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SubjectRe: [RFC patch 04/19] bpf/tracing: Remove redundant preempt_disable() in __bpf_trace_run()
On Fri, 14 Feb 2020 14:39:21 +0100
Thomas Gleixner <tglx@linutronix.de> 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@linutronix.de>
> ---
> 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();
> }
>

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