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diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt deleted file mode 100644 index 3162eeb8c262..000000000000 --- a/Documentation/kdump/kdump.txt +++ /dev/null @@ -1,509 +0,0 @@ -================================================================ -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 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, ppc64, ia64, -s390x, arm and arm64 architectures. - -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. - -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. - -Similarly on PPC64 machines first 32KB of physical memory is needed for -booting regardless of where the kernel is loaded and to support 64K page -size kexec backs up the first 64KB memory. - -For s390x, when kdump is triggered, the crashkernel region is exchanged -with the region [0, crashkernel region size] and then the kdump kernel -runs in [0, crashkernel region size]. Therefore no relocatable kernel is -needed for s390x. - -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. Optionally the size of the ELF header can also be passed -when using the elfcorehdr=[size[KMG]@]offset[KMG] syntax. - - -With the dump-capture kernel, you can access the memory image 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 -------------------- - -1) Login as the root user. - -2) Download the kexec-tools user-space package from the following URL: - -http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz - -This is a symlink to the latest version. - -The latest kexec-tools git tree is available at: - -git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git -and -http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git - -There is also a gitweb interface available at -http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git - -More information about kexec-tools can be found at -http://horms.net/projects/kexec/ - -3) Unpack the tarball with the tar command, as follows: - - tar xvpzf kexec-tools.tar.gz - -4) Change to the kexec-tools directory, as follows: - - cd kexec-tools-VERSION - -5) Configure the package, as follows: - - ./configure - -6) Compile the package, as follows: - - make - -7) Install the package, as follows: - - make install - - -Build the system and dump-capture kernels ------------------------------------------ -There are two possible methods of using Kdump. - -1) Build a separate custom dump-capture kernel for capturing the - kernel core dump. - -2) Or use the system kernel binary itself as dump-capture kernel and there is - no need to build a separate dump-capture kernel. This is possible - only with the architectures which support a relocatable kernel. As - of today, i386, x86_64, ppc64, ia64, arm and arm64 architectures support - relocatable kernel. - -Building a relocatable kernel is advantageous from the point of view that -one does not have to build a second kernel for capturing the dump. But -at the same time one might want to build a custom dump capture kernel -suitable to his needs. - -Following are the configuration setting required for system and -dump-capture kernels for enabling kdump support. - -System kernel config options ----------------------------- - -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 - -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. - -Dump-capture kernel config options (Arch Independent) ------------------------------------------------------ - -1) Enable "kernel crash dumps" support under "Processor type and - features": - - CONFIG_CRASH_DUMP=y - -2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems". - - CONFIG_PROC_VMCORE=y - (CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.) - -Dump-capture kernel config options (Arch Dependent, i386 and x86_64) --------------------------------------------------------------------- - -1) On i386, enable high memory support under "Processor type and - features": - - CONFIG_HIGHMEM64G=y - or - CONFIG_HIGHMEM4G - -2) On i386 and x86_64, disable symmetric multi-processing support - under "Processor type and features": - - CONFIG_SMP=n - - (If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line - when loading the dump-capture kernel, see section "Load the Dump-capture - Kernel".) - -3) If one wants to build and use a relocatable kernel, - Enable "Build a relocatable kernel" support under "Processor type and - features" - - CONFIG_RELOCATABLE=y - -4) 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. A suitable value depends upon - whether kernel is relocatable or not. - - If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000 - This will compile the kernel for physical address 1MB, but given the fact - kernel is relocatable, it can be run from any physical address hence - kexec boot loader will load it in memory region reserved for dump-capture - kernel. - - Otherwise it should be the