在 2025/8/13 06:05, Andrii Nakryiko 写道:
On Tue, Aug 5, 2025 at 9:28 AM Tao Chen <chen.dylane@xxxxxxxxx> wrote:bpf program should run under migration disabled, kprobe_multi_link_prog_run called all the way from graph tracer, which disables preemption in function_graph_enter_regs, as Jiri and Yonghong suggested, there is no need to use migrate_disable. As a result, some overhead maybe will be reduced. Fixes: 0dcac2725406 ("bpf: Add multi kprobe link") Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx> Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx> Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx> --- kernel/trace/bpf_trace.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) Change list: v1 -> v2: - s/called the way/called all the way/.(Jiri) v1: https://lore.kernel.org/bpf/f7acfd22-bcf3-4dff-9a87-7c1e6f84ce9c@xxxxxxxxx diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 3ae52978cae..5701791e3cb 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -2734,14 +2734,19 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,even though bpf_prog_run() eventually calls cant_migrate(), we should add it before that __this_cpu_inc_return() call as well, because that one is relying on that non-migration independently from bpf_prog_run()
maybe cant_sleep() is better like trace_call_bpf, cant_sleep dose not check migration_disabled again, which is done in __this_cpu_preempt_check. I will add it in v3.
goto out; } - migrate_disable(); + /* + * bpf program should run under migration disabled, kprobe_multi_link_prog_run + * called all the way from graph tracer, which disables preemption in + * function_graph_enter_regs, so there is no need to use migrate_disable. + * Accessing the above percpu data bpf_prog_active is also safe for the same + * reason. + */let's shorten this a bit to something like: /* graph tracer framework ensures we won't migrate */ cant_migrate(); all the other stuff in the comment can become outdated way too easily and/or is sort of general BPF implementation knowledge pw-bot: crrcu_read_lock(); regs = ftrace_partial_regs(fregs, bpf_kprobe_multi_pt_regs_ptr()); old_run_ctx = bpf_set_run_ctx(&run_ctx.session_ctx.run_ctx); err = bpf_prog_run(link->link.prog, regs); bpf_reset_run_ctx(old_run_ctx); rcu_read_unlock(); - migrate_enable(); out: __this_cpu_dec(bpf_prog_active); -- 2.48.1
-- Best Regards Tao Chen
