From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e33.co.us.ibm.com (e33.co.us.ibm.com [32.97.110.151]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e33.co.us.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTP id D571F67A06 for ; Thu, 27 Apr 2006 21:58:02 +1000 (EST) Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by e33.co.us.ibm.com (8.12.11.20060308/8.12.11) with ESMTP id k3RBvwS1027263 for ; Thu, 27 Apr 2006 07:57:58 -0400 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay04.boulder.ibm.com (8.12.10/NCO/VER6.8) with ESMTP id k3RC1StY106404 for ; Thu, 27 Apr 2006 06:01:28 -0600 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.12.11/8.13.3) with ESMTP id k3RBvvvn024538 for ; Thu, 27 Apr 2006 05:57:57 -0600 Date: Thu, 27 Apr 2006 17:27:49 +0530 From: Mohan Kumar M To: Michael Ellerman Subject: Re: [Fastboot] Documentation feedback request. Message-ID: <20060427115749.GA23048@in.ibm.com> References: <444FB2AF.3020802@us.ibm.com> <1146095071.29876.23.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1146095071.29876.23.camel@localhost.localdomain> Cc: linuxppc-dev list , fastboot@lists.osdl.org Reply-To: mohan@in.ibm.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, Apr 27, 2006 at 09:44:31AM +1000, Michael Ellerman wrote: > Hi David, > > Nice work. Few comments below ... > > On Wed, 2006-04-26 at 10:49 -0700, David Wilder wrote: > > Attached is a updated Documentation/kdump/kdump.txt. Please provide > > comments. I will incorporate your feedback and send up to Linus. > > > > plain text document attachment (kdump-final-20060425.txt) > > ================================================================ > > Documentation for Kdump - The kexec-based Crash Dumping Solution > > ================================================================ > > > > This document includes overview, setup and installation, and analysis > > information. > > > > Overview > > ======== > > > > Kdump uses kexec to quickly boot to a dump-capture kernel whenever a > > dump of the system kernel's memory needs to be taken (for example, when > > the system panics). The system kernel's memory image is preserved across > > the reboot and is accessible to the dump-capture kernel. > > > > You can use common Linux commands, such as cp and scp, to copy the > > memory image to a dump file on the local disk, or across the network to > > a remote system. > > > > Kdump and kexec are currently supported on the x86, x86_64, and ppc64 > > architectures. > > s/ppc64/64-bit powerpc/ ? > > > When the system kernel boots, it reserves a small section of memory for > > the dump-capture kernel. This ensures that ongoing Direct Memory Access > > (DMA) from the system kernel does not corrupt the dump-capture kernel. > > The kexec -p command loads the dump-capture kernel into this reserved > > memory. > > Well hopefully ;) > > > On x86 machines, the first 640 KB of physical memory is needed to boot, > > regardless of where the kernel loads. Therefore, kexec backs up this > > region just before rebooting into the dump-capture kernel. > > > > All of the necessary information about the system kernel's core image is > > encoded in the ELF format, and stored in a reserved area of memory > > before a crash. The physical address of the start of the ELF header is > > passed to the dump-capture kernel through the elfcorehdr= boot > > parameter. > > > > With the dump-capture kernel, you can access the memory image, or "old > > memory," in two ways: > > > > - Through a /dev/oldmem device interface. A capture utility can read the > > device file and write out the memory in raw format. This is a raw dump > > of memory. Analysis and capture tools must be intelligent enough to > > determine where to look for the right information. > > > > - Through /proc/vmcore. This exports the dump as an ELF-format file that > > you can write out using file copy commands such as cp or scp. Further, > > you can use analysis tools such as the GNU Debugger (GDB) and the Crash > > tool to debug the dump file. This method ensures that the dump pages are > > correctly ordered. > > > > > > Setup and Installation > > ====================== > > > > Install kexec-tools and the Kdump patch > > --------------------------------------- > > > > 1) Login as the root user. > > > > 2) Download the kexec-tools user-space package