Patch "tty: improve tty_insert_flip_char() slow path" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

tty: improve tty_insert_flip_char() slow path

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tty-improve-tty_insert_flip_char-slow-path.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Arnd Bergmann <[email protected]>
Date: Tue, 20 Jun 2017 23:10:42 +0200
Subject: tty: improve tty_insert_flip_char() slow path

From: Arnd Bergmann <[email protected]>

commit 065ea0a7afd64d6cf3464bdd1d8cd227527e2045 upstream.

While working on improving the fast path of tty_insert_flip_char(), I noticed that by calling tty_buffer_request_room(), we needlessly move to the separate flag buffer mode for the tty, even when all characters use TTY_NORMAL as the flag.

This changes the code to call __tty_buffer_request_room() with the correct flag, which will then allocate a regular buffer when it rounds out of space but no special flags have been used. I'm guessing that this is the behavior that Peter Hurley intended when he introduced the compacted flip buffers.

---
 drivers/tty/tty_buffer.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

@@ -375,10 +375,11 @@ int __tty_insert_flip_char(struct tty_po
 	struct tty_buffer *tb = port->buf.tail;
 	int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
 
-	if (!tty_buffer_request_room(port, 1))
+	if (!__tty_buffer_request_room(port, 1, flags))
 		return 0;
 
-	*flag_buf_ptr(tb, tb->used) = flag;
+	if (~tb->flags & TTYB_NORMAL)
+		*flag_buf_ptr(tb, tb->used) = flag;
 	*char_buf_ptr(tb, tb->used++) = ch;
 
 	return 1;

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/tty-fix-__tty_insert_flip_char-regression.patch queue-4.13/tty-improve-tty_insert_flip_char-fast-path.patch queue-4.13/tty-improve-tty_insert_flip_char-slow-path.patch