Subject: Re: [PATCH 03/16] printk: move LOG_NOCONS skipping into call_console_drivers()

From: Petr Mladek <[email-masked]>
Date: Mon, 20 Apr 2015 14:50:16 +0200

On Thu 2015-04-16 19:03:40, Tejun Heo wrote:
> When a line is printed by multiple printk invocations, each chunk is
> directly sent out to console drivers so that they don't get lost.
> When the line is completed and stored in the log buffer, the line is
> suppressed from going out to consoles as that'd lead to duplicate
> outputs.  This is tracked with LOG_NOCONS flag.
> 
> The suppression is currently implemented in console_unlock() which
> skips invoking call_console_drivers() for LOG_NOCONS messages.  This
> patch moves the filtering into call_console_drivers() in preparation
> of the planned extended console drivers which will deal with the
> duplicate messages themselves.
> 
> While this makes call_console_drivers() iterate over LOG_NOCONS
> messages, this is extremely unlikely to matter especially given that
> continuation lines aren't that common and also simplifies
> console_unlock() a bit.
> 
> Signed-off-by: Tejun Heo <[email-masked]>
> Cc: Kay Sievers <[email-masked]>
> Cc: Petr Mladek <[email-masked]>
> ---
>  kernel/printk/printk.c | 46 ++++++++++++++++++++++++----------------------
>  1 file changed, 24 insertions(+), 22 deletions(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 5ea6709..0175c46 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1417,7 +1417,8 @@ SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
>   * log_buf[start] to log_buf[end - 1].
>   * The console_lock must be held.
>   */
> -static void call_console_drivers(int level, const char *text, size_t len)
> +static void call_console_drivers(int level, bool nocons,
> +				 const char *text, size_t len)
>  {
>  	struct console *con;
>  
> @@ -1438,6 +1439,13 @@ static void call_console_drivers(int level, const char *text, size_t len)
>  		if (!cpu_online(smp_processor_id()) &&
>  		    !(con->flags & CON_ANYTIME))
>  			continue;
> +		/*
> +		 * Skip record we have buffered and already printed
> +		 * directly to the console when we received it.
> +		 */
> +		if (nocons)
> +			continue;
> +
>  		con->write(con, text, len);
>  	}
>  }
> @@ -1919,7 +1927,8 @@ static struct cont {
>  } cont;
>  static struct printk_log *log_from_idx(u32 idx) { return NULL; }
>  static u32 log_next(u32 idx) { return 0; }
> -static void call_console_drivers(int level, const char *text, size_t len) {}
> +static void call_console_drivers(int level, bool nocons,
> +				 const char *text, size_t len) {}
>  static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev,
>  			     bool syslog, char *buf, size_t size) { return 0; }
>  static size_t cont_print_text(char *text, size_t size) { return 0; }
> @@ -2190,7 +2199,7 @@ static void console_cont_flush(char *text, size_t size)
>  	len = cont_print_text(text, size);
>  	raw_spin_unlock(&logbuf_lock);
>  	stop_critical_timings();
> -	call_console_drivers(cont.level, text, len);
> +	call_console_drivers(cont.level, false, text, len);
>  	start_critical_timings();
>  	local_irq_restore(flags);
>  	return;
> @@ -2234,6 +2243,7 @@ again:
>  		struct printk_log *msg;
>  		size_t len;
>  		int level;
> +		bool nocons;
>  
>  		raw_spin_lock_irqsave(&logbuf_lock, flags);
>  		if (seen_seq != log_next_seq) {
> @@ -2252,38 +2262,30 @@ again:
>  		} else {
>  			len = 0;
>  		}
> -skip:
> +
>  		if (console_seq == log_next_seq)
>  			break;
>  
>  		msg = log_from_idx(console_idx);
> -		if (msg->flags & LOG_NOCONS) {
> -			/*
> -			 * Skip record we have buffered and already printed
> -			 * directly to the console when we received it.
> -			 */
> -			console_idx = log_next(console_idx);
> -			console_seq++;
> -			/*
> -			 * We will get here again when we register a new
> -			 * CON_PRINTBUFFER console. Clear the flag so we
> -			 * will properly dump everything later.
> -			 */
> -			msg->flags &= ~LOG_NOCONS;
> -			console_prev = msg->flags;
> -			goto skip;
> -		}
> -
>  		level = msg->level;
> +		nocons = msg->flags & LOG_NOCONS;
>  		len += msg_print_text(msg, console_prev, false,
>  				      text + len, sizeof(text) - len);
>  		console_idx = log_next(console_idx);
>  		console_seq++;
>  		console_prev = msg->flags;
> +
> +		/*
> +		 * The log will be processed again when we register a new
> +		 * CON_PRINTBUFFER console. Clear the flag so we will
> +		 * properly dump everything later.
> +		 */
> +		msg->flags &= ~LOG_NOCONS;

The previous code cleared LOG_NOCONS before saving flags into
console_prev. Well, the change does not have any real effect.
And the new order makes more sense.

This patch looks fine to me.

Reviewed-by: Petr Mladek <[email-masked]>

Best Regards,
Petr

>  		raw_spin_unlock(&logbuf_lock);
>  
>  		stop_critical_timings();	/* don't trace print latency */
> -		call_console_drivers(level, text, len);
> +		call_console_drivers(level, nocons, text, len);
>  		start_critical_timings();
>  		local_irq_restore(flags);
>  	}
> -- 
> 2.1.0
>