Re: [RFC patch 04/19] bpf/tracing: Remove redundant preempt_disable() in __bpf_trace_run()

[Steven Rostedt]

On Fri, 14 Feb 2020 14:39:21 +0100
Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:

> __bpf_trace_run() disables preemption around the BPF_PROG_RUN() invocation.
> 
> This is redundant because __bpf_trace_run() is invoked from a trace point
> via __DO_TRACE() which already disables preemption _before_ invoking any of
> the functions which are attached to a trace point.
> 
> Remove it.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>  kernel/trace/bpf_trace.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1476,9 +1476,7 @@ static __always_inline
>  void __bpf_trace_run(struct bpf_prog *prog, u64 *args)
>  {

Should there be a "cant_migrate()" added here?

-- Steve

>  	rcu_read_lock();
> -	preempt_disable();
>  	(void) BPF_PROG_RUN(prog, args);
> -	preempt_enable();
>  	rcu_read_unlock();
>  }
>