Re: [PATCH v4] lib/vsprintf: defer filling siphash key on RT

From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	John Ogness <john.ogness@linutronix.de>,
	Mike Galbraith <efault@gmx.de>, Petr Mladek <pmladek@suse.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v4] lib/vsprintf: defer filling siphash key on RT
Date: Mon, 1 Aug 2022 15:55:17 +0200	[thread overview]
Message-ID: <CAHmME9qP2ZR6oQY3bf8W42RHW+-DamrzT=Gh1XJ3O7f72NU_bQ@mail.gmail.com> (raw)
In-Reply-To: <YufZVy5adMfl3n9g@linutronix.de>

Hi Sebastian,

On 8/1/22, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> You do remember the warning that poped up in random core with
> CONFIG_PROVE_RAW_LOCK_NESTING enabled? Where I said it does not affect
> !RT it just points out a RT problem in a !RT config?
> If you fix this with one code path for RT and another one for !RT then
> you will have this warning _if_ the caller has a raw_spinlock_t
> acquired.

CONFIG_PROVE_RAW_LOCK_NESTING catches RT issues on non-RT. It doesn't
catch non-RT issues. So lockdep isn't actually warning about something
real as far as non-RT is concerned when CONFIG_PROVE_RAW_LOCK_NESTING
is enabled.

So probably this v4 patch should expand that condition to be:

IS_ENABLED(CONFIG_PROVE_RAW_LOCK_NESTING) || IS_ENABLED(CONFIG_PREEMPT_RT)

That's somewhat distasteful, I realize, but it *does* make the code
actually match reality, which is maybe better.

Jason