From: Florian Lehner <dev@der-flo.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: acme@kernel.org, andrii@kernel.org, ast@kernel.org,
bpf@vger.kernel.org, daniel@iogearbox.net,
john.fastabend@gmail.com, kafai@fb.com,
linux-kernel@vger.kernel.org, mingo@redhat.com,
netdev@vger.kernel.org
Subject: Re: [FIX bpf,perf] bpf,perf: return EOPNOTSUPP for bpf handler on PERF_COUNT_SW_DUMMY
Date: Tue, 17 Nov 2020 16:39:02 +0100 [thread overview]
Message-ID: <20201117153902.GA6933@der-flo.net> (raw)
In-Reply-To: <20201117075334.GJ3121392@hirez.programming.kicks-ass.net>
On Tue, Nov 17, 2020 at 08:53:34AM +0100, Peter Zijlstra wrote:
> On Mon, Nov 16, 2020 at 01:02:09PM -0800, Martin KaFai Lau wrote:
> > On Mon, Nov 16, 2020 at 07:37:52PM +0100, Florian Lehner wrote:
> > > bpf handlers for perf events other than tracepoints, kprobes or uprobes
> > > are attached to the overflow_handler of the perf event.
> > >
> > > Perf events of type software/dummy are placeholder events. So when
> > > attaching a bpf handle to an overflow_handler of such an event, the bpf
> > > handler will not be triggered.
> > >
> > > This fix returns the error EOPNOTSUPP to indicate that attaching a bpf
> > > handler to a perf event of type software/dummy is not supported.
> > >
> > > Signed-off-by: Florian Lehner <dev@der-flo.net>
> > It is missing a Fixes tag.
>
> I don't think it actually fixes anything. worse it could break things.
>
> Atatching a bpf filter to a dummy event is pointless, but harmless. We
> allow it now, disallowing it will break whatever programs out there are
> doing harmless silly things.
>
> I really don't see the point of this patch. It grows the kernel code for
> absolutely no distinguishable benefit.
I agree, this fix does not implement the functionality of attaching a
bpf handler to a perf event of type software/dummy. Instead it returns
an error code and let the user know that this kind of action is not
supported (yet).
As a user I would prefer to get an error for something that is pointless
than needing to debug why an attached bpf handler is never execute.
Do you think it would be better to improve documentation to point this
out? And if so, which documentation would be best to update?
prev parent reply other threads:[~2020-11-17 15:41 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-16 18:37 [FIX bpf,perf] bpf,perf: return EOPNOTSUPP for bpf handler on PERF_COUNT_SW_DUMMY Florian Lehner
2020-11-16 21:02 ` Martin KaFai Lau
2020-11-17 7:53 ` Peter Zijlstra
2020-11-17 15:39 ` Florian Lehner [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201117153902.GA6933@der-flo.net \
--to=dev@der-flo.net \
--cc=acme@kernel.org \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=john.fastabend@gmail.com \
--cc=kafai@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).