Re: [PATCH] ftrace: fix ftrace_trace_task return value

[Steven Rostedt]

On Fri, 24 Jul 2020 20:50:48 -0400
Josef Bacik <josef@xxxxxxxxxxxxxx> wrote:

> I was attempting to use pid filtering with function_graph, but it wasn't
> allowing anything to make it through.  Turns out ftrace_trace_task
> returns false if ftrace_ignore_pid is not-empty, which isn't correct
> anymore.  We're now setting it to FTRACE_PID_IGNORE if we need to ignore
> that pid, otherwise it's set to the pid (which is weird considering the
> name) or to FTRACE_PID_TRACE.  Fix the check to check for !=
> FTRACE_PID_IGNORE.  With this we can now use function_graph with pid
> filtering.
> 

I just ran into this myself! And was about to go look at why function
graph pid filtering wasn't working. Thanks for the patch! I'll start
testing it this week.

-- Steve


> Fixes: 717e3f5ebc82 ("ftrace: Make function trace pid filtering a bit more exact")
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> ---
>  kernel/trace/ftrace.c | 3 ---
>  kernel/trace/trace.h  | 7 ++++++-
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 1903b80db6eb..7d879fae3777 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -139,9 +139,6 @@ static inline void ftrace_ops_init(struct ftrace_ops *ops)
>  #endif
>  }
>  
> -#define FTRACE_PID_IGNORE	-1
> -#define FTRACE_PID_TRACE	-2
> -
>  static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip,
>  			    struct ftrace_ops *op, struct pt_regs *regs)
>  {
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 13db4000af3f..1531ec565cb5 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -1103,6 +1103,10 @@ print_graph_function_flags(struct trace_iterator *iter, u32 flags)
>  extern struct list_head ftrace_pids;
>  
>  #ifdef CONFIG_FUNCTION_TRACER
> +
> +#define FTRACE_PID_IGNORE	-1
> +#define FTRACE_PID_TRACE	-2
> +
>  struct ftrace_func_command {
>  	struct list_head	list;
>  	char			*name;
> @@ -1114,7 +1118,8 @@ struct ftrace_func_command {
>  extern bool ftrace_filter_param __initdata;
>  static inline int ftrace_trace_task(struct trace_array *tr)
>  {
> -	return !this_cpu_read(tr->array_buffer.data->ftrace_ignore_pid);
> +	return this_cpu_read(tr->array_buffer.data->ftrace_ignore_pid) !=
> +		FTRACE_PID_IGNORE;
>  }
>  extern int ftrace_is_dead(void);
>  int ftrace_create_function_files(struct trace_array *tr,