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Wed, 01 Apr 2026 04:11:17 -0700 (PDT) Date: Wed, 1 Apr 2026 16:41:06 +0530 From: Varun R Mallya To: Jiri Olsa Cc: andrii@kernel.org, alan.maguire@oracle.com, yonghong.song@linux.dev, song@kernel.org, bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, memxor@gmail.com, eddyz87@gmail.com, martin.lau@linux.dev, menglong8.dong@gmail.com, puranjay@kernel.org, bjorn@kernel.org, leon.hwang@linux.dev, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH bpf-next v2 3/3] libbpf: Auto-upgrade kprobes to multi-kprobes when supported Message-ID: References: <20260330110019.549079-1-varunrmallya@gmail.com> <20260330110019.549079-4-varunrmallya@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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.)