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Message-ID: <20090203092632.GB23466@nowhere>
Date: Tue, 3 Feb 2009 10:26:34 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
Arjan van de Ven <arjan@...radead.org>,
Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/3] trace: fix default boot up tracer
On Mon, Feb 02, 2009 at 09:38:32PM -0500, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
>
> Peter Zijlstra started the functionality to start up a default
> tracing at bootup. This patch finishes the work.
>
> Now if you add 'ftrace=<tracer>' to the command line, when that tracer
> is registered on bootup, that tracer is selected and starts tracing.
>
> Note, all selftests for tracers that are registered after this tracer
> is disabled. This prevents the selftests from disturbing the running
> tracer, or the running tracer from disturbing the selftest.
>
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
Great!
> ---
> kernel/trace/trace.c | 60 +++++++++++++++++++++++++++++++++++++++++++++-----
> 1 files changed, 54 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 2f8ac1f..2c720c7 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -53,6 +53,11 @@ unsigned long __read_mostly tracing_thresh;
> */
> static bool __read_mostly tracing_selftest_running;
>
> +/*
> + * If a tracer is running, we do not want to run SELFTEST.
> + */
> +static bool __read_mostly tracing_selftest_disabled;
> +
> /* For tracers that don't implement custom flags */
> static struct tracer_opt dummy_tracer_opt[] = {
> { }
> @@ -110,14 +115,19 @@ static cpumask_var_t __read_mostly tracing_buffer_mask;
> */
> int ftrace_dump_on_oops;
>
> -static int tracing_set_tracer(char *buf);
> +static int tracing_set_tracer(const char *buf);
> +
> +#define BOOTUP_TRACER_SIZE 100
> +static char bootup_tracer_buf[BOOTUP_TRACER_SIZE] __initdata;
> +static char *default_bootup_tracer;
>
> static int __init set_ftrace(char *str)
> {
> - tracing_set_tracer(str);
> + strncpy(bootup_tracer_buf, str, BOOTUP_TRACER_SIZE);
> + default_bootup_tracer = bootup_tracer_buf;
> return 1;
> }
> -__setup("ftrace", set_ftrace);
> +__setup("ftrace=", set_ftrace);
>
> static int __init set_ftrace_dump_on_oops(char *str)
> {
> @@ -468,7 +478,7 @@ int register_tracer(struct tracer *type)
> type->flags->opts = dummy_tracer_opt;
>
> #ifdef CONFIG_FTRACE_STARTUP_TEST
> - if (type->selftest) {
> + if (type->selftest && !tracing_selftest_disabled) {
> struct tracer *saved_tracer = current_trace;
> struct trace_array *tr = &global_trace;
> int i;
> @@ -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;
> }
>
> @@ -2245,7 +2272,7 @@ tracing_set_trace_read(struct file *filp, char __user *ubuf,
> return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
> }
>
> -static int tracing_set_tracer(char *buf)
> +static int tracing_set_tracer(const char *buf)
> {
> struct trace_array *tr = &global_trace;
> struct tracer *t;
> @@ -3163,5 +3190,26 @@ out_free_buffer_mask:
> out:
> return ret;
> }
> +
> +__init static int clear_boot_tracer(void)
> +{
> + /*
> + * The default tracer at boot buffer is an init section.
> + * This function is called in lateinit. If we did not
> + * find the boot tracer, then clear it out, to prevent
> + * later registration from accessing the buffer that is
> + * about to be freed.
> + */
> + if (!default_bootup_tracer)
> + return 0;
> +
> + printk(KERN_INFO "ftrace bootup tracer '%s' not registered.\n",
> + default_bootup_tracer);
> + default_bootup_tracer = NULL;
> +
> + return 0;
> +}
> +
> early_initcall(tracer_alloc_buffers);
> fs_initcall(tracer_init_debugfs);
> +late_initcall(clear_boot_tracer);
That makes me think that perhaps a tracer would prefer to keep or not the tracing
when system_state looses the value SYSTEM_BOOTING.
Something similar to earlyprintk by adding a "keep" value in the ftrace parameter.
Perhaps it's better to wait for someone to request it...
--
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