Commit 06c49f9f authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
Browse files

n_tty: Fix PARMRK over-throttling 



If PARMRK is enabled, the available read buffer space computation is
overly-pessimistic, which results in severely throttled i/o, even
in the absence of parity errors. For example, if the 4k read buffer
contains 1k processed data, the input worker will compute available
space of 333 bytes, despite 3k being available. At 1365 chars of
processed data, 0 space available is computed.

*Divide remaining space* by 3, truncating down (if left == 2, left = 0).

Reported-by: default avatarChristian Riesch <christian.riesch@omicron.at>

Conflicts:
	drivers/tty/n_tty.c

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 70aca71f

drivers/tty/n_tty.c

+4 −8
Original line number Original line Diff line number Diff line
@@ -1669,9 +1669,8 @@ n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp, 




	while (1) {

	while (1) {

		/*

		/*

		 * When PARMRK is set, multiply read_cnt by 3, since each byte

		 * When PARMRK is set, each input char may take up to 3 chars

		 * might take up to three times as many spaces (depending on

		 * in the read buf; reduce the buffer space avail by 3x

		 * its flags, e.g. parity error). [This calculation is wrong.]

		 *

		 *

		 * If we are doing input canonicalization, and there are no

		 * If we are doing input canonicalization, and there are no

		 * pending newlines, let characters through without limit, so

		 * pending newlines, let characters through without limit, so
@@ -1683,13 +1682,10 @@ n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp, 
		 * read_tail (so this producer will not overwrite unread data)

		 * read_tail (so this producer will not overwrite unread data)

		 */

		 */

		size_t tail = smp_load_acquire(&ldata->read_tail);

		size_t tail = smp_load_acquire(&ldata->read_tail);

		size_t head = ldata->read_head;





		room = N_TTY_BUF_SIZE - (ldata->read_head - tail) - 1;

		if (I_PARMRK(tty))

		if (I_PARMRK(tty))

			room = N_TTY_BUF_SIZE - (head - tail) * 3 - 1;

			room /= 3;

		else

			room = N_TTY_BUF_SIZE - (head - tail) - 1;



		if (room <= 0)

		if (room <= 0)

			room = ldata->icanon && ldata->canon_head == tail;

			room = ldata->icanon && ldata->canon_head == tail;