linux-kernel - Re: [PATCH v1 2/8] tracing/ftrace: guard syscall probe with preempt

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Message-ID: <20241004165927.774e7d35@gandalf.local.home>
Date: Fri, 4 Oct 2024 16:59:27 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Masami Hiramatsu
 <mhiramat@...nel.org>, linux-kernel@...r.kernel.org, Peter Zijlstra
 <peterz@...radead.org>, Alexei Starovoitov <ast@...nel.org>, Yonghong Song
 <yhs@...com>, "Paul E . McKenney" <paulmck@...nel.org>, Ingo Molnar
 <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark
 Rutland <mark.rutland@....com>, Alexander Shishkin
 <alexander.shishkin@...ux.intel.com>, Namhyung Kim <namhyung@...nel.org>,
 bpf@...r.kernel.org, Joel Fernandes <joel@...lfernandes.org>,
 linux-trace-kernel@...r.kernel.org, Michael Jeanson <mjeanson@...icios.com>
Subject: Re: [PATCH v1 2/8] tracing/ftrace: guard syscall probe with
 preempt_notrace

On Fri, 4 Oct 2024 13:04:21 -0700
Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:

> > AFAIU eBPF folks are very eager to start making use of this, so we won't
> > have to wait long.  
> 
> I already gave my ack on BPF parts of this patch set, but I'll
> elaborate a bit more here for the record. There seems to be two things
> that's been discussed.
> 
> First, preempt_disable() vs migrate_disable(). We only need the
> latter, but the former just preserves current behavior and I think
> it's fine, we can follow up with BPF-specific bits later to optimize
> and clean this up further. No big deal.
> 
> Second, whether BPF can utilize sleepable (faultable) tracepoints
> right now with these changes. No, we need a bit more work (again, in
> BPF specific parts) to allow faultable tracepoint attachment for BPF
> programs. But it's a bit nuanced piece of code to get everything
> right, and it's best done by someone more familiar with BPF internals.
> So I wouldn't expect Mathieu to do this either.
> 
> So, tl;dr, I think patches are fine as-is (from BPF perspective), and
> we'd like to see them applied and get to bpf-next for further
> development on top of that.

Thanks Andrii for elaborating.

-- Steve