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

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Date: Thu, 14 Mar 2024 18:39:47 +0800
From: Baoquan He <bhe@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: kexec@...ts.infradead.org,
	jirislaby@...nel.org,
	akpm@...ux-foundation.org,
	joe@...ches.com,
	dyoung@...hat.com,
	Baoquan He <bhe@...hat.com>
Subject: [PATCH] kexec: fix the unexpected kexec_dprintk() macro

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.

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;
-- 
2.41.0