linux-kernel - Re: [PATCH next v3 3/3] printk: remove logbuf

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Date:   Tue, 08 Dec 2020 08:51:32 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH next v3 3/3] printk: remove logbuf_lock protection for ringbuffer

On 2020-12-07, John Ogness <john.ogness@...utronix.de> wrote:
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index e1f068677a74..f3c0fcc3163f 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
[...]
>  int vprintk_store(int facility, int level,
>  		  const struct dev_printk_info *dev_info,
>  		  const char *fmt, va_list args)
>  {
>  	const u32 caller_id = printk_caller_id();
> -	static char textbuf[LOG_LINE_MAX];
>  	struct prb_reserved_entry e;
>  	enum log_flags lflags = 0;
>  	struct printk_record r;
>  	u16 trunc_msg_len = 0;
> -	char *text = textbuf;
> +	char prefix_buf[8];
> +	va_list args2;
>  	u16 text_len;
> +	int ret = 0;
>  	u64 ts_nsec;
>  
>  	/*
> @@ -1884,35 +1951,21 @@ int vprintk_store(int facility, int level,
>  	 */
>  	ts_nsec = local_clock();
>  
> +	va_copy(args2, args);
> +
>  	/*
>  	 * The printf needs to come first; we need the syslog
>  	 * prefix which might be passed-in as a parameter.
>  	 */
> -	text_len = vscnprintf(text, sizeof(textbuf), fmt, args);
> +	text_len = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args) + 1;
> +	if (text_len > CONSOLE_LOG_MAX)
> +		text_len = CONSOLE_LOG_MAX;

LOG_LINE_MAX should be the limit. That was the size of the static
@textbuf.

John Ogness