linux-kernel - Re: linux-next: manual merge of the rcu tree with the ftrace tree

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Message-ID: <2b4fce38-92c7-4c87-8f62-7c1e665f3bf9@paulmck-laptop>
Date: Tue, 18 Nov 2025 07:05:52 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Yonghong Song <yonghong.song@...ux.dev>,
	Steven Rostedt <rostedt@...dmis.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: linux-next: manual merge of the rcu tree with the ftrace tree

On Tue, Nov 18, 2025 at 08:35:08AM +0100, Sebastian Andrzej Siewior wrote:
> On 2025-11-14 10:31:45 [-0800], Yonghong Song wrote:
> > > I believe that migration needs to be disabled at this point, but I am
> > > again adding Yonghong on CC for his perspective.
> > 
> > Yes, migration needs to be disabled for rt kernel in order to let
> > bpf program running properly.
> 
> Why is disabling migration special in regard to RT kernels vs !RT?
> Why do we need to disable migration given that bpf_prog_run_array()
> already does that? Is there a different entry point? 
> My point why is it required to disable migration on trace-point entry
> for BPF given that the BPF-entry already does so.

When I tried doing without that disabling some weeks back, it broke.

Maybe things have changed since, but I must defer to Yonghong &c.

							Thanx, Paul