[PATCH v2] kexec: fix the unexpected kexec_dprintk() macro

[Dave Young]

On Tue, 9 Apr 2024 at 12:23, Baoquan He <bhe at redhat.com> 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() instead which are expected to work.

Could you also update the kernel/crash_core.c and
kernel/crash_reserve.c to include the filename prefix?
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

Otherwise:
Reviewed-by: Dave Young <dyoung at redhat.com>

>
> Fixes: cbc2fe9d9cb2 ("kexec_file: add kexec_file flag to control debug printing")
> Signed-off-by: Baoquan He <bhe at redhat.com>
> Reported-by: Jiri Slaby <jirislaby at kernel.org>
> Closes: https://lore.kernel.org/all/4c775fca-5def-4a2d-8437-7130b02722a2@kernel.org
> ---
> v1->v2:
> - Change to use pr_info() only when "kexec -s -d" is specified. With
>   this change, those debugging message for "kexec -c -d" of kexec_load
>   will be missed. We'll see if we need add them for kexec_load too, if
>   someone explicitly requests it.
>
>  include/linux/kexec.h | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 060835bb82d5..f31bd304df45 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -461,10 +461,8 @@ static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) {
>
>  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, arg...) \
> +        do { if (kexec_file_dbg_print) pr_info(fmt, ##arg); } while (0)
>
>  #else /* !CONFIG_KEXEC_CORE */
>  struct pt_regs;
> --
> 2.41.0
>
>