Re: [PATCH 1/2] bug: Provide WARN_ON.*DEFERRED() macros for console deferred output

[Andrew Morton]

On Tue, 23 Jun 2026 16:26:49 +0200 Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:

> Provide a deferred version of the WARN_ON() macro. It will delay
> flushing the console until a later context. It is needed in a context
> where the caller holds locks which can lead to a deadlock content is
> flushed to the console driver.
> An example would from a warning from within the scheduler resulting in a
> wake-up of a task.
> 
> Deferring the output works by using printk_deferred_enter/ exit() around
> the printing output. This must be used in a context where the task can't
> migrate to another CPU. This should be the case usually, since the
> scheduler would acquire the rq lock whith disabled interrupts, but to be
> safe preemption is disabled to guarantee this.
> 
> In order not to bloat the code on architectures which provide an
> optimized __WARN_FLAGS() define BUGFLAG_DEFERRED which is handled by
> __report_bug() and does not increase the code size.
> 
> Provide the DEFERRED macros based on __WARN_FLAGS and __WARN_FLAGS
> macros. Extend __report_bug() to handle the deferred case.
> 
> ...
>
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -229,7 +230,10 @@ static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long buga
>  		 */
>  		bug->flags |= BUGFLAG_DONE;
>  	}
> -
> +	if (deferred) {
> +		preempt_disable_notrace();
> +		printk_deferred_enter();
> +	}

For some reason the comment over printk_deferred_enter() says
"Interrupts must be disabled for the deferred duration".  Is that the
case for all the printk_deferred_enter() calls which this patch adds?