linux-kernel - [PATCH] printk: don't unconditionally shortcut print

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Date:   Sat, 24 Nov 2018 19:50:13 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: [PATCH] printk: don't unconditionally shortcut print_time()

Since /sys/module/printk/parameters/time can change from N to Y between
"msg_print_text() called print_prefix() with buf == NULL" and
"msg_print_text() again calls print_prefix() with buf != NULL", it is not
safe for print_time() to unconditionally return 0 if printk_time == false.

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
 kernel/printk/printk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5c2079d..df7ced0 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1230,7 +1230,7 @@ static size_t print_time(u64 ts, char *buf)
 {
 	unsigned long rem_nsec;
 
-	if (!printk_time)
+	if (!printk_time && buf)
 		return 0;
 
 	rem_nsec = do_div(ts, 1000000000);
-- 
1.8.3.1