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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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