From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f176.google.com (mail-ig0-f176.google.com [209.85.213.176]) by kanga.kvack.org (Postfix) with ESMTP id 345CE6B0035 for ; Wed, 30 Apr 2014 23:57:56 -0400 (EDT) Received: by mail-ig0-f176.google.com with SMTP id hl10so70668igb.3 for ; Wed, 30 Apr 2014 20:57:55 -0700 (PDT) Received: from mail-ie0-x22b.google.com (mail-ie0-x22b.google.com [2607:f8b0:4001:c03::22b]) by mx.google.com with ESMTPS id a5si3863935icf.95.2014.04.30.20.57.55 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 30 Apr 2014 20:57:55 -0700 (PDT) Received: by mail-ie0-f171.google.com with SMTP id to1so3092169ieb.16 for ; Wed, 30 Apr 2014 20:57:55 -0700 (PDT) Date: Wed, 30 Apr 2014 20:56:40 -0700 (PDT) From: Hugh Dickins Subject: Re: [BUG] kernel BUG at mm/vmacache.c:85! In-Reply-To: <53614BFE.9090804@linux.vnet.ibm.com> Message-ID: References: <535EA976.1080402@linux.vnet.ibm.com> <1398723290.25549.20.camel@buesod1.americas.hpqcorp.net> <535F77E8.2040000@linux.vnet.ibm.com> <53614BFE.9090804@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: "Srivatsa S. Bhat" Cc: Linus Torvalds , Davidlohr Bueso , Linux MM , "linux-kernel@vger.kernel.org" , Rik van Riel , Michel Lespinasse , "akpm@linux-foundation.org" , Oleg Nesterov , Dave Jones On Thu, 1 May 2014, Srivatsa S. Bhat wrote: > > I tried to recall the *exact* steps that I had carried out when I first > hit the bug. I realized that I had actually used kexec to boot the new > kernel. I had originally booted into a 3.7.7 kernel that happens to be > on that machine, and then kexec()'ed 3.15-rc3 on it. And that had caused > the kernel crash. Fresh boots of 3.15-rc3, as well as kexec from 3.15+ > to itself, seems to be pretty robust and has never resulted in any bad > behavior (this is why I couldn't reproduce the issue earlier, since I was > doing fresh boots of 3.15-rc). > > So I tried the same recipe again (boot into 3.7.7 and kexec into 3.15-rc3+) > and I got totally random crashes so far, once in sys_kill and two times in > exit_mmap. So I guess the bug is in 3.7.x and probably 3.15-rc is fine after > all... I don't know if we can conclude the bug is in 3.7 rather than 3.15. I spent a little while yesterday looking at your register dumps, and applying scripts/decodecode to your Code lines. I did notice a pattern to the general protection faulting addresses, and the dumps you show today confirm that pattern (but with "1e000000" at the top instead of yesterday's "9e000000"). Sorry, I really cannot spend more time on this, but thought I should at least throw out my observation before moving on. Here I've simply grepped out the lines with the significant pattern (and at least one of these lines is essentially a repetition of the line before, value moved from one register to another with offset subtracted; oh, and that R12 line, "it" has been added on to the vsize acct_collect() already accumulated). RAX: 9e00000005f9e8fd RBX: 000000000000000b RCX: 0000000000000001 RAX: 9e00000005f9e5fd RBX: ffff881031a0c2f8 RCX: ffff88203d52ba40 RDX: 000000000000001e RSI: 9e00000005f9e5a5 RDI: ffff881031a0c2f8 R10: 0000000000000000 R11: 00000000000027d5 R12: 9e000000069d62fd BUG: Bad page map in process kdump pte:1e00000005f98701 pmd:1031489067 BUG: Bad page map in process kdump pte:1e00000005f98701 pmd:103420b067 R13: 0000000000000004 R14: 1e00000005f93403 R15: 000000000000000a That this corruption likes to attack mm structures (vmas yesterday, page tables today) does make me wonder whether mm is to blame. Hugh -- 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