linux-kernel - Re: [PATCHv7 4/8] printk: always use deferred printk when flush printk

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Date:   Wed, 1 Feb 2017 11:06:48 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        Calvin Owens <calvinowens@...com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCHv7 4/8] printk: always use deferred printk when flush
 printk_safe lines

On Tue, 27 Dec 2016 23:16:07 +0900
Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:

> Always use printk_deferred() in printk_safe_flush_line().
> Flushing can be done from NMI or printk_safe contexts (when
> we are in panic), so we can't call console drivers, yet still
> want to store the messages in the logbuf buffer. Therefore we
> use a deferred printk version.
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> Suggested-by: Petr Mladek <pmladek@...e.com>
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> ---
>  kernel/printk/printk_safe.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
> index efc89a4e9df5..054c9128ade0 100644
> --- a/kernel/printk/printk_safe.c
> +++ b/kernel/printk/printk_safe.c
> @@ -113,14 +113,12 @@ static int printk_safe_log_store(struct printk_safe_seq_buf *s,
>  static void printk_safe_flush_line(const char *text, int len)
>  {
>  	/*
> -	 * The buffers are flushed in NMI only on panic.  The messages must
> -	 * go only into the ring buffer at this stage.  Consoles will get
> -	 * explicitly called later when a crashdump is not generated.
> +	 * Avoid any console drivers calls from here, because we may be
> +	 * in NMI or printk_safe context (when in panic). The messages
> +	 * must go only into the ring buffer at this stage.  Consoles will
> +	 * get explicitly called later when a crashdump is not generated.
>  	 */
> -	if (in_nmi())
> -		printk_deferred("%.*s", len, text);
> -	else
> -		printk("%.*s", len, text);
> +	printk_deferred("%.*s", len, text);
>  }

The helper function was there because of the if statement. Just nuke
this function and call printk_deferred() directly. You can move the
comment to the caller.

-- Steve

>  
>  /* printk part of the temporary buffer line by line */