linux-kernel - Re: [PATCH] printk/nbcon: Add assert that CPU migration is disabled when calling nbcon_context_try

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Message-ID: <874jjpt2xz.fsf@jogness.linutronix.de>
Date:   Wed, 20 Sep 2023 15:06:08 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH] printk/nbcon: Add assert that CPU migration is disabled
 when calling nbcon_context_try_acquire()

On 2023-09-20, Petr Mladek <pmladek@...e.com> wrote:
> The nbcon console is locked when the 'prio' and 'cpu' fields in
> console->nbcon_state stay the same. The locking algorithm would
> break when the locked context got migrated to another CPU.
>
> Add assert into nbcon_context_try_acquire(). It would warn when
> the function is called in a context where the CPU migration
> is possible.

static bool nbcon_context_try_acquire(struct nbcon_context *ctxt)
{
        unsigned int cpu = smp_processor_id();

Doesn't smp_processor_id() already provide the necessary checking and
warning?

John