linux-kernel - [PATCH 1/1] remove unnecessary calls of kmalloc and kfree from syslog_print

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Date:   Wed, 20 Jun 2018 16:39:11 +0530
From:   Namit Gupta <gupta.namit@...sung.com>
To:     pmladek@...e.com, sergey.senozhatsky@...il.com, rostedt@...dmis.org
Cc:     linux-kernel@...r.kernel.org, pankaj.m@...sung.com,
        a.sahrawat@...sung.com, himanshu.m@...sung.com,
        Namit Gupta <gupta.namit@...sung.com>
Subject: [PATCH 1/1] remove unnecessary calls of kmalloc and kfree from
 syslog_print_all.

When the request is only for clearing logs, there is no need for buffer allocation.
So, the indexes could be reset and returned. This will save unnecessary kmalloc/kfree 
calls also.


Signed-off-by: Namit Gupta <gupta.namit@...sung.com>
Signed-off-by: Himanshu Maithani <himanshu.m@...sung.com>

---
 kernel/printk/printk.c | 111 ++++++++++++++++++++++++++-----------------------
 1 file changed, 60 insertions(+), 51 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 512f7c2..53952ce 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1348,71 +1348,80 @@ 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.
-		 */
-		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++;
-		}
+	/*
+	 * 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);
 
-		/* 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++;
-		}
+	/* 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);
 
-		/* last message fitting into this dump */
-		next_seq = log_next_seq;
+		len -= msg_print_text(msg, true, NULL, 0);
+		idx = log_next(idx);
+		seq++;
+	}
 
-		len = 0;
-		while (len >= 0 && seq < next_seq) {
-			struct printk_log *msg = log_from_idx(idx);
-			int textlen;
+	/* last message fitting into this dump */
+	next_seq = log_next_seq;
 
-			textlen = msg_print_text(msg, true, text,
-						 LOG_LINE_MAX + PREFIX_MAX);
-			if (textlen < 0) {
-				len = textlen;
-				break;
-			}
-			idx = log_next(idx);
-			seq++;
+	len = 0;
+	while (len >= 0 && seq < next_seq) {
+		struct printk_log *msg = log_from_idx(idx);
+		int textlen;
 
-			logbuf_unlock_irq();
-			if (copy_to_user(buf + len, text, textlen))
-				len = -EFAULT;
-			else
-				len += textlen;
-			logbuf_lock_irq();
+		textlen = msg_print_text(msg, true, text,
+				LOG_LINE_MAX + PREFIX_MAX);
+		if (textlen < 0) {
+			len = textlen;
+			break;
+		}
+		idx = log_next(idx);
+		seq++;
 
-			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;
 		}
 	}
 
-- 
1.9.1