Re: [PATCH] printk: defer_console_output: do not assume interrupts disabled

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2022-02-03 12:35:15 [+0106], John Ogness wrote:
> With commit 458df9fd4815 ("printk: remove separate printk_sched
> buffers and use printk buf instead") defer_console_output() was
> changed to no longer disable interrupts. However, it used the
> function __this_cpu_or(), which assumes interrupts disabled. That
> also should have been changed to this_cpu_or().
> 
> Although defer_console_output() is mostly used when interrupts are
> disabled, this is not always the case. One example is
> get_random_bytes(), which is often called with interrupts enabled.

It is okay for __this_cpu_or() to be invoked with disabled preemption if
that is true for all callers. Disabled interrupts or not is not
important as long as there are no callers in_irq(). I believe that there
are callers in_irq() and therefore this_cpu_or() is correct.

>   get_random_bytes()
>     warn_unseeded_randomness()
>       printk_deferred()
> 
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Sebastian