* [PATCH bpf-next] bpf: Remove migrate_disable in kprobe_multi_link_prog_run
@ 2025-08-05 12:23 Tao Chen
2025-08-05 15:48 ` Yonghong Song
2025-08-05 16:04 ` Jiri Olsa
0 siblings, 2 replies; 4+ messages in thread
From: Tao Chen @ 2025-08-05 12:23 UTC (permalink / raw)
To: song, jolsa, ast, daniel, andrii, martin.lau, eddyz87,
yonghong.song, john.fastabend, kpsingh, sdf, haoluo,
mattbobrowski, rostedt, mhiramat, mathieu.desnoyers
Cc: bpf, linux-kernel, linux-trace-kernel, Tao Chen
bpf program should run under migration disabled, kprobe_multi_link_prog_run
called 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")
Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
kernel/trace/bpf_trace.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 3ae52978cae..1993fc62539 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 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
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH bpf-next] bpf: Remove migrate_disable in kprobe_multi_link_prog_run
2025-08-05 12:23 [PATCH bpf-next] bpf: Remove migrate_disable in kprobe_multi_link_prog_run Tao Chen
@ 2025-08-05 15:48 ` Yonghong Song
2025-08-05 16:04 ` Jiri Olsa
1 sibling, 0 replies; 4+ messages in thread
From: Yonghong Song @ 2025-08-05 15:48 UTC (permalink / raw)
To: Tao Chen, song, jolsa, ast, daniel, andrii, martin.lau, eddyz87,
john.fastabend, kpsingh, sdf, haoluo, mattbobrowski, rostedt,
mhiramat, mathieu.desnoyers
Cc: bpf, linux-kernel, linux-trace-kernel
On 8/5/25 5:23 AM, Tao Chen wrote:
> bpf program should run under migration disabled, kprobe_multi_link_prog_run
> called 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")
> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH bpf-next] bpf: Remove migrate_disable in kprobe_multi_link_prog_run
2025-08-05 12:23 [PATCH bpf-next] bpf: Remove migrate_disable in kprobe_multi_link_prog_run Tao Chen
2025-08-05 15:48 ` Yonghong Song
@ 2025-08-05 16:04 ` Jiri Olsa
2025-08-05 16:17 ` Tao Chen
1 sibling, 1 reply; 4+ messages in thread
From: Jiri Olsa @ 2025-08-05 16:04 UTC (permalink / raw)
To: Tao Chen
Cc: song, ast, daniel, andrii, martin.lau, eddyz87, yonghong.song,
john.fastabend, kpsingh, sdf, haoluo, mattbobrowski, rostedt,
mhiramat, mathieu.desnoyers, bpf, linux-kernel,
linux-trace-kernel
On Tue, Aug 05, 2025 at 08:23:12PM +0800, Tao Chen wrote:
> bpf program should run under migration disabled, kprobe_multi_link_prog_run
> called 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")
> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
Acked-by: Jiri Olsa <jolsa@kernel.org>
thanks,
jirka
> ---
> kernel/trace/bpf_trace.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 3ae52978cae..1993fc62539 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 the way from graph tracer, which disables preemption in
nit, s/called the way/called all the way/
> + * 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
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH bpf-next] bpf: Remove migrate_disable in kprobe_multi_link_prog_run
2025-08-05 16:04 ` Jiri Olsa
@ 2025-08-05 16:17 ` Tao Chen
0 siblings, 0 replies; 4+ messages in thread
From: Tao Chen @ 2025-08-05 16:17 UTC (permalink / raw)
To: Jiri Olsa
Cc: song, ast, daniel, andrii, martin.lau, eddyz87, yonghong.song,
john.fastabend, kpsingh, sdf, haoluo, mattbobrowski, rostedt,
mhiramat, mathieu.desnoyers, bpf, linux-kernel,
linux-trace-kernel
在 2025/8/6 00:04, Jiri Olsa 写道:
> On Tue, Aug 05, 2025 at 08:23:12PM +0800, Tao Chen wrote:
>> bpf program should run under migration disabled, kprobe_multi_link_prog_run
>> called 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")
>> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
>
> Acked-by: Jiri Olsa <jolsa@kernel.org>
>
> thanks,
> jirka
>
>
>> ---
>> kernel/trace/bpf_trace.c | 9 +++++++--
>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index 3ae52978cae..1993fc62539 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 the way from graph tracer, which disables preemption in
>
> nit, s/called the way/called all the way/
>
will fix it, thanks.
>
>> + * 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
>>
--
Best Regards
Tao Chen
^ permalink raw reply [flat|nested] 4+ messages in thread
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2025-08-05 12:23 [PATCH bpf-next] bpf: Remove migrate_disable in kprobe_multi_link_prog_run Tao Chen
2025-08-05 15:48 ` Yonghong Song
2025-08-05 16:04 ` Jiri Olsa
2025-08-05 16:17 ` Tao Chen
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