lkdtm: add debugfs access and loosen KPROBE ties

Add adds a debugfs interface and additional failure modes to LKDTM to
provide similar functionality to the provoke-crash driver submitted here:

  http://lwn.net/Articles/371208/

Crashes can now be induced either through module parameters (as before)
or through the debugfs interface as in provoke-crash.

The patch also provides a new "direct" interface, where KPROBES are not
used, i.e., the crash is invoked directly upon write to the debugfs
file. When built without KPROBES configured, only this mode is available.

Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
Cc: M. Mohan Kumar <mohan@in.ibm.com>
Cc: Americo Wang <xiyou.wangcong@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -864,8 +864,7 @@ config DEBUG_FORCE_WEAK_PER_CPU
 
 config LKDTM
 	tristate "Linux Kernel Dump Test Tool Module"
-	depends on DEBUG_KERNEL
-	depends on KPROBES
+	depends on DEBUG_FS
 	depends on BLOCK
 	default n
 	help
@@ -876,7 +875,7 @@ config LKDTM
 	called lkdtm.
 
 	Documentation on how to use the module can be found in
-	drivers/misc/lkdtm.c
+	Documentation/fault-injection/provoke-crashes.txt
 
 config FAULT_INJECTION
 	bool "Fault-injection framework"