From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [Fastboot] Documentation feedback request. From: Michael Ellerman To: David Wilder In-Reply-To: <444FB2AF.3020802@us.ibm.com> References: <444FB2AF.3020802@us.ibm.com> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-21zlVN4+iSfsWeMNNJSr" Date: Thu, 27 Apr 2006 09:44:31 +1000 Message-Id: <1146095071.29876.23.camel@localhost.localdomain> Mime-Version: 1.0 Cc: linuxppc-dev list , fastboot@lists.osdl.org Reply-To: michael@ellerman.id.au List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --=-21zlVN4+iSfsWeMNNJSr Content-Type: text/plain Content-Transfer-Encoding: quoted-printable 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=20 > comments. I will incorporate your feedback and send up to Linus. >=20 > plain text document attachment (kdump-final-20060425.txt) > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > Documentation for Kdump - The kexec-based Crash Dumping Solution > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >=20 > This document includes overview, setup and installation, and analysis > information. >=20 > Overview > =3D=3D=3D=3D=3D=3D=3D=3D >=20 > 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. >=20 > 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. >=20 > 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.=20 > 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. >=20 > 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=3D boot > parameter. >=20 > With the dump-capture kernel, you can access the memory image, or "old > memory," in two ways: >=20 > - 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. >=20 > - 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 ar= e > correctly ordered. >=20 >=20 > Setup and Installation > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >=20 > Install kexec-tools and the Kdump patch > --------------------------------------- >=20 > 1) Login as the root user. >=20 > 2) Download the kexec-tools user-space package from the following URL: >=20 > http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz >=20 > 3) Unpack the tarball with the tar command, as follows: >=20 > tar xvpzf kexec-tools-1.101.tar.gz >=20 > 4) Download the latest consolidated Kdump patch from the following URL: >=20 > http://lse.sourceforge.net/kdump/ > =20 > (This location is being used until all the user-space Kdump patches > are integrated with the kexec-tools package.) > =20 > 5) Change to the kexec-tools-1.101 directory, as follows: >=20 > cd kexec-tools-1.101 >=20 > 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.) > =20 > patch -p1 < /path-to-kdump-patch/kexec-tools-1.101-kdump.patch >=20 > 7) Configure the package, as follows: >=20 > ./configure >=20 > 8) Compile the package, as follows: >=20 > make >=20 > 9) Install the package, as follows: >=20 > make install >=20 >=20 > Download and build the system and dump-capture kernels > ------------------------------------------------------ >=20 > 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: >=20 > System kernel > ------------- >=20 > 1) Enable "kexec system call" in "Processor type and features." >=20 > CONFIG_KEXEC=3Dy >=20 > 2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo > filesystems." This is usually enabled by default. >=20 > CONFIG_SYSFS=3Dy >=20 > 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: >=20 > grep 'CONFIG_SYSFS' .config Is there a particular requirement for sysfs? > 3) Enable "Compile the kernel with debug info" in "Kernel hacking." >=20 > CONFIG_DEBUG_INFO=3DY >=20 > 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. > =20 > 4) Make and install the kernel and its modules. Update the boot loader > (such as grub, yaboot, or lilo) configuration files as necessary. >=20 > 5) Boot the system kernel with the boot parameter "crashkernel=3DY@X", > where Y specifies how much memory to reserve for the dump-capture kern= el > and X specifies the beginning of this reserved memory. For example, > "crashkernel=3D64M@16M" tells the system kernel to reserve 64 MB of me= mory > 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=3D64M@16M". >=20 > On ppc64, use "crashkernel=3D128M@32M". No just use "crashkernel=3D128M". > The dump-capture kernel > ----------------------- >=20 > 1) Under "General setup," append "-kdump" to the current string in > "Local version." >=20 > 2) On x86, enable high memory support under "Processor type and > features": >=20 > CONFIG_HIGHMEM=3Dy >=20 > 3) On x86 and x86_64, disable symmetric multi-processing support > under "Processor type and features": > =20 > CONFIG_SMP=3Dn >=20 > 4) On ppc64, disable NUMA support and enable EMBEDDED support: > =20 > CONFIG_NUMA=3Dn > CONFIG_EMBEDDED=3Dy > CONFIG_EEH=3DN 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? > 5) Enable "kernel crash dumps" support under "Processor type and > features": >=20 > CONFIG_CRASH_DUMP=3Dy >=20 > 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=3DY@X" boot > parameter discussed above. >=20 > On x86 and x86_64, use "CONFIG_PHYSICAL_START=3D0x1000000". > =20 > 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 =3D 6 :D > CONFIG_PROC_VMCORE=3Dy > =20 > 7) Make and install the kernel and its modules. DO NOT add this kernel > to the boot loader configuration files. > =20 >=20 > Load the Dump-capture Kernel > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D >=20 > After booting to the system kernel, load the dump-capture kernel using > the following command: >=20 > kexec -p \ > --initrd=3D --args-linux \ > --append=3D"root=3D 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: >=20 > * must be a vmlinux image (that is, an > uncompressed ELF image). bzImage does not work at this time. >=20 > * 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). > =20 > * The "irqpoll" boot parameter reduces driver initialization failures > due to shared interrupts in the dump-capture kernel. > =20 > * 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." >=20 >=20 > Kernel Panic > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >=20 > 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. >=20 >=20 > Write Out the Dump File > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >=20 > After the dump-capture kernel is booted, write out the dump file with > the following command: >=20 > cp /proc/vmcore >=20 > 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: >=20 > mknod /dev/oldmem c 1 12 >=20 > Use the dd command with suitable options for count, bs, and skip to > access specific portions of the dump. >=20 > To see the entire memory, use the following command: > =20 > dd if=3D/dev/oldmem of=3Doldmem.001 >=20 >=20 > Analysis > =3D=3D=3D=3D=3D=3D=3D=3D >=20 > Before analyzing the dump image, you should reboot into a stable kernel. >=20 > 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: >=20 > gdb vmlinux >=20 > Stack trace for the task on processor 0, register display, and memory > display work fine. >=20 > Note: GDB cannot analyze core files generated in ELF64 format for x86.=20 > 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. >=20 > 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: >=20 > http://people.redhat.com/~anderson/ >=20 >=20 > To Do > =3D=3D=3D=3D=3D >=20 > 1) Provide a kernel pages filtering mechanism, so core file size is not > extreme on systems with huge memory banks. >=20 > 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. >=20 >=20 > Contact > =3D=3D=3D=3D=3D=3D=3D >=20 > Vivek Goyal (vgoyal@in.ibm.com) > Maneesh Soni (maneesh@in.ibm.com) fastboot@lists.osdl.org cheers --=20 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 --=-21zlVN4+iSfsWeMNNJSr Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.2 (GNU/Linux) iD8DBQBEUAXfdSjSd0sB4dIRAqp+AKDHyCZAYGd1Yk3pW6RyhJr4B4GNGACgsqjl RSo4qo+ICX2Wzyp770m+K6g= =dixm -----END PGP SIGNATURE----- --=-21zlVN4+iSfsWeMNNJSr--