linux-kernel - Re: [RFC][PATCH v3 1/4] printk: move can_use_console out of console_trylock_for

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Date:	Wed, 10 Feb 2016 17:48:16 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.com>, Tejun Heo <tj@...nel.org>,
	Kyle McMartin <kyle@...nel.org>,
	Dave Jones <davej@...emonkey.org.uk>,
	Calvin Owens <calvinowens@...com>,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCH v3 1/4] printk: move can_use_console out of
 console_trylock_for_printk

On Sat 2016-01-23 17:15:10, Sergey Senozhatsky wrote:
> This patch moves can_use_console() check out of
> console_trylock_for_printk(). Instead it calls it in
> console_unlock(), so now console_lock()/console_unlock() are
> also 'protected' by can_use_console().
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> ---
>  kernel/printk/printk.c | 86 ++++++++++++++++++++++++--------------------------
>  1 file changed, 42 insertions(+), 44 deletions(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 7ebcfea..c39232a 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1519,21 +1492,7 @@ static inline int can_use_console(unsigned int cpu)
>   */
>  static int console_trylock_for_printk(void)
>  {
> -	unsigned int cpu = smp_processor_id();
> -
> -	if (!console_trylock())
> -		return 0;
> -	/*
> -	 * If we can't use the console, we need to release the console
> -	 * semaphore by hand to avoid flushing the buffer. We need to hold the
> -	 * console semaphore in order to do this test safely.
> -	 */
> -	if (!can_use_console(cpu)) {
> -		console_locked = 0;
> -		up_console_sem();
> -		return 0;
> -	}
> -	return 1;
> +	return console_trylock();
>  }

I would personally remove console_trylock_for_printk() already in this
patch. I mean to fold the 3rd patch into this one.

>  int printk_delay_msec __read_mostly;

> @@ -2247,9 +2233,21 @@ void console_unlock(void)
>  	do_cond_resched = console_may_schedule;
>  	console_may_schedule = 0;
>  
> +again:
> +	/*
> +	 * We released the console_sem lock, so we need to recheck if
> +	 * cpu is online and (if not) is there at least one CON_ANYTIME
> +	 * console.
> +	 */
> +	if (!can_use_console()) {
> +		console_locked = 0;
> +		up_console_sem();
> +		return;
> +	}

This is a bug fix and a nice clean up together.

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr