linux-kernel - Re: [PATCH v2] tracing: Ignore mmiotrace from kernel commandline

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Date:   Fri, 8 Sep 2017 11:08:38 -0400 (EDT)
From:   "Ziqian SUN (Zamir)" <zsun@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        karolherbst@...il.com, ppaalanen@...il.com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH v2] tracing: Ignore mmiotrace from kernel commandline

> On Wed, 30 Aug 2017 12:19:30 +0800
> "Ziqian SUN (Zamir)" <zsun@...hat.com> wrote:
> 
> > From: "Ziqian SUN (Zamir)" <zsun@...hat.com>
> > 
> > The mmiotrace tracer cannot be enabled with ftrace=mmiotrace in
> > kernel commandline. With this patch, a trace_noboot_tracer_list
> > is implemented and will be checked during system boot. If the
> > tracer declares itself as not for boot up, system will print out
> > a message and continue booting.
> > 
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=196557
> > Signed-off-by: Ziqian SUN (Zamir) <zsun@...hat.com>
> > ---
> >  kernel/trace/trace.c           | 34 +++++++++++++++++++++++++++++++++-
> >  kernel/trace/trace.h           | 11 +++++++++++
> >  kernel/trace/trace_mmiotrace.c |  4 ++++
> >  3 files changed, 48 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 44004d8..0d25b1e 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -319,6 +319,33 @@ void trace_free_pid_list(struct trace_pid_list
> > *pid_list)
> >  	kfree(pid_list);
> >  }
> >  
> > +struct mutex trace_noboot_tracer_lock;
> > +
> > +DEFINE_MUTEX(trace_noboot_tracer_lock);
> > +LIST_HEAD(trace_noboot_tracer_list);
> > +
> > +void trace_noboot_tracer_put(struct tracer_noboot *noboot_tracer)
> > +{
> > +	mutex_lock(&trace_noboot_tracer_lock);
> > +	list_add(&noboot_tracer->list, &trace_noboot_tracer_list);
> > +	mutex_unlock(&trace_noboot_tracer_lock);
> > +}
> > +
> > +bool trace_noboot_tracer_find(const char *str)
> > +{
> > +	mutex_lock(&trace_noboot_tracer_lock);
> > +	struct tracer_noboot *ptr = NULL;
> > +
> > +	list_for_each_entry(ptr, &trace_noboot_tracer_list, list) {
> > +		if (strcmp(ptr->name, str) == 0) {
> > +			mutex_unlock(&trace_noboot_tracer_lock);
> > +			return true;
> > +		}
> > +	}
> > +	mutex_unlock(&trace_noboot_tracer_lock);
> > +	return false;
> > +}
> > +
> >  /**
> >   * trace_find_filtered_pid - check if a pid exists in a filtered_pid list
> >   * @filtered_pids: The list of pids to check
> > @@ -1641,8 +1668,13 @@ int __init register_tracer(struct tracer *type)
> >  	if (strncmp(default_bootup_tracer, type->name, MAX_TRACER_SIZE))
> >  		goto out_unlock;
> >  
> > +	/* If the tracer should not be enabled by kernel parameter */
> > +	if (trace_noboot_tracer_find(type->name)) {
> > +		pr_warn("Tracer '%s' cannot be enabled during boot\n", type->name);
> > +		goto out_unlock;
> > +	}
> > +
> >  	printk(KERN_INFO "Starting tracer '%s'\n", type->name);
> > -	/* Do we want this tracer to start on bootup? */
> >  	tracing_set_tracer(&global_trace, type->name);
> >  	default_bootup_tracer = NULL;
> >  
> > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > index 490ba22..23bc668 100644
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -502,6 +502,17 @@ enum {
> >  	TRACE_IRQ_BIT,
> >  };
> >  
> > +/*
> > + * For tracer that cannot be enabled during boot time.
> > + */
> > +
> > +struct tracer_noboot {
> > +	const char		*name;
> > +	struct list_head	list;
> > +};
> > +
> > +void trace_noboot_tracer_put(struct tracer_noboot *noboot_tracer);
> > +
> >  #define trace_recursion_set(bit)	do { (current)->trace_recursion |=
> >  (1<<(bit)); } while (0)
> >  #define trace_recursion_clear(bit)	do { (current)->trace_recursion &=
> >  ~(1<<(bit)); } while (0)
> >  #define trace_recursion_test(bit)	((current)->trace_recursion &
> >  (1<<(bit)))
> > diff --git a/kernel/trace/trace_mmiotrace.c
> > b/kernel/trace/trace_mmiotrace.c
> > index cd7480d..06aa0a5 100644
> > --- a/kernel/trace/trace_mmiotrace.c
> > +++ b/kernel/trace/trace_mmiotrace.c
> > @@ -286,6 +286,10 @@ static enum print_line_t mmio_print_line(struct
> > trace_iterator *iter)
> >  
> >  __init static int init_mmio_trace(void)
> >  {
> > +	struct tracer_noboot mmio_notrace;
> > +
> > +	mmio_notrace.name = "mmiotrace";
> > +	trace_noboot_tracer_put(&mmio_notrace);
> >  	return register_tracer(&mmio_tracer);
> >  }
> >  device_initcall(init_mmio_trace);
> 
> This is way overkill. Just add
> 
> 	bool		noboot;
> 
> to struct tracer in trace.h and then to the mmiotracer:
> 
> struct tracer mmio_tracer = {
> 	[..]
> 	.noboot		= true,
> };
> 
> 
> And then in tracing_set_tracer() add after:
> 
> 	if (t == tr->current_trace)
> 		goto out;
> 
> this:
> 
> 	if (system_state < SYSTEM_RUNNING && t->noboot) {
> 		WARN(1, "Tracer %s not allowed on command line",
> 			t->name);
> 		goto out;
> 	}
> 
> That's it. No need for locking or anything else.
> 

Thanks for the suggestions. I will send a patch v3 after testing.

> -- Steve
> 
> 		
> 

-- 
Ziqian SUN