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

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Date:   Wed, 20 Sep 2023 15:08:50 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printk/nbcon: Add assert that CPU migration is disabled
 when calling nbcon_context_try_acquire()

On Wed 2023-09-20 15:06:08, John Ogness wrote:
> 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?

Ah, I have missed it. Please, forgot this patch.

Best Regards,
Petr