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[PATCH] Kdump documentation update
Update the kdump documentation to reflect the changes due to recent kernel config option changes for kexec and kdump. Signed-off-by: Maneesh Soni <maneesh@in.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Maneesh Soni
Linus Torvalds
parent
05970d476f
commit
a7e670d828
@ -4,10 +4,10 @@ Documentation for kdump - the kexec-based crash dumping solution
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DESIGN
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======
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Kdump uses kexec to reboot to a second kernel whenever a dump needs to be taken.
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This second kernel is booted with very little memory. The first kernel reserves
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the section of memory that the second kernel uses. This ensures that on-going
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DMA from the first kernel does not corrupt the second kernel.
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Kdump uses kexec to reboot to a second kernel whenever a dump needs to be
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taken. This second kernel is booted with very little memory. The first kernel
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reserves the section of memory that the second kernel uses. This ensures that
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on-going DMA from the first kernel does not corrupt the second kernel.
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All the necessary information about Core image is encoded in ELF format and
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stored in reserved area of memory before crash. Physical address of start of
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@ -35,77 +35,82 @@ In the second kernel, "old memory" can be accessed in two ways.
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SETUP
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=====
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1) Download http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz
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and apply http://lse.sourceforge.net/kdump/patches/kexec-tools-1.101-kdump.patch
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and after that build the source.
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1) Download the upstream kexec-tools userspace package from
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http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz.
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2) Download and build the appropriate (2.6.13-rc1 onwards) vanilla kernel.
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Apply the latest consolidated kdump patch on top of kexec-tools-1.101
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from http://lse.sourceforge.net/kdump/. This arrangment has been made
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till all the userspace patches supporting kdump are integrated with
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upstream kexec-tools userspace.
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2) Download and build the appropriate (2.6.13-rc1 onwards) vanilla kernels.
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Two kernels need to be built in order to get this feature working.
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Following are the steps to properly configure the two kernels specific
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to kexec and kdump features:
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A) First kernel:
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A) First kernel or regular kernel:
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----------------------------------
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a) Enable "kexec system call" feature (in Processor type and features).
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CONFIG_KEXEC=y
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b) This kernel's physical load address should be the default value of
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0x100000 (0x100000, 1 MB) (in Processor type and features).
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CONFIG_PHYSICAL_START=0x100000
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c) Enable "sysfs file system support" (in Pseudo filesystems).
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CONFIG_SYSFS=y
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CONFIG_KEXEC=y
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b) Enable "sysfs file system support" (in Pseudo filesystems).
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CONFIG_SYSFS=y
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c) make
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d) Boot into first kernel with the command line parameter "crashkernel=Y@X".
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Use appropriate values for X and Y. Y denotes how much memory to reserve
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for the second kernel, and X denotes at what physical address the reserved
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memory section starts. For example: "crashkernel=64M@16M".
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for the second kernel, and X denotes at what physical address the
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reserved memory section starts. For example: "crashkernel=64M@16M".
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B) Second kernel:
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a) Enable "kernel crash dumps" feature (in Processor type and features).
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CONFIG_CRASH_DUMP=y
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b) Specify a suitable value for "Physical address where the kernel is
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loaded" (in Processor type and features). Typically this value
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should be same as X (See option d) above, e.g., 16 MB or 0x1000000.
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CONFIG_PHYSICAL_START=0x1000000
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c) Enable "/proc/vmcore support" (Optional, in Pseudo filesystems).
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CONFIG_PROC_VMCORE=y
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d) Disable SMP support and build a UP kernel (Until it is fixed).
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CONFIG_SMP=n
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e) Enable "Local APIC support on uniprocessors".
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CONFIG_X86_UP_APIC=y
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f) Enable "IO-APIC support on uniprocessors"
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CONFIG_X86_UP_IOAPIC=y
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Note: i) Options a) and b) depend upon "Configure standard kernel features
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(for small systems)" (under General setup).
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ii) Option a) also depends on CONFIG_HIGHMEM (under Processor
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type and features).
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iii) Both option a) and b) are under "Processor type and features".
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B) Second kernel or dump capture kernel:
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---------------------------------------
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a) For i386 architecture enable Highmem support
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CONFIG_HIGHMEM=y
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b) Enable "kernel crash dumps" feature (under "Processor type and features")
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CONFIG_CRASH_DUMP=y
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c) Make sure a suitable value for "Physical address where the kernel is
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loaded" (under "Processor type and features"). By default this value
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is 0x1000000 (16MB) and it should be same as X (See option d above),
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e.g., 16 MB or 0x1000000.
