proc_kstacks: Tool to print kernel traceback of all process'es threads

This is useful to do with e.g. wcfs when it is stuck somewhere in the
kernel and neither SIGABRT nor attaching via gdb work.

proc_kstacks

+#!/bin/bash -e
+# Program proc_kstacks dumps /proc/<prog>/tasks/stack
+
+die() {
+    echo "$*" >&2; exit 1
+}
+
+test "$#" = 1 || die "Usage: $0 <pid>"
+
+pid=$1
+echo "pid$pid  (`cat /proc/$pid/comm`)"
+
+task=/proc/$pid/task
+for tid in `cd $task && ls`; do
+    echo "T$tid"
+    cat $task/$tid/stack
+done