On 2/9/25 10:29, Alexei Starovoitov wrote:
> 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 ?
>
bpf_target_x86 is a macro defined in bpf_tracing.h:
#if defined(__TARGET_ARCH_x86)
#define bpf_target_x86
...
#if defined(__x86_64__)
#define 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.
>
No problem.
I'll add support for arm64.
>> */
>> 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.
Yes, it works for PREEMPT_RT too.
It is able to get retval of bpf_in_interrupt() by running a simple demo.
However, it's really difficult to add selftest case for PREEMPT_RT, as
I'm not familiar with PREEMPT_RT.
Thanks,
Leon
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