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

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Date:   Sun, 21 Mar 2021 14:34:12 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH next v1 1/3] printk: track/limit recursion

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