Filtering pid_tgid is meanlingless when the current task is preempted by an interrupt. To address this, introduce 'bpf_in_interrupt()' helper function, which allows BPF programs to determine whether they are executing in interrupt context. 'get_preempt_count()': * On x86, '*(int *) bpf_this_cpu_ptr(&__preempt_count)'. * On arm64, 'bpf_get_current_task_btf()->thread_info.preempt.count'. Then 'bpf_in_interrupt()' will be: * If !PREEMPT_RT, 'get_preempt_count() & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_MASK)'. * If PREEMPT_RT, '(get_preempt_count() & (NMI_MASK | HARDIRQ_MASK)) | (bpf_get_current_task_btf()->softirq_disable_cnt & SOFTIRQ_MASK)'. 'bpf_in_interrupt()' runs well when PREEMPT_RT is enabled. But it's difficult for me to test it well because I'm not familiar with PREEMPT_RT. Changes: v2 -> v3: * Address comments from Alexei: * Move bpf_in_interrupt() to bpf_experimental.h. * Add support for arm64. v2: https://lore.kernel.org/bpf/20250825131502.54269-1-leon.hwang@xxxxxxxxx/ v1 -> v2: * Fix a build error reported by test bot. Leon Hwang (2): selftests/bpf: Introduce experimental bpf_in_interrupt() selftests/bpf: Add case to test bpf_in_interrupt() .../testing/selftests/bpf/bpf_experimental.h | 54 +++++++++++++++++++ .../testing/selftests/bpf/prog_tests/timer.c | 30 +++++++++++ .../selftests/bpf/progs/timer_interrupt.c | 48 +++++++++++++++++ 3 files changed, 132 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/timer_interrupt.c -- 2.51.0
