Impact: build fix

Some architectures have not implemented save_stack_trace_tsk() yet:

  fs/built-in.o: In function `proc_pid_stack':
  base.c:(.text+0x3f140): undefined reference to `save_stack_trace_tsk'

So warn about that if the facility is used.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

fix:

ERROR: "print_stack_trace" [kernel/backtracetest.ko] undefined!
ERROR: "save_stack_trace" [kernel/backtracetest.ko] undefined!
Signed-off-by: NIngo Molnar <mingo@elte.hu>

and fix:

  Building modules, stage 2.
  MODPOST 376 modules
ERROR: "print_stack_trace" [kernel/backtracetest.ko] undefined!
make[1]: *** [__modpost] Error 1
Signed-off-by: NIngo Molnar <mingo@elte.hu>

- shorter code and better atomicity with regards to printk().

(It's been tested with the backtrace self-test code on i386 and x86_64.)

Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: NVegard Nossum <vegard.nossum@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This patch makes the stacktrace printout code \warn when the entries
pointer is unset rather than crashing when trying to access it in an
attempt to make it a bit more robust.

I was saving a stacktrace into an skb and forgot to copy it across skb
copies... I have since fixed the code, but it would have been easier
had the kernel not crashed in an interrupt.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Framework to generate and save stacktraces quickly, without printing anything
to the console.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>