tree cd23315ad0fa6660df5cbcb19230d38847309549
parent 1505c0baa0a8e3dc311a90b25eb24cc46b0894ea
author Steven Rostedt <rostedt@goodmis.org> 1391802077 -0500
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1392328083 -0800

ftrace: Synchronize setting function_trace_op with ftrace_trace_function

commit 405e1d834807e51b2ebd3dea81cb51e53fb61504 upstream.

ftrace_trace_function is a variable that holds what function will be called
directly by the assembly code (mcount). If just a single function is
registered and it handles recursion itself, then the assembly will call that
function directly without any helper function. It also passes in the
ftrace_op that was registered with the callback. The ftrace_op to send is
stored in the function_trace_op variable.

The ftrace_trace_function and function_trace_op needs to be coordinated such
that the called callback wont be called with the wrong ftrace_op, otherwise
bad things can happen if it expected a different op. Luckily, there's no
callback that doesn't use the helper functions that requires this. But
there soon will be and this needs to be fixed.

Use a set_function_trace_op to store the ftrace_op to set the
function_trace_op to when it is safe to do so (during the update function
within the breakpoint or stop machine calls). Or if dynamic ftrace is not
being used (static tracing) then we have to do a bit more synchronization
when the ftrace_trace_function is set as that takes affect immediately
(as oppose to dynamic ftrace doing it with the modification of the trampoline).

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>