mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-11 08:06:39 +07:00
a7e670d828
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>
156 lines
6.5 KiB
Plaintext
156 lines
6.5 KiB
Plaintext
Documentation for kdump - the kexec-based crash dumping solution
|
|
================================================================
|
|
|
|
DESIGN
|
|
======
|
|
|
|
Kdump uses kexec to reboot to a second kernel whenever a dump needs to be
|
|
taken. This second kernel is booted with very little memory. The first kernel
|
|
reserves the section of memory that the second kernel uses. This ensures that
|
|
on-going DMA from the first kernel does not corrupt the second kernel.
|
|
|
|
All the necessary information about Core image is encoded in ELF format and
|
|
stored in reserved area of memory before crash. Physical address of start of
|
|
ELF header is passed to new kernel through command line parameter elfcorehdr=.
|
|
|
|
On i386, the first 640 KB of physical memory is needed to boot, irrespective
|
|
of where the kernel loads. Hence, this region is backed up by kexec just before
|
|
rebooting into the new kernel.
|
|
|
|
In the second kernel, "old memory" can be accessed in two ways.
|
|
|
|
- The first one is through a /dev/oldmem device interface. A capture utility
|
|
can read the device file and write out the memory in raw format. This is raw
|
|
dump of memory and analysis/capture tool should be intelligent enough to
|
|
determine where to look for the right information. ELF headers (elfcorehdr=)
|
|
can become handy here.
|
|
|
|
- The second interface is through /proc/vmcore. This exports the dump as an ELF
|
|
format file which can be written out using any file copy command
|
|
(cp, scp, etc). Further, gdb can be used to perform limited debugging on
|
|
the dump file. This method ensures methods ensure that there is correct
|
|
ordering of the dump pages (corresponding to the first 640 KB that has been
|
|
relocated).
|
|
|
|
SETUP
|
|
=====
|
|
|
|
1) Download the upstream kexec-tools userspace package from
|
|
http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz.
|
|
|
|
Apply the latest consolidated kdump patch on top of kexec-tools-1.101
|
|
from http://lse.sourceforge.net/kdump/. This arrangment has been made
|
|
till all the userspace patches supporting kdump are integrated with
|
|
upstream kexec-tools userspace.
|
|
|
|
2) Download and build the appropriate (2.6.13-rc1 onwards) vanilla kernels.
|
|
Two kernels need to be built in order to get this feature working.
|
|
Following are the steps to properly configure the two kernels specific
|
|
to kexec and kdump features:
|
|
|
|
A) First kernel or regular kernel:
|
|
----------------------------------
|
|
a) Enable "kexec system call" feature (in Processor type and features).
|
|
CONFIG_KEXEC=y
|
|
b) Enable "sysfs file system support" (in Pseudo filesystems).
|
|
CONFIG_SYSFS=y
|
|
c) make
|
|
d) Boot into first kernel with the command line parameter "crashkernel=Y@X".
|
|
Use appropriate values for X and Y. Y denotes how much memory to reserve
|
|
for the second kernel, and X denotes at what physical address the
|
|
reserved memory section starts. For example: "crashkernel=64M@16M".
|
|
|
|
|
|
B) Second kernel or dump capture kernel:
|
|
---------------------------------------
|
|
a) For i386 architecture enable Highmem support
|
|
CONFIG_HIGHMEM=y
|
|
b) Enable "kernel crash dumps" feature (under "Processor type and features")
|
|
CONFIG_CRASH_DUMP=y
|
|
c) Make sure a suitable value for "Physical address where the kernel is
|
|
loaded" (under "Processor type and features"). By default this value
|
|
is 0x1000000 (16MB) and it should be same as X (See option d above),
|
|
e.g., 16 MB or 0x1000000.
|
|
CONFIG_PHYSICAL_START=0x1000000
|
|
d) Enable "/proc/vmcore support" (Optional, under "Pseudo filesystems").
|
|
CONFIG_PROC_VMCORE=y
|
|
|
|
3) After booting to regular kernel or first kernel, load the second kernel
|
|
using the following command:
|
|
|
|
kexec -p <second-kernel> --args-linux --elf32-core-headers
|
|
--append="root=<root-dev> init 1 irqpoll maxcpus=1"
|
|
|
|
Notes:
|
|
======
|
|
i) <second-kernel> has to be a vmlinux image ie uncompressed elf image.
|
|
bzImage will not work, as of now.
|
|
ii) --args-linux has to be speicfied as if kexec it loading an elf image,
|
|
it needs to know that the arguments supplied are of linux type.
|
|
iii) By default ELF headers are stored in ELF64 format to support systems
|
|
with more than 4GB memory. Option --elf32-core-headers forces generation
|
|
of ELF32 headers. The reason for this option being, as of now gdb can
|
|
not open vmcore file with ELF64 headers on a 32 bit systems. So ELF32
|
|
headers can be used if one has non-PAE systems and hence memory less
|
|
than 4GB.
|
|
iv) Specify "irqpoll" as command line parameter. This reduces driver
|
|
initialization failures in second kernel due to shared interrupts.
|
|
v) <root-dev> needs to be specified in a format corresponding to the root
|
|
device name in the output of mount command.
|
|
vi) If you have built the drivers required to mount root file system as
|
|
modules in <second-kernel>, then, specify
|
|
--initrd=<initrd-for-second-kernel>.
|
|
vii) Specify maxcpus=1 as, if during first kernel run, if panic happens on
|
|
non-boot cpus, second kernel doesn't seem to be boot up all the cpus.
|
|
The other option is to always built the second kernel without SMP
|
|
support ie CONFIG_SMP=n
|
|
|
|
4) After successfully loading the second kernel as above, if a panic occurs
|
|
system reboots into the second kernel. A module can be written to force
|
|
the panic or "ALT-SysRq-c" can be used initiate a crash dump for testing
|
|
purposes.
|
|
|
|
5) Once the second kernel has booted, write out the dump file using
|
|
|
|
cp /proc/vmcore <dump-file>
|
|
|
|
Dump memory can also be accessed as a /dev/oldmem device for a linear/raw
|
|
view. To create the device, type:
|
|
|
|
mknod /dev/oldmem c 1 12
|
|
|
|
Use "dd" with suitable options for count, bs and skip to access specific
|
|
portions of the dump.
|
|
|
|
Entire memory: dd if=/dev/oldmem of=oldmem.001
|
|
|
|
|
|
ANALYSIS
|
|
========
|
|
Limited analysis can be done using gdb on the dump file copied out of
|
|
/proc/vmcore. Use vmlinux built with -g and run
|
|
|
|
gdb vmlinux <dump-file>
|
|
|
|
Stack trace for the task on processor 0, register display, memory display
|
|
work fine.
|
|
|
|
Note: gdb cannot analyse core files generated in ELF64 format for i386.
|
|
|
|
Latest "crash" (crash-4.0-2.18) as available on Dave Anderson's site
|
|
http://people.redhat.com/~anderson/ works well with kdump format.
|
|
|
|
|
|
TODO
|
|
====
|
|
1) Provide a kernel pages filtering mechanism so that core file size is not
|
|
insane on systems having huge memory banks.
|
|
2) Relocatable kernel can help in maintaining multiple kernels for crashdump
|
|
and same kernel as the first kernel can be used to capture the dump.
|
|
|
|
|
|
CONTACT
|
|
=======
|
|
Vivek Goyal (vgoyal@in.ibm.com)
|
|
Maneesh Soni (maneesh@in.ibm.com)
|