Merge branch 'tty-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty-2.6

* 'tty-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty-2.6:
  n_gsm: Fix length handling
  n_gsm: Copy n2 over when configuring via ioctl interface
  serial: bfin_5xx: grab port lock before making port termios changes
  serial: bfin_5xx: disable CON_PRINTBUFFER for consoles
  serial: bfin_5xx: remove redundant SSYNC to improve TX speed
  serial: bfin_5xx: always include DMA headers
  vcs: make proper usage of the poll flags
  amiserial: Remove unused variable icount
  8250: Fix tcsetattr to avoid ioctl(TIOCMIWAIT) hang
  tty_ldisc: Fix BUG() on hangup
  TTY: restore tty_ldisc_wait_idle
  SERIAL: blacklist si3052 chip
  drivers/serial/bfin_5xx.c: Fix line continuation defects
  tty: prevent DOS in the flush_to_ldisc
  8250: add support for Kouwell KW-L221N-2
  nozomi: Fix warning from the previous TIOCGCOUNT changes
  tty: fix warning in synclink driver
  tty: Fix formatting in tty.h
  tty: the development tree is now done in git

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index cc1e9850d655..d8210ca00720 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -413,7 +413,8 @@ static void flush_to_ldisc(struct work_struct *work)
 	spin_lock_irqsave(&tty->buf.lock, flags);
 
 	if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
-		struct tty_buffer *head;
+		struct tty_buffer *head, *tail = tty->buf.tail;
+		int seen_tail = 0;
 		while ((head = tty->buf.head) != NULL) {
 			int count;
 			char *char_buf;
@@ -423,6 +424,15 @@ static void flush_to_ldisc(struct work_struct *work)
 			if (!count) {
 				if (head->next == NULL)
 					break;
+				/*
+				  There's a possibility tty might get new buffer
+				  added during the unlock window below. We could
+				  end up spinning in here forever hogging the CPU
+				  completely. To avoid this let's have a rest each
+				  time we processed the tail buffer.
+				*/
+				if (tail == head)
+					seen_tail = 1;
 				tty->buf.head = head->next;
 				tty_buffer_free(tty, head);
 				continue;
@@ -432,7 +442,7 @@ static void flush_to_ldisc(struct work_struct *work)
 			   line discipline as we want to empty the queue */
 			if (test_bit(TTY_FLUSHPENDING, &tty->flags))
 				break;
-			if (!tty->receive_room) {
+			if (!tty->receive_room || seen_tail) {
 				schedule_delayed_work(&tty->buf.work, 1);
 				break;
 			}