Patch "tty: improve tty_insert_flip_char() slow path" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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 4.4-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-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 065ea0a7afd64d6cf3464bdd1d8cd227527e2045 Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@arndb.de>
Date: Tue, 20 Jun 2017 23:10:42 +0200
Subject: tty: improve tty_insert_flip_char() slow path

From: Arnd Bergmann <arnd@arndb.de>

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.

Fixes: acc0f67f307f ("tty: Halve flip buffer GFP_ATOMIC memory consumption")
Cc: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -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 arnd@arndb.de are

queue-4.4/qlge-avoid-memcpy-buffer-overflow.patch
queue-4.4/tty-fix-__tty_insert_flip_char-regression.patch
queue-4.4/tty-improve-tty_insert_flip_char-fast-path.patch
queue-4.4/tty-improve-tty_insert_flip_char-slow-path.patch