linux-kernel - Re: [BUG] Threaded printk breaks early debugging

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Date:   Sun, 12 Jun 2022 12:13:36 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>
Cc:     Peter Geis <pgwipeout@...il.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [BUG] Threaded printk breaks early debugging

On (22/06/10 17:11), John Ogness wrote:
> It would be trivial to provide a boot parameter for this behavior, but I
> think we first need to see a real problem and also see if we can fix
> that problem.

John, Petr, a quick question

Should a situation when we have only one online CPU be enough of a reason
to do direct printing? Otherwise we might not have CPUs to wakeup khtread on,
e.g. when CPU that printk is in atomic section for too long.

---

@@ -480,6 +480,9 @@ static inline bool allow_direct_printing(void)
 	if (!printk_kthreads_available)
 		return true;
 
+	if (num_online_cpus() == 1)
+		return true;
+
 	/*
 	 * Prefer direct printing when the system is in a problematic state.
 	 * The context that sets this state will always see the updated value.