printk: Remove unnecessary kmalloc() from syslog during clear

When the request is only for clearing logs, there is no need for
allocation/deallocation. Only the indexes need to be reset and returned.
Rest of the patch is mostly made up of changes because of indention.

Link: http://lkml.kernel.org/r/20180620135951epcas5p3bd2a8f25ec689ca333bce861b527dba2~54wyKcT0_3155531555epcas5p3y@epcas5p3.samsung.com
Cc: linux-kernel@vger.kernel.org
Cc: pankaj.m@samsung.com
Cc: a.sahrawat@samsung.com
Signed-off-by: Namit Gupta <gupta.namit@samsung.com>
Signed-off-by: Himanshu Maithani <himanshu.m@samsung.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>

kernel/printk/printk.c

@@ -1352,17 +1352,25 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 {
 	char *text;
 	int len = 0;
+	u64 next_seq;
+	u64 seq;
+	u32 idx;
+
+	if (!buf) {
+		if (clear) {
+			logbuf_lock_irq();
+			clear_seq = log_next_seq;
+			clear_idx = log_next_idx;
+			logbuf_unlock_irq();
+		}
+		return 0;
+	}
 
 	text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
 	if (!text)
 		return -ENOMEM;
 
 	logbuf_lock_irq();
-	if (buf) {
-		u64 next_seq;
-		u64 seq;
-		u32 idx;
-
 	/*
 	 * Find first record that fits, including all following records,
 	 * into the user-provided buffer for this dump.
@@ -1418,7 +1426,6 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 			idx = log_first_idx;
 		}
 	}
-	}
 
 	if (clear) {
 		clear_seq = log_next_seq;