start of memory region reserved for - second kernel using boot parameter "crashkernel=Y@X". Here X is - start of memory region reserved for dump-capture kernel. - Generally X is 16MB (0x1000000). So you can set - CONFIG_PHYSICAL_START=0x1000000 - -5) Make and install the kernel and its modules. DO NOT add this kernel - to the boot loader configuration files. - -Dump-capture kernel config options (Arch Dependent, ppc64) ----------------------------------------------------------- - -1) Enable "Build a kdump crash kernel" support under "Kernel" options: - - CONFIG_CRASH_DUMP=y - -2) Enable "Build a relocatable kernel" support - - CONFIG_RELOCATABLE=y - - Make and install the kernel and its modules. - -Dump-capture kernel config options (Arch Dependent, ia64) ----------------------------------------------------------- - -- No specific options are required to create a dump-capture kernel - for ia64, other than those specified in the arch independent section - above. This means that it is possible to use the system kernel - as a dump-capture kernel if desired. - - The crashkernel region can be automatically placed by the system - kernel at run time. This is done by specifying the base address as 0, - or omitting it all together. - - crashkernel=256M@0 - or - crashkernel=256M - - If the start address is specified, note that the start address of the - kernel will be aligned to 64Mb, so if the start address is not then - any space below the alignment point will be wasted. - -Dump-capture kernel config options (Arch Dependent, arm) ----------------------------------------------------------- - -- To use a relocatable kernel, - Enable "AUTO_ZRELADDR" support under "Boot" options: - - AUTO_ZRELADDR=y - -Dump-capture kernel config options (Arch Dependent, arm64) ----------------------------------------------------------- - -- Please note that kvm of the dump-capture kernel will not be enabled - on non-VHE systems even if it is configured. This is because the CPU - will not be reset to EL2 on panic. - -Extended crashkernel syntax -=========================== - -While the "crashkernel=size[@offset]" syntax is sufficient for most -configurations, sometimes it's handy to have the reserved memory dependent -on the value of System RAM -- that's mostly for distributors that pre-setup -the kernel command line to avoid a unbootable system after some memory has -been removed from the machine. - -The syntax is: - - crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset] - range=start-[end] - -For example: - - crashkernel=512M-2G:64M,2G-:128M - -This would mean: - - 1) if the RAM is smaller than 512M, then don't reserve anything - (this is the "rescue" case) - 2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M - 3) if the RAM size is larger than 2G, then reserve 128M - - - -Boot into System Kernel -======================= - -1) Update the boot loader (such as grub, yaboot, or lilo) configuration - files as necessary. - -2) 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 (16MB) for the dump-capture kernel. - - On x86 and x86_64, use "crashkernel=64M@16M". - - On ppc64, use "crashkernel=128M@32M". - - On ia64, 256M@256M is a generous value that typically works. - The region may be automatically placed on ia64, see the - dump-capture kernel config option notes above. - If use sparse memory, the size should be rounded to GRANULE boundaries. - - On s390x, typically use "crashkernel=xxM". The value of xx is dependent - on the memory consumption of the kdump system. In general this is not - dependent on the memory size of the production system. - - On arm, the use of "crashkernel=Y@X" is no longer necessary; the - kernel will automatically locate the crash kernel image within the - first 512MB of RAM if X is not given. - - On arm64, use "crashkernel=Y[@X]". Note that the start address of - the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000). - -Load the Dump-capture Kernel -============================ - -After booting to the system kernel, dump-capture kernel needs to be -loaded. - -Based on the architecture and type of image (relocatable or not), one -can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz -of dump-capture kernel. Following is the summary. - -For i386 and x86_64: - - Use vmlinux if kernel is not relocatable. - - Use bzImage/vmlinuz if kernel is relocatable. -For ppc64: - - Use vmlinux -For ia64: - - Use vmlinux or vmlinuz.gz -For s390x: - - Use image or bzImage -For arm: - - Use zImage -For arm64: - - Use vmlinux or Image - -If you are using an uncompressed vmlinux image then use following command -to load dump-capture kernel. - - kexec -p <dump-capture-kernel-vmlinux-image> \ - --initrd=<initrd-for-dump-capture-kernel> --args-linux \ - --append="root=<root-dev> <arch-specific-options>" - -If you are using a compressed bzImage/vmlinuz, then use following command -to load