[Fastboot] Documentation feedback request.
Mohan Kumar M
mohan at in.ibm.com
Thu Apr 27 21:57:49 EST 2006
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 at 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 at 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 at 16M".
> >
> > On ppc64, use "crashkernel=128M at 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 at 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 <dump-capture-kernel> \
> > --initrd=<initrd-for-dump-capture-kernel> --args-linux \
> > --append="root=<root-dev> 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:
> >
> > * <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 <root-dev> 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 <dump-file>
> >
> > 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 <dump-file>
> >
> > 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 at in.ibm.com)
> > Maneesh Soni (maneesh at in.ibm.com)
>
> fastboot at 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 at ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-dev
More information about the Linuxppc-dev
mailing list