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Wed, 08 Jan 2025 03:38:50 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 8 Jan 2025 12:38:48 +0100 To: Song Liu Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Masami Hiramatsu Subject: Re: [PATCH bpf-next 1/2] bpf: Return error for missed kprobe multi bpf program execution Message-ID: References: <20250106175048.1443905-1-jolsa@kernel.org> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Jan 06, 2025 at 02:26:22PM -0800, Song Liu wrote: > On Mon, Jan 6, 2025 at 9:50 AM Jiri Olsa wrote: > > > > When kprobe multi bpf program can't be executed due to recursion check, > > we currently return 0 (success) to fprobe layer where it's ignored for > > standard kprobe multi probes. > > > > For kprobe session the success return value will make fprobe layer to > > install return probe and try to execute it as well. > > > > But the return session probe should not get executed, because the entry > > part did not run. FWIW the return probe bpf program most likely won't get > > executed, because its recursion check will likely fail as well, but we > > don't need to run it in the first place.. also we can make this clear > > and obvious. > > > > It also affects missed counts for kprobe session program execution, which > > are now doubled (extra count for not executed return probe). > > > > Signed-off-by: Jiri Olsa > > --- > > kernel/trace/bpf_trace.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > index 48db147c6c7d..1f3d4b72a3f2 100644 > > --- a/kernel/trace/bpf_trace.c > > +++ b/kernel/trace/bpf_trace.c > > @@ -2797,7 +2797,7 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, > > > > if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) { > > bpf_prog_inc_misses_counter(link->link.prog); > > - err = 0; > > + err = 1; > > nit: Shall we return -EBUSY or some other error code? it's processed in __fprobe_handler and it's treated as bool, so technically it does not matter.. but I'd rather keep the 0/1 return values in here, because it's what the session program is forced to return thanks, jirka