linux-kernel - Re: [PATCH] printk: finalize records with trailing newlines

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Date:   Thu, 26 Nov 2020 20:32:18 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     John Ogness <john.ogness@...utronix.de>,
        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>,
        Atish Patra <atishp@...shpatra.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] printk: finalize records with trailing newlines


On 2020/11/26 19:48, John Ogness wrote:
> Any record with a trailing newline (LOG_NEWLINE flag) cannot
> be continued because the newline has been stripped and will
> not be visible if the message is appended. This was already
> handled correctly when committing in log_output() but was
> not handled correctly when committing in log_store().
>
> Fixes: f5f022e53b87 ("printk: reimplement log_cont using record extension")
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
>   This is an important bugfix for continuous messages and should
>   be part of the 5.10 release.
>
>   If not applied, newlines will vanish when concatenating
>   continuous with trailing newlines.
Thanks for you quick fix.

Reported-and-tested-by:  Kefeng Wang <wangkefeng.wang@...wei.com>

>   kernel/printk/printk.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index fe64a49344bf..bc1e3b5a97bd 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -528,8 +528,8 @@ static int log_store(u32 caller_id, int facility, int level,
>   	if (dev_info)
>   		memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
>   
> -	/* insert message */
> -	if ((flags & LOG_CONT) || !(flags & LOG_NEWLINE))
> +	/* A message without a trailing newline can be continued. */
> +	if (!(flags & LOG_NEWLINE))
>   		prb_commit(&e);
>   	else
>   		prb_final_commit(&e);