dump-capture kernel. - - kexec -p <dump-capture-kernel-bzImage> \ - --initrd=<initrd-for-dump-capture-kernel> \ - --append="root=<root-dev> <arch-specific-options>" - -If you are using a compressed zImage, then use following command -to load dump-capture kernel. - - kexec --type zImage -p <dump-capture-kernel-bzImage> \ - --initrd=<initrd-for-dump-capture-kernel> \ - --dtb=<dtb-for-dump-capture-kernel> \ - --append="root=<root-dev> <arch-specific-options>" - -If you are using an uncompressed Image, then use following command -to load dump-capture kernel. - - kexec -p <dump-capture-kernel-Image> \ - --initrd=<initrd-for-dump-capture-kernel> \ - --append="root=<root-dev> <arch-specific-options>" - -Please note, that --args-linux does not need to be specified for ia64. -It is planned to make this a no-op on that architecture, but for now -it should be omitted - -Following are the arch specific command line options to be used while -loading dump-capture kernel. - -For i386, x86_64 and ia64: - "1 irqpoll maxcpus=1 reset_devices" - -For ppc64: - "1 maxcpus=1 noirqdistrib reset_devices" - -For s390x: - "1 maxcpus=1 cgroup_disable=memory" - -For arm: - "1 maxcpus=1 reset_devices" - -For arm64: - "1 maxcpus=1 reset_devices" - -Notes on loading the dump-capture kernel: - -* By default, the ELF headers are stored in ELF64 format to support - systems with more than 4GB memory. On i386, kexec automatically checks if - the physical RAM size exceeds the 4 GB limit and if not, uses ELF32. - So, on non-PAE systems, ELF32 is always used. - - 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. - -* 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. - -* Boot parameter "1" boots the dump-capture kernel into single-user - mode without networking. If you want networking, use "3". - -* We generally don't have to bring up a SMP kernel just to capture the - dump. Hence generally it is useful either to build a UP dump-capture - kernel or specify maxcpus=1 option while loading dump-capture kernel. - Note, though maxcpus always works, you had better replace it with - nr_cpus to save memory if supported by the current ARCH, such as x86. - -* You should enable multi-cpu support in dump-capture kernel if you intend - to use multi-thread programs with it, such as parallel dump feature of - makedumpfile. Otherwise, the multi-thread program may have a great - performance degradation. To enable multi-cpu support, you should bring up an - SMP dump-capture kernel and specify maxcpus/nr_cpus, disable_cpu_apicid=[X] - options while loading it. - -* For s390x there are two kdump modes: If a ELF header is specified with - the elfcorehdr= kernel parameter, it is used by the kdump kernel as it - is done on all other architectures. If no elfcorehdr= kernel parameter is - specified, the s390x kdump kernel dynamically creates the header. The - second mode has the advantage that for CPU and memory hotplug, kdump has - not to be reloaded with kexec_load(). - -* For s390x systems with many attached devices the "cio_ignore" kernel - parameter should be used for the kdump kernel in order to prevent allocation - of kernel memory for devices that are not relevant for kdump. The same - applies to systems that use SCSI/FCP devices. In that case the - "allow_lun_scan" zfcp module parameter should be set to zero before - setting FCP devices online. - -Kernel Panic -============ - -After successfully loading the dump-capture kernel as previously -described, the system will reboot into the dump-capture kernel if a -system crash is triggered. Trigger points are located in panic(), -die(), die_nmi() and in the sysrq handler (ALT-SysRq-c). - -The following conditions will execute a crash trigger point: - -If a hard lockup is detected and "NMI watchdog" is configured, the system -will boot into the dump-capture kernel ( die_nmi() ). - -If die() is called, and it happens to be a thread with pid 0 or 1, or die() -is called inside interrupt context or die() is called and panic_on_oops is set, -the system will boot into the dump-capture kernel. - -On powerpc systems when a soft-reset is generated, die() is called by all cpus -and the system will boot into the dump-capture kernel. - -For testing purposes, you can trigger a crash by using "ALT-SysRq-c", -"echo c > /proc/sysrq-trigger" or write a module to force the panic. - -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> - - -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/ - -Trigger Kdump on WARN() -======================= - -The kernel parameter, panic_on_warn, calls panic() in all WARN() paths. This -will cause a kdump to occur at the panic() call. In cases where a user wants -to specify this during runtime, /proc/sys/kernel/panic_on_warn can be set to 1 -to achieve the same behaviour. - -Contact -======= - -Vivek Goyal (vgoyal@redhat.com) -Maneesh Soni (maneesh@in.ibm.com) - |