-pa0-f53.google.com with SMTP id ld10so2371566pab.26 for ; Wed, 26 Mar 2014 12:55:28 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTP id tm9si14458815pab.387.2014.03.26.12.55.26 for ; Wed, 26 Mar 2014 12:55:26 -0700 (PDT) Date: Wed, 26 Mar 2014 12:55:25 -0700 From: Andrew Morton Subject: Re: mm: BUG: Bad page state in process ksmd Message-Id: <20140326125525.4e8090096f647f654eb7329d@linux-foundation.org> In-Reply-To: <5332EE97.4050604@oracle.com> References: <5332EE97.4050604@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Sasha Levin Cc: "linux-mm@kvack.org" , LKML , Hugh Dickins On Wed, 26 Mar 2014 11:13:27 -0400 Sasha Levin wrote: > Hi all, > > While fuzzing with trinity inside a KVM tools guest running the latest -next > kernel I've stumbled on the following. (cc Hugh) > Out of curiosity, is there a reason not to do bad flag checks when actually > setting flag? Obviously it'll be slower but it'll be easier catching these > issues. Tricky. Each code site must determine what are and are not valid page states depending upon the current context. The one place where we've made that effort is at the point where a page is returned to the free page pool. Any other sites would require similar amounts of effort and each one would be different from all the others. We do this in a small way all over the place, against individual page flags. grep PageLocked */*.c. > [ 3926.683948] BUG: Bad page state in process ksmd pfn:5a6246 > [ 3926.689336] page:ffffea0016989180 count:0 mapcount:0 mapping: (null) index: > [ 3926.696507] page flags: 0x56fffff8028001c(referenced|uptodate|dirty|swapbacked|mlock > [ 3926.709201] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > [ 3926.711216] bad because of flags: > [ 3926.712136] page flags: 0x200000(mlocked) > [ 3926.713574] Modules linked in: > [ 3926.714466] CPU: 26 PID: 3864 Comm: ksmd Tainted: G W 3.14.0-rc7-next-201 > [ 3926.720942] ffffffff85688060 ffff8806ec7abc38 ffffffff844bd702 0000000000002fa0 > [ 3926.728107] ffffea0016989180 ffff8806ec7abc68 ffffffff844b158f 000fffff80000000 > [ 3926.730563] 0000000000000000 000fffff80000000 ffffffff85688060 ffff8806ec7abcb8 > [ 3926.737653] Call Trace: > [ 3926.738347] dump_stack (lib/dump_stack.c:52) > [ 3926.739841] bad_page (arch/x86/include/asm/atomic.h:38 include/linux/mm.h:432 mm/page_alloc.c:339) > [ 3926.741296] free_pages_prepare (mm/page_alloc.c:644 mm/page_alloc.c:738) > [ 3926.742818] free_hot_cold_page (mm/page_alloc.c:1371) > [ 3926.749425] __put_single_page (mm/swap.c:71) > [ 3926.751074] put_page (mm/swap.c:237) > [ 3926.752398] ksm_do_scan (mm/ksm.c:1480 mm/ksm.c:1704) > [ 3926.753957] ksm_scan_thread (mm/ksm.c:1723) > [ 3926.755940] ? bit_waitqueue (kernel/sched/wait.c:291) > [ 3926.758644] ? ksm_do_scan (mm/ksm.c:1715) > [ 3926.760420] kthread (kernel/kthread.c:219) > [ 3926.761605] ? kthread_create_on_node (kernel/kthread.c:185) > [ 3926.763149] ret_from_fork (arch/x86/kernel/entry_64.S:555) > [ 3926.764323] ? kthread_create_on_node (kernel/kthread.c:185) -- 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