from the following URL: > > > > http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz > > > > 3) Unpack the tarball with the tar command, as follows: > > > > tar xvpzf kexec-tools-1.101.tar.gz > > > > 4) Download the latest consolidated Kdump patch from the following URL: > > > > http://lse.sourceforge.net/kdump/ > > > > (This location is being used until all the user-space Kdump patches > > are integrated with the kexec-tools package.) > > > > 5) Change to the kexec-tools-1.101 directory, as follows: > > > > cd kexec-tools-1.101 > > > > 6) Apply the consolidated patch to the kexec-tools-1.101 source tree > > with the patch command, as follows. (Modify the path to the downloaded > > patch as necessary.) > > > > patch -p1 < /path-to-kdump-patch/kexec-tools-1.101-kdump.patch > > > > 7) Configure the package, as follows: > > > > ./configure > > > > 8) Compile the package, as follows: > > > > make > > > > 9) Install the package, as follows: > > > > make install > > > > > > Download and build the system and dump-capture kernels > > ------------------------------------------------------ > > > > Download the mainline (vanilla) kernel source code (2.6.13-rc1 or newer) > > from http://www.kernel.org. Two kernels must be built: a system kernel > > and a dump-capture kernel. Use the following steps to configure these > > kernels with the necessary kexec and Kdump features: > > > > System kernel > > ------------- > > > > 1) Enable "kexec system call" in "Processor type and features." > > > > CONFIG_KEXEC=y > > > > 2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo > > filesystems." This is usually enabled by default. > > > > CONFIG_SYSFS=y > > > > Note that "sysfs file system support" might not appear in the "Pseudo > > filesystems" menu if "Configure standard kernel features (for small > > systems)" is not enabled in "General Setup." In this case, check the > > .config file itself to ensure that sysfs is turned on, as follows: > > > > grep 'CONFIG_SYSFS' .config > > Is there a particular requirement for sysfs? > > > 3) Enable "Compile the kernel with debug info" in "Kernel hacking." > > > > CONFIG_DEBUG_INFO=Y > > > > This causes the kernel to be built with debug symbols. The dump > > analysis tools require a vmlinux with debug symbols in order to read > > and analyze a dump file. > > > > 4) Make and install the kernel and its modules. Update the boot loader > > (such as grub, yaboot, or lilo) configuration files as necessary. > > > > 5) Boot the system kernel with the boot parameter "crashkernel=Y@X", > > where Y specifies how much memory to reserve for the dump-capture kernel > > and X specifies the beginning of this reserved memory. For example, > > "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory > > starting at physical address 0x01000000 for the dump-capture kernel. > > Most of this doesn't apply to powerpc. > > > On x86 and x86_64, use "crashkernel=64M@16M". > > > > On ppc64, use "crashkernel=128M@32M". > > No just use "crashkernel=128M". > May be this is to follow the same convention in other architectures. > > The dump-capture kernel > > ----------------------- > > > > 1) Under "General setup," append "-kdump" to the current string in > > "Local version." > > > > 2) On x86, enable high memory support under "Processor type and > > features": > > > > CONFIG_HIGHMEM=y > > > > 3) On x86 and x86_64, disable symmetric multi-processing support > > under "Processor type and features": > > > > CONFIG_SMP=n > > > > 4) On ppc64, disable NUMA support and enable EMBEDDED support: > > > > CONFIG_NUMA=n > > CONFIG_EMBEDDED=y > > CONFIG_EEH=N for the dump-capture kernel > > Why are we disabling NUMA? AFAIK we work on more systems with NUMA than > without? > And why are we turning off EMBEDDED and EEH? > In some systems kdump with NUMA panics. Also EEH gives some oops while kdump booting. To disable EEH, we need to enable CONFIG_EMBEDDED > > 5) Enable "kernel crash dumps" support under "Processor type and > > features": > > > > CONFIG_CRASH_DUMP=y > > > > 6) Use a suitable value for "Physical address where the kernel is > > loaded" (under "Processor type and features"). This only appears when > > "kernel crash dumps" is enabled. By default this value is 0x1000000 > > (16MB). It should be the same as X in the "crashkernel=Y@X" boot > > parameter discussed above. > > > > On