[PATCH v3 bpf-next] bpf: Remove migrate_disable in kprobe_multi_link_prog_run

[Tao Chen]

Graph tracer framework ensures we won't migrate, 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 may will be reduced.
And add cant_sleep check for __this_cpu_inc_return.

Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
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

 v2 -> v3:
  - add cant_sleep for __this_cpu_inc_return.(Andrii)
  - shorten comments.(Andrii)
 v2: https://lore.kernel.org/bpf/20250805162732.1896687-1-chen.dylane@xxxxxxxxx

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 3ae52978cae..606007c387c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2728,20 +2728,25 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,
 	struct pt_regs *regs;
 	int err;
 
+	/*
+	 * graph tracer framework ensures we won't migrate, so there is no need
+	 * to use migrate_disable for bpf_prog_run again. The check here just for
+	 * __this_cpu_inc_return.
+	 */
+	cant_sleep();
+
 	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) {
 		bpf_prog_inc_misses_counter(link->link.prog);
 		err = 1;
 		goto out;
 	}
 
-	migrate_disable();
 	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