linux-kernel - Re: [PATCH] kexec: fix the unexpected kexec

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Date: Thu, 14 Mar 2024 12:54:05 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc: kexec@...ts.infradead.org, akpm@...ux-foundation.org, joe@...ches.com,
 dyoung@...hat.com
Subject: Re: [PATCH] kexec: fix the unexpected kexec_dprintk() macro

On 14. 03. 24, 11:39, Baoquan He wrote:
> Jiri reported that the current kexec_dprintk() always prints out
> debugging message whenever kexec/kdmmp loading is triggered. That is
> not wanted. The debugging message is supposed to be printed out when
> 'kexec -s -d' is specified for kexec/kdump loading.
> 
> After investigating, the reason is the current kexec_dprintk() takes
> printk(KERN_INFO) or printk(KERN_DEBUG) depending on whether '-d' is
> specified. However, distros usually have defaulg log level like below:
> 
>   [~]# cat /proc/sys/kernel/printk
>   7	 4	1	7
> 
> So, even though '-d' is not specified, printk(KERN_DEBUG) also always
> prints out. I thought printk(KERN_DEBUG) is equal to pr_debug(), it's
> not.
> 
> Fix it by changing to use pr_info() and pr_debug() instead which are
> expected to work.

Hi,

sow, you'd need both -d, and dyndbg updates. Hence, again my question:
===
Actually what was wrong on the pr_debug()s? Can you simply turn them on 
from the kernel when -d is passed to kexec instead of all this?
===

And yet, it is still missing a prefix :).

> Signed-off-by: Baoquan He <bhe@...hat.com>
> Reported-by: Jiri Slaby <jirislaby@...nel.org>
> Closes: https://lore.kernel.org/all/4c775fca-5def-4a2d-8437-7130b02722a2@kernel.org
> ---
>   include/linux/kexec.h | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 400cb6c02176..09688e681bf7 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -502,10 +502,13 @@ static inline unsigned int crash_get_elfcorehdr_size(void) { return 0; }
>   
>   extern bool kexec_file_dbg_print;
>   
> -#define kexec_dprintk(fmt, ...)					\
> -	printk("%s" fmt,					\
> -	       kexec_file_dbg_print ? KERN_INFO : KERN_DEBUG,	\
> -	       ##__VA_ARGS__)
> +#define kexec_dprintk(fmt, args...)				\
> +	do {							\
> +		if (kexec_file_dbg_print)			\
> +			pr_info(fmt, ##args);			\
> +		else						\
> +			pr_debug(fmt, ##args);			\
> +	} while (0)
>   
>   #else /* !CONFIG_KEXEC_CORE */
>   struct pt_regs;

-- 
js
suse labs