RE: [PATCH bpf-next] rethook: Remove warning messages printed for finding return address of a frame.

[John Fastabend <john.fastabend@gmail.com>]

Kui-Feng Lee wrote:
> rethook_find_ret_addr() prints a warning message and returns 0 when the
> target task is running and not the "current" task to prevent returning an
> incorrect return address. However, this check is incomplete as the target
> task can still transition to the running state when finding the return
> address, although it is safe with RCU.
> 
> The issue we encounter is that the kernel frequently prints warning
> messages when BPF profiling programs call to bpf_get_task_stack() on
> running tasks.
> 
> The callers should be aware and willing to take the risk of receiving an
> incorrect return address from a task that is currently running other than
> the "current" one. A warning is not needed here as the callers are intent
> on it.
> 
> Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
> ---
>  kernel/trace/rethook.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> index fa03094e9e69..4297a132a7ae 100644
> --- a/kernel/trace/rethook.c
> +++ b/kernel/trace/rethook.c
> @@ -248,7 +248,7 @@ unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame
>  	if (WARN_ON_ONCE(!cur))
>  		return 0;
>  
> -	if (WARN_ON_ONCE(tsk != current && task_is_running(tsk)))
> +	if (tsk != current && task_is_running(tsk))
>  		return 0;
>  
>  	do {
> -- 
> 2.34.1
> 
> 

Acked-by: John Fastabend <john.fastabend@gmail.com>