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CONFIG_PHYSICAL_START=0x1000000
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d) Enable "/proc/vmcore support" (Optional, under "Pseudo filesystems").
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CONFIG_PROC_VMCORE=y
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3) Boot into the first kernel. You are now ready to try out kexec-based crash
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dumps.
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4) Load the second kernel to be booted using:
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3) After booting to regular kernel or first kernel, load the second kernel
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using the following command:
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kexec -p <second-kernel> --args-linux --elf32-core-headers
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--append="root=<root-dev> init 1 irqpoll"
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--append="root=<root-dev> init 1 irqpoll maxcpus=1"
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Note: i) <second-kernel> has to be a vmlinux image. bzImage will not work,
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as of now.
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ii) By default ELF headers are stored in ELF64 format. Option
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--elf32-core-headers forces generation of ELF32 headers. gdb can
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not open ELF64 headers on 32 bit systems. So creating ELF32
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headers can come handy for users who have got non-PAE systems and
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hence have memory less than 4GB.
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iii) Specify "irqpoll" as command line parameter. This reduces driver
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initialization failures in second kernel due to shared interrupts.
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iv) <root-dev> needs to be specified in a format corresponding to
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the root device name in the output of mount command.
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v) If you have built the drivers required to mount root file
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system as modules in <second-kernel>, then, specify
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--initrd=<initrd-for-second-kernel>.
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Notes:
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======
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i) <second-kernel> has to be a vmlinux image ie uncompressed elf image.
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bzImage will not work, as of now.
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ii) --args-linux has to be speicfied as if kexec it loading an elf image,
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it needs to know that the arguments supplied are of linux type.
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iii) By default ELF headers are stored in ELF64 format to support systems
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with more than 4GB memory. Option --elf32-core-headers forces generation
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of ELF32 headers. The reason for this option being, as of now gdb can
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not open vmcore file with ELF64 headers on a 32 bit systems. So ELF32
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headers can be used if one has non-PAE systems and hence memory less
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than 4GB.
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iv) Specify "irqpoll" as command line parameter. This reduces driver
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initialization failures in second kernel due to shared interrupts.
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v) <root-dev> needs to be specified in a format corresponding to the root
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device name in the output of mount command.
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vi) If you have built the drivers required to mount root file system as
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modules in <second-kernel>, then, specify
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--initrd=<initrd-for-second-kernel>.
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vii) Specify maxcpus=1 as, if during first kernel run, if panic happens on
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non-boot cpus, second kernel doesn't seem to be boot up all the cpus.
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The other option is to always built the second kernel without SMP
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support ie CONFIG_SMP=n
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5) System reboots into the second kernel when a panic occurs. A module can be
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written to force the panic or "ALT-SysRq-c" can be used initiate a crash
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dump for testing purposes.
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4) After successfully loading the second kernel as above, if a panic occurs
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system reboots into the second kernel. A module can be written to force
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the panic or "ALT-SysRq-c" can be used initiate a crash dump for testing
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purposes.
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6) Write out the dump file using
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5) Once the second kernel has booted, write out the dump file using
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cp /proc/vmcore <dump-file>
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@ -119,9 +124,9 @@ SETUP
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Entire memory: dd if=/dev/oldmem of=oldmem.001
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ANALYSIS
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========
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Limited analysis can be done using gdb on the dump file copied out of
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/proc/vmcore. Use vmlinux built with -g and run
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@ -132,15 +137,19 @@ work fine.
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Note: gdb cannot analyse core files generated in ELF64 format for i386.
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Latest "crash" (crash-4.0-2.18) as available on Dave Anderson's site
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http://people.redhat.com/~anderson/ works well with kdump format.
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TODO
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====
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1) Provide a kernel pages filtering mechanism so that core file size is not
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insane on systems having huge memory banks.
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2) Modify "crash" tool to make it recognize this dump.
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2) Relocatable kernel can help in maintaining multiple kernels for crashdump
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and same kernel as the first kernel can be used to capture the dump.
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CONTACT
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=======
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Vivek Goyal (vgoyal@in.ibm.com)
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Maneesh Soni (maneesh@in.ibm.com)
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