Re: [PATCH] tracing: fix invalid function_graph entry

[Frederic Weisbecker <fweisbec@gmail.com>]

On Tue, Jul 28, 2009 at 08:11:24PM +0800, Lai Jiangshan wrote:
> 
> print_graph_entry() consumes current event, if this event
> is the last event in the page, the ring_buffer may reuse
> the page. It will become invalid.
> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---


Queued for .31, thanks Lai!


> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index abf7c4a..02102a3 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -835,9 +835,16 @@ print_graph_function(struct trace_iterator *iter)
>  
>  	switch (entry->type) {
>  	case TRACE_GRAPH_ENT: {
> -		struct ftrace_graph_ent_entry *field;
> +		/*
> +		 * print_graph_entry() may consume the current event,
> +		 * thus @field may become invalid, so we need to save it.
> +		 * sizeof(struct ftrace_graph_ent_entry) is very small,
> +		 * it is safely saved at the stack.
> +		 */
> +		struct ftrace_graph_ent_entry *field, saved;
>  		trace_assign_type(field, entry);
> -		return print_graph_entry(field, s, iter);
> +		saved = *field;
> +		return print_graph_entry(&saved, s, iter);
>  	}
>  	case TRACE_GRAPH_RET: {
>  		struct ftrace_graph_ret_entry *field;
>