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Subject: Re: [PATCH] tracing: Ignore mmiotrace from kernel commandline
To: rostedt@goodmis.org, linux-kernel@vger.kernel.org
Cc: mingo@redhat.com, karolherbst@gmail.com, ppaalanen@gmail.com,
        akpm@linux-foundation.org
References: <1504063543-18626-1-git-send-email-zsun@redhat.com>
From: "Ziqian SUN (Zamir)" <zsun@redhat.com>
Message-ID: <609ebee5-6d85-a919-3505-fd5273d62041@redhat.com>
Date: Wed, 30 Aug 2017 12:16:23 +0800
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On 08/30/2017 11:25 AM, Ziqian SUN (Zamir) wrote:
> From: "Ziqian SUN (Zamir)" <zsun@redhat.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@redhat.com>
> ---
>   kernel/trace/trace.c           | 35 ++++++++++++++++++++++++++++++++++-
>   kernel/trace/trace.h           | 11 +++++++++++
>   kernel/trace/trace_mmiotrace.c |  4 ++++
>   3 files changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 44004d8..aba774d 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -319,6 +319,34 @@ void trace_free_pid_list(struct trace_pid_list *pid_list)
>   	kfree(pid_list);
>   }
>   
> +/*struct list_head trace_noboot_tracer_list;*/
Just realized this commented line is no longer needed. I will send out 
v2 to remove it.
> +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 +1669,13 @@ 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);
> 

-- 
Ziqian SUN (Zamir)
Red Hat Software (Beijing) Co.,Ltd