Re: [PATCH 4/9] ftrace: Add enable/disable ftrace_ops control interface

[Steven Rostedt <rostedt@goodmis.org>]

[ Added Peter Z ]

On Sun, 2011-11-27 at 19:04 +0100, Jiri Olsa wrote:
> Adding a way to temporarily enable/disable ftrace_ops.
> 
> When there is a ftrace_ops with FTRACE_OPS_FL_CONTROL flag
> registered, the ftrace_ops_list_func processing function
> is used as ftrace function in order to have all registered
> ftrace_ops under control.
> 
> Also using jump label not to introduce overhead to current
> ftrace_ops_list_func processing.
> 

Are jump labels safe in NMI context yet? If not, this will need to wait
till we make it so.

-- Steve

> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> ---
>  include/linux/ftrace.h |   12 ++++++++++++
>  kernel/trace/ftrace.c  |   39 +++++++++++++++++++++++++++++----------
>  2 files changed, 41 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 26eafce..28b59f1 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -35,12 +35,14 @@ enum {
>  	FTRACE_OPS_FL_ENABLED		= 1 << 0,
>  	FTRACE_OPS_FL_GLOBAL		= 1 << 1,
>  	FTRACE_OPS_FL_DYNAMIC		= 1 << 2,
> +	FTRACE_OPS_FL_CONTROL		= 1 << 3,
>  };
>  
>  struct ftrace_ops {
>  	ftrace_func_t			func;
>  	struct ftrace_ops		*next;
>  	unsigned long			flags;
> +	atomic_t			disabled;
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  	struct ftrace_hash		*notrace_hash;
>  	struct ftrace_hash		*filter_hash;
> @@ -97,6 +99,16 @@ int register_ftrace_function(struct ftrace_ops *ops);
>  int unregister_ftrace_function(struct ftrace_ops *ops);
>  void clear_ftrace_function(void);
>  
> +static inline void enable_ftrace_function(struct ftrace_ops *ops)
> +{
> +	atomic_dec(&ops->disabled);
> +}
> +
> +static inline void disable_ftrace_function(struct ftrace_ops *ops)
> +{
> +	atomic_inc(&ops->disabled);
> +}
> +
>  extern void ftrace_stub(unsigned long a0, unsigned long a1);
>  
>  #else /* !CONFIG_FUNCTION_TRACER */
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 0ca0c0d..e5a9498 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -30,6 +30,7 @@
>  #include <linux/list.h>
>  #include <linux/hash.h>
>  #include <linux/rcupdate.h>
> +#include <linux/jump_label.h>
>  
>  #include <trace/events/sched.h>
>  
> @@ -94,6 +95,8 @@ ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;
>  ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;
>  static struct ftrace_ops global_ops;
>  
> +static struct jump_label_key ftrace_ops_control;
> +
>  static void
>  ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip);
>  
> @@ -196,17 +199,21 @@ static void update_ftrace_function(void)
>  
>  	update_global_ops();
>  
> -	/*
> -	 * If we are at the end of the list and this ops is
> -	 * not dynamic, then have the mcount trampoline call
> -	 * the function directly
> -	 */
> -	if (ftrace_ops_list == &ftrace_list_end ||
> -	    (ftrace_ops_list->next == &ftrace_list_end &&
> -	     !(ftrace_ops_list->flags & FTRACE_OPS_FL_DYNAMIC)))
> -		func = ftrace_ops_list->func;
> -	else
> +	if (jump_label_enabled(&ftrace_ops_control))
>  		func = ftrace_ops_list_func;
> +	else {
> +		/*
> +		 * If we are at the end of the list and this ops is
> +		 * not dynamic, then have the mcount trampoline call
> +		 * the function directly
> +		 */
> +		if (ftrace_ops_list == &ftrace_list_end ||
> +		    (ftrace_ops_list->next == &ftrace_list_end &&
> +		     !(ftrace_ops_list->flags & FTRACE_OPS_FL_DYNAMIC)))
> +			func = ftrace_ops_list->func;
> +		else
> +			func = ftrace_ops_list_func;
> +	}
>  
>  #ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
>  	ftrace_trace_function = func;
> @@ -280,6 +287,9 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
>  	} else
>  		add_ftrace_ops(&ftrace_ops_list, ops);
>  
> +	if (ops->flags & FTRACE_OPS_FL_CONTROL)
> +		jump_label_inc(&ftrace_ops_control);
> +
>  	if (ftrace_enabled)
>  		update_ftrace_function();
>  
> @@ -311,6 +321,9 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
>  	if (ret < 0)
>  		return ret;
>  
> +	if (ops->flags & FTRACE_OPS_FL_CONTROL)
> +		jump_label_dec(&ftrace_ops_control);
> +
>  	if (ftrace_enabled)
>  		update_ftrace_function();
>  
> @@ -3577,8 +3590,14 @@ ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip)
>  	preempt_disable_notrace();
>  	op = rcu_dereference_raw(ftrace_ops_list);
>  	while (op != &ftrace_list_end) {
> +		if (static_branch(&ftrace_ops_control))
> +			if ((op->flags & FTRACE_OPS_FL_CONTROL) &&
> +			    atomic_read(&op->disabled))
> +				goto next;
> +
>  		if (ftrace_ops_test(op, ip))
>  			op->func(ip, parent_ip);
> + next:
>  		op = rcu_dereference_raw(op->next);
>  	};
>  	preempt_enable_notrace();