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SubjectRe: [PATCH 2/3] trace: fix default boot up tracer
On Mon, 02 Feb 2009 21:38:32 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:

> @@ -510,8 +520,25 @@ int register_tracer(struct tracer *type)
> out:
> tracing_selftest_running = false;
> mutex_unlock(&trace_types_lock);
> - lock_kernel();
>
> + if (!ret && default_bootup_tracer) {
> + if (!strncmp(default_bootup_tracer, type->name,
> + BOOTUP_TRACER_SIZE)) {
> + printk(KERN_INFO "Starting tracer '%s'\n",
> + type->name);
> + /* Do we want this tracer to start on bootup? */
> + tracing_set_tracer(type->name);
> + default_bootup_tracer = NULL;
> + /* disable other selftests, since this will break it. */
> + tracing_selftest_disabled = 1;
> +#ifdef CONFIG_FTRACE_STARTUP_TEST
> + printk(KERN_INFO "Disabling FTRACE selftests due"
> + " to running tracer '%s'\n", type->name);
> +#endif
> + }
> + }
> +
> + lock_kernel();
> return ret;
> }

The fun and games which register_tracer() plays with lock_kernel() tell
us that this function is only called at bootup time and hence could be
__init. A quick whizz through callers confirms that.

And if register_tracer() is also only callable at bootup, one suspects
that unregister_tracer() isn't useful. And lo, it has no callers.

This leads one to further surmise that trace_types_lock a) could be
__initdata and b) could be removed (the list is only altered when we're
running single-threaded). This appears to be the case.



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