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,
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.
+ */
rcu_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
