From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762386AbdEWIuu (ORCPT ); Tue, 23 May 2017 04:50:50 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:48333 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1760478AbdEWIup (ORCPT ); Tue, 23 May 2017 04:50:45 -0400 Subject: Re: [PATCH 2/2] Save current timestamp part of dmesg while writing oops message to pstore To: Kees Cook Cc: Anton Vorontsov , Colin Cross , Tony Luck , LKML , "mahesh@linux.vnet.ibm.com" , Hari Bathini , hegdevasant@linux.vnet.ibm.com References: <1495448437-15398-1-git-send-email-ankit@linux.vnet.ibm.com> <1495448437-15398-2-git-send-email-ankit@linux.vnet.ibm.com> From: Ankit Kumar Date: Tue, 23 May 2017 14:19:47 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-TM-AS-MML: disable x-cbid: 17052308-0040-0000-0000-0000031C58C5 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17052308-0041-0000-0000-00000C952177 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-23_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1705230045 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Kees, On Tuesday 23 May 2017 05:21 AM, Kees Cook wrote: > On Mon, May 22, 2017 at 3:20 AM, Ankit Kumar wrote: >> Currently on panic or Oops, kernel saves the last few bytes from dmesg >> buffer to nvram. Usually kdump does capture kernel memory and provide >> dmesg logs as well. But in some cases where kdump fails to capture >> vmcore, the dmesg buffer stored in nvram/pstore turns out to be very >> helpful in analyzing root cause. >> >> Present code creates pstore dump file(/sys/fs/pstore/dmesg-***) based on >> timestamp(retrieved from header). Current pstore code creates dump file >> (/sys/fs/pstore/dmesg-***) with that timestamp. Dump file can be analyzed >> based on file creation time and we can make out whether dump file has latest >> data or not. >> >> But when we transfer pstore dump file(/sys/fs/pstore/dmesg-***) to other >> machine or collect file using some utilities(sosreport/supportconfig) then file >> timestamp gets changed and hence by looking at device file (dmesg-***) we won't >> be able to identify whether dump has latest data or not. >> >> Above issue can be fixed if we also have timestamp(dump creation time) as >> initial few bytes while capturing dmesg buffer to pstore dump file >> (/sys/fs/pstore/dmesg-***). >> >> >> This patch enhances pstore write code to also write timestamp as part of data. >> >> Here is sample log of dump file:(/sys/fs/pstore/dmesg-***) >> Oops#1 Part1 [timestamp:1494939359.590463] > While I understand your rationale about possibly losing file timestamp > information in userspace, I think this is a solvable problem on the > collection side. If an additional header is needed, perhaps copy the > dmesg files like this: > > for i in dmesg-*; do > (stat --format=%y /sys/fs/pstore/$i; \ > cat /sys/fs/pstore/$i) > $collect_dir/$i > done Yes. We can handle this in userspace. But we wanted to see if we can add this as part of pstore log itself. > One of the primary concerns for pstore is the stored dump size, I understand. How about adding timestamp to file name itself? Something like below index 792a4e5..0837365 100644 --- a/fs/pstore/inode.c +++ b/fs/pstore/inode.c @@ -349,9 +349,10 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record) switch (record->type) { case PSTORE_TYPE_DMESG: - scnprintf(name, sizeof(name), "dmesg-%s-%lld%s", + scnprintf(name, sizeof(name), "dmesg-%s-%lld%s-%lu.%lu", record->psi->name, record->id, - record->compressed ? ".enc.z" : ""); + record->compressed ? ".enc.z" : "", + record->time.tv_sec, record->time.tv_nsec / 1000); break; case PSTORE_TYPE_CONSOLE: ~Ankit