Re: [RFC PATCH bpf-next v2 3/3] libbpf: Auto-upgrade kprobes to multi-kprobes when supported

[Varun R Mallya <varunrmallya@gmail.com>]

On Wed, Apr 01, 2026 at 04:23:15PM +0530, Varun R Mallya wrote:
> I had to add that check because selftests/bpf/prog_tests/attach_probe.c
> was failing. Sleepable kprobes are not supposed to attach successfully,
> but since this was upgraded to multi, it was doing so. So, I had to stop
> all sleepable kprobes from being upgraded to maintain compatibility.
> 
> I'd like to know if kprobe_multi is even allowed to be sleepable. I
> could not really find any selftests or patches for sleepable kprobe_multi
> functionality anywhere, so I just want to check if this is not actually
> intended behaviour and we are missing a check somewhere.
>

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 0b040a417442..af7079aa0f36 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
        if (!is_kprobe_multi(prog))
                return -EINVAL;

+       /* kprobe_multi is not allowed to be sleepable. */
+       if (prog->sleepable)
+               return -EINVAL;
+
        /* Writing to context is not allowed for kprobes. */
        if (prog->aux->kprobe_write_ctx)
                return -EINVAL;

Adding this removes the need for me to add the sleepable check. Should I
send a patch with this or am I making a mistake here ??
Sleepability for kprobe_multi was never checked (If it's meant to not be
sleepable, that is.)