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Diffstat (limited to 'Documentation/kdump')
| -rw-r--r-- | Documentation/kdump/gdbmacros.txt | 24 | ||||
| -rw-r--r-- | Documentation/kdump/kdump.txt | 553 |
2 files changed, 454 insertions, 123 deletions
diff --git a/Documentation/kdump/gdbmacros.txt b/Documentation/kdump/gdbmacros.txt index bc1b9eb92ae..9b9b454b048 100644 --- a/Documentation/kdump/gdbmacros.txt +++ b/Documentation/kdump/gdbmacros.txt @@ -175,5 +175,27 @@ end document trapinfo Run info threads and lookup pid of thread #1 'trapinfo <pid>' will tell you by which trap & possibly - addresthe kernel paniced. + address the kernel panicked. +end + + +define dmesg + set $i = 0 + set $end_idx = (log_end - 1) & (log_buf_len - 1) + + while ($i < logged_chars) + set $idx = (log_end - 1 - logged_chars + $i) & (log_buf_len - 1) + + if ($idx + 100 <= $end_idx) || \ + ($end_idx <= $idx && $idx + 100 < log_buf_len) + printf "%.100s", &log_buf[$idx] + set $i = $i + 100 + else + printf "%c", log_buf[$idx] + set $i = $i + 1 + end + end +end +document dmesg + print the kernel ring buffer end diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt index 7ff213f4bec..88d5a863712 100644 --- a/Documentation/kdump/kdump.txt +++ b/Documentation/kdump/kdump.txt @@ -1,141 +1,450 @@ -Documentation for kdump - the kexec-based crash dumping solution +================================================================ +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 http://www.xmission.com/~ebiederm/files/kexec/kexec-tools-1.101.tar.gz - and apply http://lse.sourceforge.net/kdump/patches/kexec-tools-1.101-kdump.patch - and after that build the source. - -2) Download and build the appropriate (latest) kexec/kdump (-mm) kernel - patchset and apply it to the vanilla kernel tree. - - Two kernels need to be built in order to get this feature working. - - A) First kernel: - a) Enable "kexec system call" feature (in Processor type and features). - CONFIG_KEXEC=y - b) This kernel's physical load address should be the default value of - 0x100000 (0x100000, 1 MB) (in Processor type and features). - CONFIG_PHYSICAL_START=0x100000 - c) Enable "sysfs file system support" (in Pseudo filesystems). - CONFIG_SYSFS=y - 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: - a) Enable "kernel crash dumps" feature (in Processor type and features). - CONFIG_CRASH_DUMP=y - b) Specify a suitable value for "Physical address where the kernel is - loaded" (in Processor type and features). Typically this value - should be same as X (See option d) above, e.g., 16 MB or 0x1000000. - CONFIG_PHYSICAL_START=0x1000000 - c) Enable "/proc/vmcore support" (Optional, in Pseudo filesystems). - CONFIG_PROC_VMCORE=y - d) Disable SMP support and build a UP kernel (Until it is fixed). - CONFIG_SMP=n - e) Enable "Local APIC support on uniprocessors". - CONFIG_X86_UP_APIC=y - f) Enable "IO-APIC support on uniprocessors" - CONFIG_X86_UP_IOAPIC=y - - Note: i) Options a) and b) depend upon "Configure standard kernel features - (for small systems)" (under General setup). - ii) Option a) also depends on CONFIG_HIGHMEM (under Processor - type and features). - iii) Both option a) and b) are under "Processor type and features". - -3) Boot into the first kernel. You are now ready to try out kexec-based crash - dumps. - -4) Load the second kernel to be booted using: - - kexec -p <second-kernel> --crash-dump --args-linux --append="root=<root-dev> - init 1 irqpoll" - - Note: i) <second-kernel> has to be a vmlinux image. bzImage will not work, - as of now. - ii) By default ELF headers are stored in ELF32 format (for i386). This - is sufficient to represent the physical memory up to 4GB. To store - headers in ELF64 format, specifiy "--elf64-core-headers" on the - kexec command line additionally. - iii) Specify "irqpoll" as command line parameter. This reduces driver - initialization failures in second kernel due to shared interrupts. - -5) System reboots into the second kernel when a panic occurs. A module can be - written to force the panic or "ALT-SysRq-c" can be used initiate a crash - dump for testing purposes. - -6) Write out the dump file using +This document includes overview, setup and installation, and analysis +information. - cp /proc/vmcore <dump-file> +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, +and s390x 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 and ia64 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 - Dump memory can also be accessed as a /dev/oldmem device for a linear/raw - view. To create the device, type: +5) Make and install the kernel and its modules. DO NOT add this kernel + to the boot loader configuration files. - mknod /dev/oldmem c 1 12 +Dump-capture kernel config options (Arch Dependent, ppc64) +---------------------------------------------------------- - Use "dd" with suitable options for count, bs and skip to access specific - portions of the dump. +1) Enable "Build a kdump crash kernel" support under "Kernel" options: - Entire memory: dd if=/dev/oldmem of=oldmem.001 + CONFIG_CRASH_DUMP=y -ANALYSIS +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. + + +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] + + 'start' is inclusive and 'end' is exclusive. + +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. + +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 + + +If you are using a 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>" + +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" + +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' 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. + +* 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 ======== -Limited analysis can be done using gdb on the dump file copied out of -/proc/vmcore. Use vmlinux built with -g and run +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> + gdb vmlinux <dump-file> -Stack trace for the task on processor 0, register display, memory display -work fine. +Stack trace for the task on processor 0, register display, and memory +display work fine. -Note: gdb cannot analyse core files generated in ELF64 format for i386. +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. -TODO -==== +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: -1) Provide a kernel pages filtering mechanism so that core file size is not - insane on systems having huge memory banks. -2) Modify "crash" tool to make it recognize this dump. + http://people.redhat.com/~anderson/ -CONTACT + +Contact ======= -Vivek Goyal (vgoyal@in.ibm.com) +Vivek Goyal (vgoyal@redhat.com) Maneesh Soni (maneesh@in.ibm.com) + |