[PATCH] kdump: Documentation for Kdump

This patch contains the documentation for the kexec based crash dump tool.

Quick kdump-howto
================================================================

1) Download and build kexec-tools.

2) Download and build the latest kexec/kdump (-mm) kernel patchset.
   Two kernels need to be built in order to get this feature working.

  A) First kernel:
   a) Enable "kexec system call" feature:
	CONFIG_KEXEC=y
   b) Physical load address (use default):
	CONFIG_PHYSICAL_START=0x100000
   c) Enable "sysfs file system support":
	CONFIG_SYSFS=y
   d) Boot into first kernel with the command line parameter "crashkernel=Y@X":
      For example: "crashkernel=64M@16M".

  B) Second kernel:
   a) Enable "kernel crash dumps" feature:
	CONFIG_CRASH_DUMP=y
   b) Physical load addreess, use same load address as X in "crashkernel"
      kernel parameter in 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

3) Boot into the first kernel.

4) Load the second kernel to be booted using:

   kexec -p <second-kernel> --crash-dump --args-linux --append="root=<root-dev>
   maxcpus=1 init 1"

5) System reboots into the second kernel when a panic occurs. A module can be
   written to force the panic, for testing purposes.

6) See Documentation/kdump.txt for how to read the first kernel's
   memory image and how to analyze it.

Signed-off-by: Hariprasad Nellitheertha <hari@in.ibm.com>
Signed-off-by: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: randy_dunlap <rdunlap@xenotime.net>
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>

1 files changed, 179 insertions, 0 deletions

diff --git a/Documentation/kdump/gdbmacros.txt b/Documentation/kdump/gdbmacros.txt
new file mode 100644
index 000000000000..bc1b9eb92ae1
--- /dev/null
+++ b/Documentation/kdump/gdbmacros.txt
@@ -0,0 +1,179 @@
+#
+# This file contains a few gdb macros (user defined commands) to extract
+# useful information from kernel crashdump (kdump) like stack traces of
+# all the processes or a particular process and trapinfo.
+#
+# These macros can be used by copying this file in .gdbinit (put in home
+# directory or current directory) or by invoking gdb command with
+# --command=<command-file-name> option
+#
+# Credits:
+# Alexander Nyberg <alexn@telia.com>
+# V Srivatsa <vatsa@in.ibm.com>
+# Maneesh Soni <maneesh@in.ibm.com>
+#
+
+define bttnobp
+        set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
+        set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
+        set $init_t=&init_task
+        set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
+        while ($next_t != $init_t)
+                set $next_t=(struct task_struct *)$next_t
+                printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
+                printf "===================\n"
+                set var $stackp = $next_t.thread.esp
+                set var $stack_top = ($stackp & ~4095) + 4096
+
+                while ($stackp < $stack_top)
+                        if (*($stackp) > _stext && *($stackp) < _sinittext)
+                                info symbol *($stackp)
+                        end
+                        set $stackp += 4
+                end
+                set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
+                while ($next_th != $next_t)
+                        set $next_th=(struct task_struct *)$next_th
+                        printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
+                        printf "===================\n"
+                        set var $stackp = $next_t.thread.esp
+                        set var $stack_top = ($stackp & ~4095) + 4096
+
+                        while ($stackp < $stack_top)
+                                if (*($stackp) > _stext && *($stackp) < _sinittext)
+                                        info symbol *($stackp)
+                                end
+                                set $stackp += 4
+                        end
+                        set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
+                end
+                set $next_t=(char *)($next_t->tasks.next) - $tasks_off
+        end
+end
+document bttnobp
+        dump all thread stack traces on a kernel compiled with !CONFIG_FRAME_POINTER
+end
+
+define btt
+        set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
+        set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
+        set $init_t=&init_task
+        set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
+        while ($next_t != $init_t)
+                set $next_t=(struct task_struct *)$next_t
+                printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
+                printf "===================\n"
+                set var $stackp = $next_t.thread.esp
+                set var $stack_top = ($stackp & ~4095) + 4096
+                set var $stack_bot = ($stackp & ~4095)
+
+                set $stackp = *($stackp)
+                while (($stackp < $stack_top) && ($stackp > $stack_bot))
+                        set var $addr = *($stackp + 4)
+                        info symbol $addr
+                        set $stackp = *($stackp)
+                end
+
+                set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
+                while ($next_th != $next_t)
+                        set $next_th=(struct task_struct *)$next_th
+                        printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
+                        printf "===================\n"
+                        set var $stackp = $next_t.thread.esp
+                        set var $stack_top = ($stackp & ~4095) + 4096
+                        set var $stack_bot = ($stackp & ~4095)
+
+                        set $stackp = *($stackp)
+                        while (($stackp < $stack_top) && ($stackp > $stack_bot))
+                                set var $addr = *($stackp + 4)
+                                info symbol $addr
+                                set $stackp = *($stackp)
+                        end
+                        set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
+                end
+                set $next_t=(char *)($next_t->tasks.next) - $tasks_off
+        end
+end
+document btt
+        dump all thread stack traces on a kernel compiled with CONFIG_FRAME_POINTER
+end
+
+define btpid
+        set var $pid = $arg0
+        set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
+        set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
+        set $init_t=&init_task
+        set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
+        set var $pid_task = 0
+
+        while ($next_t != $init_t)
+                set $next_t=(struct task_struct *)$next_t
+
+                if ($next_t.pid == $pid)
+                        set $pid_task = $next_t
+                end
+
+                set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
+                while ($next_th != $next_t)
+                        set $next_th=(struct task_struct *)$next_th
+                        if ($next_th.pid == $pid)
+                                set $pid_task = $next_th
+                        end
+                        set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
+                end
+                set $next_t=(char *)($next_t->tasks.next) - $tasks_off
+        end
+
+        printf "\npid %d; comm %s:\n", $pid_task.pid, $pid_task.comm
+        printf "===================\n"
+        set var $stackp = $pid_task.thread.esp
+        set var $stack_top = ($stackp & ~4095) + 4096
+        set var $stack_bot = ($stackp & ~4095)
+
+        set $stackp = *($stackp)
+        while (($stackp < $stack_top) && ($stackp > $stack_bot))
+                set var $addr = *($stackp + 4)
+                info symbol $addr
+                set $stackp = *($stackp)
+        end
+end
+document btpid
+        backtrace of pid
+end
+
+
+define trapinfo
+        set var $pid = $arg0
+        set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
+        set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
+        set $init_t=&init_task
+        set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
+        set var $pid_task = 0
+
+        while ($next_t != $init_t)
+                set $next_t=(struct task_struct *)$next_t
+
+                if ($next_t.pid == $pid)
+                        set $pid_task = $next_t
+                end
+
+                set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
+                while ($next_th != $next_t)
+                        set $next_th=(struct task_struct *)$next_th
+                        if ($next_th.pid == $pid)
+                                set $pid_task = $next_th
+                        end
+                        set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
+                end
+                set $next_t=(char *)($next_t->tasks.next) - $tasks_off
+        end
+
+        printf "Trapno %ld, cr2 0x%lx, error_code %ld\n", $pid_task.thread.trap_no, \
+                                $pid_task.thread.cr2, $pid_task.thread.error_code
+
+end
+document trapinfo
+        Run info threads and lookup pid of thread #1
+        'trapinfo <pid>' will tell you by which trap & possibly
+        addresthe kernel paniced.
+end