linux-kernel - Re: [PATCH 1/2] locking: Provide a low overhead do_arch_spin

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Date:   Wed, 21 Sep 2022 18:06:40 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] locking: Provide a low overhead do_arch_spin_lock()
 API

On Wed, 21 Sep 2022 09:21:51 -0400
Waiman Long <longman@...hat.com> wrote:

> There are some code paths in the kernel like tracing or rcu where they
> want to use a spinlock without the lock debugging overhead (lockdep,
> etc). Provide a do_arch_spin_lock() API with proper preemption disabling
> and enabling without any debugging or tracing overhead.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>

Please don't do this. arch_spin_lock() is very special, and if tracing did
it wrong, then it needs to be fixed in the tracing code.

Let's not add handlers to make it easier to use arch_spin_lock(). Tracing
is special and arch_spin_lock() helps keep it from tracing itself.

-- Steve