x86 and x86_64, use "CONFIG_PHYSICAL_START=0x1000000". > > > > On ppc64 the value is automatically set at 32MB when > > CONFIG_CRASH_DUMP is set. > > This whole step should start "On x86 ..." > > > 6) Optionally enable "/proc/vmcore support" under "Filesystems" -> > > "Pseudo filesystems". > > 6 + 1 = 6 :D > > > CONFIG_PROC_VMCORE=y > > > > 7) Make and install the kernel and its modules. DO NOT add this kernel > > to the boot loader configuration files. > > > > > > Load the Dump-capture Kernel > > ============================ > > > > After booting to the system kernel, load the dump-capture kernel using > > the following command: > > > > kexec -p \ > > --initrd= --args-linux \ > > --append="root= init 1 irqpoll" > > I've never tested irqpoll on powerpc, I'm not sure we want to recommend > it, has someone tested it? > > > Notes on loading the dump-capture kernel: > > > > * must be a vmlinux image (that is, an > > uncompressed ELF image). bzImage does not work at this time. > > > > * By default, the ELF headers are stored in ELF64 format to support > > systems with more than 4GB memory. The --elf32-core-headers option can > > be used to force the generation of ELF32 headers. This is necessary > > because GDB currently cannot open vmcore files with ELF64 headers on > > 32-bit systems. ELF32 headers can be used on non-PAE systems (that is, > > less than 4GB of memory). > > > > * The "irqpoll" boot parameter reduces driver initialization failures > > due to shared interrupts in the dump-capture kernel. > > > > * You must specify in the format corresponding to the root > > device name in the output of mount command. > > > * "init 1" boots the dump-capture kernel into single-user mode without > > networking. If you want networking, use "init 3." > > > > > > Kernel Panic > > ============ > > > > After successfully loading the dump-capture kernel as previously > > described, the system will reboot into the dump-capture kernel if a > > panic occurs. You can write a module to force the panic, or use > > "ALT-SysRq-c" to initiate a crash dump for testing purposes. > > > > > > Write Out the Dump File > > ======================= > > > > After the dump-capture kernel is booted, write out the dump file with > > the following command: > > > > cp /proc/vmcore > > > > You can also access dumped memory as a /dev/oldmem device for a linear > > and raw view. To create the device, use the following command: > > > > mknod /dev/oldmem c 1 12 > > > > Use the dd command with suitable options for count, bs, and skip to > > access specific portions of the dump. > > > > To see the entire memory, use the following command: > > > > dd if=/dev/oldmem of=oldmem.001 > > > > > > Analysis > > ======== > > > > Before analyzing the dump image, you should reboot into a stable kernel. > > > > You can do limited analysis using GDB on the dump file copied out of > > /proc/vmcore. Use the debug vmlinux built with -g and run the following > > command: > > > > gdb vmlinux > > > > Stack trace for the task on processor 0, register display, and memory > > display work fine. > > > > Note: GDB cannot analyze core files generated in ELF64 format for x86. > > On systems with a maximum of 4GB of memory, you can generate > > ELF32-format headers using the --elf32-core-headers kernel option on the > > dump kernel. > > > > You can also use the Crash utility to analyze dump files in Kdump > > format. Crash is available on Dave Anderson's site at the following URL: > > > > http://people.redhat.com/~anderson/ > > > > > > To Do > > ===== > > > > 1) Provide a kernel pages filtering mechanism, so core file size is not > > extreme on systems with huge memory banks. > > > > 2) Relocatable kernel can help in maintaining multiple kernels for > > crash_dump, and the same kernel as the system kernel can be used to > > capture the dump. > > > > > > Contact > > ======= > > > > Vivek Goyal (vgoyal@in.ibm.com) > > Maneesh Soni (maneesh@in.ibm.com) > > fastboot@lists.osdl.org > > > cheers > > -- > Michael Ellerman > IBM OzLabs > > wwweb: http://michael.ellerman.id.au > phone: +61 2 6212 1183 (tie line 70 21183) > > We do not inherit the earth from our ancestors, > we borrow it from our children. - S.M.A.R.T Person > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@ozlabs.org > https://ozlabs.org/mailman/listinfo/linuxppc-dev