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Date:   Sat, 10 Dec 2022 17:32:27 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Karol Herbst <karolherbst@gmail.com>,
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        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>
Subject: Re: [for-next][PATCH 13/25] x86/mm/kmmio: Use
 rcu_read_lock_sched_notrace()
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On Sat, 10 Dec 2022 13:34:12 -0800
"Paul E. McKenney" <paulmck@kernel.org> wrote:

> > I was going to remove it, but then I realized that it would be a functional
> > change, as from the comment above, it uses "preempt_enable_no_resched(),
> > which there is not a rcu_read_unlock_sched() variant.  
> 
> If this happens often enough, it might be worth adding something like
> rcu_read_unlock_sched_no_resched(), but we clearly are not there yet.
> Especially not with a name like that!  ;-)

Please don't ;-)

This is only to handle the bizarre case that mmio tracing does. Remember,
this tracer is only for those that want to reverse engineer a binary
driver. It's not even SMP safe! When you enable it, it shuts down all but
one CPU. This is actually the reason I worked so hard to keep it working
with lockdep. The shutting down of CPUs has caught so many bugs in other
parts of the kernel! ;-)

Thus, anything that mmio tracer does, is considered niche, and not
something to much care about.

-- Steve