On Mon, Sep 1, 2025 at 8:12 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>
>
> I do a PoC of adding bpf_in_interrupt() to bpf_experimental.h.
lgtm
> It works:
>
> extern bool CONFIG_PREEMPT_RT __kconfig __weak;
> #ifdef bpf_target_x86
what is bpf_target_x86 ?
> extern const int __preempt_count __ksym;
> #endif
>
> struct task_struct__preempt_rt {
> int softirq_disable_cnt;
> } __attribute__((preserve_access_index));
>
> /* Description
> * Report whether it is in interrupt context. Only works on x86.
arm64 shouldn't be hard to support either.
> */
> static inline int bpf_in_interrupt(void)
> {
> #ifdef bpf_target_x86
> int pcnt;
>
> pcnt = *(int *) bpf_this_cpu_ptr(&__preempt_count);
> if (!CONFIG_PREEMPT_RT) {
> return pcnt & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_MASK);
> } else {
> struct task_struct__preempt_rt *tsk;
>
> tsk = (void *) bpf_get_current_task_btf();
> return (pcnt & (NMI_MASK | HARDIRQ_MASK)) |
> (tsk->softirq_disable_cnt | SOFTIRQ_MASK);
> }
> #else
> return 0;
> #endif
> }
>
> However, I only test it for !PREEMPT_RT on x86.
>
> I'd like to respin the patchset by moving bpf_in_interrupt() to
> bpf_experimental.h.
I think the approach should work for PREEMPT_RT too.
Test it and send it.
imo this is better than a new kfunc.
Users can start using it right away without waiting for a new kernel.
