From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([59.151.112.132]:15121 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751424AbbFLJJQ convert rfc822-to-8bit (ORCPT ); Fri, 12 Jun 2015 05:09:16 -0400 Message-ID: <557AA1B9.9040009@cn.fujitsu.com> Date: Fri, 12 Jun 2015 17:09:13 +0800 From: Qu Wenruo MIME-Version: 1.0 To: Tomasz Chmielewski CC: linux-btrfs Subject: Re: kernel crashes with btrfs and busy database IO - how to debug? References: <557A8691.6070908@cn.fujitsu.com> <73cb882c23a71c9039a0e7bbfddfab64@admin.virtall.com> In-Reply-To: <73cb882c23a71c9039a0e7bbfddfab64@admin.virtall.com> Content-Type: text/plain; charset="utf-8"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: -------- Original Message -------- Subject: Re: kernel crashes with btrfs and busy database IO - how to debug? From: Tomasz Chmielewski To: Qu Wenruo Date: 2015年06月12日 16:35 > On 2015-06-12 16:13, Qu Wenruo wrote: > >>> Remote syslog does not capture anything. >> No backtrace? > > No (nothing saved on disk, don't have VNC access). > > The only way to capture anything is: > > while true; do dmesg -c ; done > > but that's usually incomplete. If your dmesg is up-to-date, dmesg -w should do it better than your script. And normally, I can get a full trace with backtrace when kernel down with it. And if it still can't get the full trace, then try kdump. > > >> Without backtrace, it's much harder to debug for us. >> It's quite possible that some codes go mad and pass a NULL pointer, >> and then wait_event() is called on the NULL->some_member. >> >> Anyway, backtrace is needed to debug this. >> >> If syslog can't help, what about kdump + crash to get the backtrace? > > I'll try to get a kdump + crash. > IIRC, kernel from stock RHEL7/centos has kdump enabled. You can try restart kdump service to see what's wrong. Normally you just need to change the crashkernel=auto to some real number. Lastly, it's better to use stock kernel with kdump/crash, or you need a lot of kernel options from debuginfo to max cpu numbers to allow stock crash able to get kernel log from it. Thanks, Qu