Re: [PATCH next v1 1/3] printk: track/limit recursion

From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH next v1 1/3] printk: track/limit recursion
Date: Sun, 21 Mar 2021 14:34:12 +0900	[thread overview]
Message-ID: <YFba1Fje6+TeIiGW@google.com> (raw)
In-Reply-To: <20210316233326.10778-2-john.ogness@linutronix.de>

On (21/03/17 00:33), John Ogness wrote:
[..]
>  static inline void printk_delay(void)
> @@ -2040,11 +2105,13 @@ int vprintk_store(int facility, int level,
>  	struct prb_reserved_entry e;
>  	enum log_flags lflags = 0;
>  	struct printk_record r;
> +	unsigned long irqflags;
>  	u16 trunc_msg_len = 0;
>  	char prefix_buf[8];
>  	u16 reserve_size;
>  	va_list args2;
>  	u16 text_len;
> +	int ret = 0;
>  	u64 ts_nsec;
>  
>  	/*
> @@ -2055,6 +2122,9 @@ int vprintk_store(int facility, int level,
>  	 */
>  	ts_nsec = local_clock();
>  
> +	if (!printk_enter_irqsave(&irqflags))
> +		return 0;

I guess it can be interesting to somehow signal us that we had printk()
recursion overflow, and how many messages we lost.

3 levels of recursion seem like reasonable limit, but I maybe wouldn't
mind one extra level. And maybe we could add some sort of message prefix
for high levels of recursion nesting (levels 3+), so that things should
not be normal will be on the radars and, possibly, will be reported.

	-ss