Recent issues with user space callchains processing within
page fault handler tracing showed as Peter said 'there's
just too much fail surface'.

The user space stack dump is just another source of the this issue.

Related list discussions:
  http://marc.info/?t=139302086500001&r=1&w=2
  http://marc.info/?t=139301437300003&r=1&w=2Suggested-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NJiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1393775800-13524-3-git-send-email-jolsa@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>