From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753509AbdKJROe (ORCPT ); Fri, 10 Nov 2017 12:14:34 -0500 Received: from mail-qt0-f193.google.com ([209.85.216.193]:44937 "EHLO mail-qt0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753432AbdKJROb (ORCPT ); Fri, 10 Nov 2017 12:14:31 -0500 X-Google-Smtp-Source: AGs4zMaWehejr/CPWC/ejredfkNn0Wtp8jxoo1XI6YIb36BnE6HsIoS2ROTi4DKdydWLrRKsHSZADQ== Date: Fri, 10 Nov 2017 12:14:29 -0500 From: Josef Bacik To: Ingo Molnar Cc: Josef Bacik , rostedt@goodmis.org, mingo@redhat.com, davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, ast@kernel.org, kernel-team@fb.com, daniel@iogearbox.net, Josef Bacik Subject: Re: [PATCH 1/2] bpf: add a bpf_override_function helper Message-ID: <20171110171428.hrw5cpxy4sgzf7mn@destiny> References: <1510086523-8859-1-git-send-email-josef@toxicpanda.com> <1510086523-8859-2-git-send-email-josef@toxicpanda.com> <20171110093459.w2pvo3ntkwbmgnha@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171110093459.w2pvo3ntkwbmgnha@gmail.com> User-Agent: NeoMutt/20170714 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 10, 2017 at 10:34:59AM +0100, Ingo Molnar wrote: > > * Josef Bacik wrote: > > > @@ -551,6 +578,10 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func > > return &bpf_get_stackid_proto; > > case BPF_FUNC_perf_event_read_value: > > return &bpf_perf_event_read_value_proto; > > + case BPF_FUNC_override_return: > > + pr_warn_ratelimited("%s[%d] is installing a program with bpf_override_return helper that may cause unexpected behavior!", > > + current->comm, task_pid_nr(current)); > > + return &bpf_override_return_proto; > > So if this new functionality is used we'll always print this into the syslog? > > The warning is also a bit passive aggressive about informing the user: what > unexpected behavior can happen, what is the worst case? > It's modeled after the other warnings bpf will spit out, but with this feature you are skipping a function and instead returning some arbitrary value, so anything could go wrong if you mess something up. For instance I screwed up my initial test case and made every IO submitted return an error instead of just on the one file system I was attempting to test, so all sorts of hilarity ensued. Thanks, Josef