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

[Baoquan He]

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.

Fixes: cbc2fe9d9cb2 ("kexec_file: add kexec_file flag to control debug printing")
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Reported-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
Closes: https://lore.kernel.org/all/4c775fca-5def-4a2d-8437-7130b02722a2@xxxxxxxxxx
---
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