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tracing: Always show all tracer options in the options directory

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There are options that are unique to a specific tracer (like function and
function graph). Currently, these options are only visible in the options
directory when the tracer is enabled.

This has been a pain, especially for something like the func_stack_trace
option that if used inappropriately, could bring the system to a crawl. But
the only way to see it, is to enable the function tracer.

For example, if one had done:

 # cd /sys/kernel/tracing
 # echo __schedule > set_ftrace_filter
 # echo 1 > options/func_stack_trace
 # echo function > current_tracer

The __schedule call will be traced and a stack trace will also be recorded
there. Now when you were done, you may do...

 # echo nop > current_tracer
 # echo > set_ftrace_filter

But you forgot to disable the func_stack_trace. The only way to disable it
is to re-enable function tracing first. If you do not add a filter to
set_ftrace_filter and just do:

 # echo function > current_tracer

Now you would be performing a stack trace on *every* function! On some
systems, that causes a live lock. Others may take a few minutes to fix your
mistake.

Having the func_stack_trace option visible allows you to check it and
disable it before enabling the funtion tracer.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Red Hat)
2015-09-29 17:31:55 -04:00
committed by Steven Rostedt
parent 73dddbb57b
commit 41d9c0becc
2 changed files with 27 additions and 34 deletions
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8
kernel/trace/trace.h
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@@ -333,6 +333,13 @@ struct tracer_flags {
#define TRACER_OPT(s, b) .name = #s, .bit = b
struct trace_option_dentry {
struct tracer_opt *opt;
struct tracer_flags *flags;
struct trace_array *tr;
struct dentry *entry;
};
/**
* struct tracer - a specific tracer and its callbacks to interact with tracefs
* @name: the name chosen to select it on the available_tracers file
@@ -387,6 +394,7 @@ struct tracer {
u32 mask, int set);
struct tracer *next;
struct tracer_flags *flags;
struct trace_option_dentry *topts;
int enabled;
int ref;
bool print_max;