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Date: Tue, 23 Jun 2026 08:12:58 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
 sched-ext@lists.linux.dev, netdev@vger.kernel.org, "David S . Miller"
 <davem@davemloft.net>, Andrea Righi <arighi@nvidia.com>, Arnd Bergmann
 <arnd@arndb.de>, Ben Segall <bsegall@google.com>, Breno Leitao
 <leitao@debian.org>, Changwoo Min <changwoo@igalia.com>, David Vernet
 <void@manifault.com>, Dietmar Eggemann <dietmar.eggemann@arm.com>, Eric
 Dumazet <edumazet@google.com>, Ingo Molnar <mingo@redhat.com>, Jakub
 Kicinski <kuba@kernel.org>, John Ogness <john.ogness@linutronix.de>, Juri
 Lelli <juri.lelli@redhat.com>, K Prateek Nayak <kprateek.nayak@amd.com>,
 Paolo Abeni <pabeni@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
 Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky
 <senozhatsky@chromium.org>, Simon Horman <horms@kernel.org>, Steven Rostedt
 <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>, Vincent Guittot
 <vincent.guittot@linaro.org>, Vlad Poenaru <vlad.wing@gmail.com>
Subject: Re: [PATCH 1/2] bug: Provide WARN_ON.*DEFERRED() macros for console
 deferred output
Message-Id: <20260623081258.580e034fdb5b98f4f8dba44a@linux-foundation.org>
In-Reply-To: <20260623142650.265721-2-bigeasy@linutronix.de>
References: <20260623142650.265721-1-bigeasy@linutronix.de>
	<20260623142650.265721-2-bigeasy@linutronix.de>
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On Tue, 23 Jun 2026 16:26:49 +0200 Sebastian Andrzej Siewior <bigeasy@linutronix.de> 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?