tracing: Add critical section event support

These patches add critical section event tracing support.

Changes since RFC [1] are:
- Make critical events independent of the preempt/irqsoff tracer.
- Store pointers instead of symbol names to do less in the fast path.
- Other changes based on Steven's comments.

Here's an example of how Android's systrace will be using it to show critical sections as a gantt chart: http://imgur.com/download/TZplEVp

[1] https://patchwork.kernel.org/patch/9676579/

Joel Fernandes (2):
tracing: irqsoff: Move code under tracer config options
tracing: Add support for critical section events

 include/linux/ftrace.h          |   2 +-
 include/linux/irqflags.h        |   3 +-
 include/trace/events/critical.h |  45 ++++++
 kernel/trace/Kconfig            |   5 +
 kernel/trace/Makefile           |   1 +
 kernel/trace/trace_irqsoff.c    | 331 ++++++++++++++++++++++++++--------------
 6 files changed, 269 insertions(+), 118 deletions(-)
 create mode 100644 include/trace/events/critical.h

2.14.1.581.gf28d330327-goog