[PATCH] powerpc: Fix stack overflow crash in resume_kernel when ftracing

[Steven Rostedt]

On Thu, 2013-06-13 at 21:04 +1000, Michael Ellerman wrote:

> Although that should be sufficient to fix the bug, we also mark the
> runlatch routines as notrace. They are called very early in the
> exception entry and we are asking for trouble tracing them. They are
> also fairly uninteresting and tracing them just adds unnecessary
> overhead.

Note, I usually lean towards tracing everything that can be traced, and
only adding notrace to things that will actually cause a crash. If you
don't like them to be traced, you can always do:

echo '*__ppc64_runlatch_*'
> /sys/kernel/debug/tracing/set_ftrace_notrace

and that will keep them from being traced. You can also add it to the
kernel command line with: ftrace_notrace=*__ppc64_runlatch_* which will
also disable them on boot up.

Also trace-cmd has:

trace-cmd record -p function_graph -n '*__ppc64_runlatch_*'

that will do the same thing.

Hmm, I should add a way to disable things that are usually considered
noise. Perhaps add something like:


FTRACE_DEFAULT_OFF(__ppc64_runlatch_on);

That adds the function to a different section that places it into
another file that keeps it from being traced, but can be enabled when
you want it to.

-- Steve