Re: [GIT pull] core/urgent for v5.4-rc7

[Joe Perches <joe@perches.com>]

On Sun, 2019-11-10 at 10:21 +0000, Thomas Gleixner wrote:
> A small fix for a stacktrace regression. Saving a stacktrace for a foreign
> task skipped an extra entry which makes e.g. the output of /proc/$PID/stack
> incomplete.
[]
> ------------------>
> Jiri Slaby (1):
>       stacktrace: Don't skip first entry on noncurrent tasks
[]
> diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
[]
> @@ -141,7 +141,8 @@ unsigned int stack_trace_save_tsk(struct task_struct *tsk, unsigned long *store,
>  	struct stacktrace_cookie c = {
>  		.store	= store,
>  		.size	= size,
> -		.skip	= skipnr + 1,
> +		/* skip this function if they are tracing us */
> +		.skip	= skipnr + !!(current == tsk),

trivia:

This idiom '!!(logical test)' is odd and redundant.
Logical test result is already 0 or 1, no !! is unnecessary.

>  	};
>  
>  	if (!try_get_task_stack(tsk))
> @@ -298,7 +299,8 @@ unsigned int stack_trace_save_tsk(struct task_struct *task,
>  	struct stack_trace trace = {
>  		.entries	= store,
>  		.max_entries	= size,
> -		.skip		= skipnr + 1,
> +		/* skip this function if they are tracing us */
> +		.skip	= skipnr + !!(current == task),
>  	};
>  
>  	save_stack_trace_tsk(task, &trace);
> 
>