[PATCH] printk: remove unnecessary kmalloc() from syslog during clear

[Namit Gupta]

When the request is only for clearing logs, there is no need for
allocation/deallocation. Only the indexes need to be reset and returned.

This patch implements this simple case separately. And syslog_print_all()
is always called with a valid buf and could use a more sane indentation.

Link: http://lkml.kernel.org/r/20180620135951epcas5p3bd2a8f25ec689ca333bce861b527dba2~54wyKcT0_3155531555epcas5p3y@xxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: pankaj.m@xxxxxxxxxxx
Cc: a.sahrawat@xxxxxxxxxxx
Signed-off-by: Namit Gupta <gupta.namit@xxxxxxxxxxx>
Signed-off-by: Himanshu Maithani <himanshu.m@xxxxxxxxxxx>
Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
---
 kernel/printk/printk.c | 111 ++++++++++++++++++++++++++-----------------------
 1 file changed, 58 insertions(+), 53 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 247808333ba4..588f23c9c14f 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1352,71 +1352,68 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 {
 	char *text;
 	int len = 0;
+	u64 next_seq;
+	u64 seq;
+	u32 idx;
 
 	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.
+	 */
+	seq = clear_seq;
+	idx = clear_idx;
+	while (seq < log_next_seq) {
+		struct printk_log *msg = log_from_idx(idx);
 
-		/*
-		 * Find first record that fits, including all following records,
-		 * into the user-provided buffer for this dump.
-		 */
-		seq = clear_seq;
-		idx = clear_idx;
-		while (seq < log_next_seq) {
-			struct printk_log *msg = log_from_idx(idx);
-
-			len += msg_print_text(msg, true, NULL, 0);
-			idx = log_next(idx);
-			seq++;
-		}
+		len += msg_print_text(msg, true, NULL, 0);
+		idx = log_next(idx);
+		seq++;
+	}
 
-		/* move first record forward until length fits into the buffer */
-		seq = clear_seq;
-		idx = clear_idx;
-		while (len > size && seq < log_next_seq) {
-			struct printk_log *msg = log_from_idx(idx);
+	/* move first record forward until length fits into the buffer */
+	seq = clear_seq;
+	idx = clear_idx;
+	while (len > size && seq < log_next_seq) {
+		struct printk_log *msg = log_from_idx(idx);
 
-			len -= msg_print_text(msg, true, NULL, 0);
-			idx = log_next(idx);
-			seq++;
-		}
+		len -= msg_print_text(msg, true, NULL, 0);
+		idx = log_next(idx);
+		seq++;
+	}
 
-		/* last message fitting into this dump */
-		next_seq = log_next_seq;
+	/* last message fitting into this dump */
+	next_seq = log_next_seq;
 
-		len = 0;
-		while (len >= 0 && seq < next_seq) {
-			struct printk_log *msg = log_from_idx(idx);
-			int textlen;
+	len = 0;
+	while (len >= 0 && seq < next_seq) {
+		struct printk_log *msg = log_from_idx(idx);
+		int textlen;
 
-			textlen = msg_print_text(msg, true, text,
-						 LOG_LINE_MAX + PREFIX_MAX);
-			if (textlen < 0) {
-				len = textlen;
-				break;
-			}
-			idx = log_next(idx);
-			seq++;
+		textlen = msg_print_text(msg, true, text,
+					 LOG_LINE_MAX + PREFIX_MAX);
+		if (textlen < 0) {
+			len = textlen;
+			break;
+		}
+		idx = log_next(idx);
+		seq++;
 
-			logbuf_unlock_irq();
-			if (copy_to_user(buf + len, text, textlen))
-				len = -EFAULT;
-			else
-				len += textlen;
-			logbuf_lock_irq();
-
-			if (seq < log_first_seq) {
-				/* messages are gone, move to next one */
-				seq = log_first_seq;
-				idx = log_first_idx;
-			}
+		logbuf_unlock_irq();
+		if (copy_to_user(buf + len, text, textlen))
+			len = -EFAULT;
+		else
+			len += textlen;
+		logbuf_lock_irq();
+
+		if (seq < log_first_seq) {
+			/* messages are gone, move to next one */
+			seq = log_first_seq;
+			idx = log_first_idx;
 		}
 	}
 
@@ -1430,6 +1427,14 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	return len;
 }
 
+static void syslog_clear(void)
+{
+	logbuf_lock_irq();
+	clear_seq = log_next_seq;
+	clear_idx = log_next_idx;
+	logbuf_unlock_irq();
+}
+
 int do_syslog(int type, char __user *buf, int len, int source)
 {
 	bool clear = false;
@@ -1474,7 +1479,7 @@ int do_syslog(int type, char __user *buf, int len, int source)
 		break;
 	/* Clear ring buffer */
 	case SYSLOG_ACTION_CLEAR:
-		syslog_print_all(NULL, 0, true);
+		syslog_clear();
 		break;
 	/* Disable logging to console */
 	case SYSLOG_ACTION_CONSOLE_OFF:
-- 
2.13.7