n_tty: Replace canon_data with index comparison
canon_data represented the # of lines which had been copied
to the receive buffer but not yet copied to the user buffer.
The value was tested to determine if input was available in
canonical mode (and also to force input overrun if the
receive buffer was full but a newline had not been received).
However, the actual count was irrelevent; only whether it was
non-zero (meaning 'is there any input to transfer?'). This
shared count is unnecessary and unsafe with a lockless algorithm.
The same check is made by comparing canon_head with read_tail instead.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 0599b58..1098dd7 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -104,7 +104,6 @@
unsigned int echo_pos;
unsigned int echo_cnt;
- int canon_data;
size_t canon_head;
unsigned int canon_column;
@@ -158,7 +157,7 @@
* characters will be beeped.
*/
if (left <= 0)
- left = ldata->icanon && !ldata->canon_data;
+ left = ldata->icanon && ldata->canon_head == ldata->read_tail;
return left;
}
@@ -237,14 +236,14 @@
unsigned long flags;
raw_spin_lock_irqsave(&ldata->read_lock, flags);
- ldata->read_head = ldata->read_tail = 0;
+ ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
mutex_lock(&ldata->echo_lock);
ldata->echo_pos = ldata->echo_cnt = ldata->echo_overrun = 0;
mutex_unlock(&ldata->echo_lock);
- ldata->canon_head = ldata->canon_data = ldata->erasing = 0;
+ ldata->erasing = 0;
bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
}
@@ -1360,7 +1359,6 @@
set_bit(ldata->read_head & (N_TTY_BUF_SIZE - 1), ldata->read_flags);
put_tty_queue_nolock(c, ldata);
ldata->canon_head = ldata->read_head;
- ldata->canon_data++;
raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
kill_fasync(&tty->fasync, SIGIO, POLL_IN);
if (waitqueue_active(&tty->read_wait))
@@ -1562,7 +1560,6 @@
if (canon_change) {
bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
ldata->canon_head = ldata->read_tail;
- ldata->canon_data = 0;
ldata->erasing = 0;
}
@@ -1713,7 +1710,7 @@
tty_flush_to_ldisc(tty);
if (ldata->icanon && !L_EXTPROC(tty)) {
- if (ldata->canon_data)
+ if (ldata->canon_head != ldata->read_tail)
return 1;
} else if (read_cnt(ldata) >= (amt ? amt : 1))
return 1;
@@ -1850,15 +1847,8 @@
raw_spin_lock_irqsave(&ldata->read_lock, flags);
ldata->read_tail += c;
- if (found) {
+ if (found)
__clear_bit(eol, ldata->read_flags);
- /* this test should be redundant:
- * we shouldn't be reading data if
- * canon_data is 0
- */
- if (--ldata->canon_data < 0)
- ldata->canon_data = 0;
- }
raw_spin_unlock_irqrestore(&ldata->read_lock, flags);
if (found)
@@ -2264,7 +2254,7 @@
{
size_t nr, head, tail;
- if (!ldata->canon_data)
+ if (ldata->canon_head == ldata->read_tail)
return 0;
head = ldata->canon_head;
tail = ldata->read_tail;