From: Tao Chen <chen.dylane@linux.dev>
Date: Thu, 14 Aug 2025 12:14:29 +0000 (+0800)
Subject: bpf: Remove migrate_disable in kprobe_multi_link_prog_run
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=abdaf49be5424db74e19d167c10d7dad79a0efc2;p=thirdparty%2Fkernel%2Fstable.git

bpf: Remove migrate_disable in kprobe_multi_link_prog_run

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@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250814121430.2347454-1-chen.dylane@linux.dev
---

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 3ae52978cae61..606007c387c52 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);