From: TATSUKAWA KOSUKE (立川 江介) tatsu-ab1@nec.com
stable inclusion from linux-4.19.230 commit 031ec2d7fabb5c01601490671666c55cf92e1b98
--------------------------------
commit c816b2e65b0e86b95011418cad334f0524fc33b8 upstream.
The poll man page says POLLRDNORM is equivalent to POLLIN when used as an event. $ man poll <snip> POLLRDNORM Equivalent to POLLIN.
However, in n_tty driver, POLLRDNORM does not return until timeout even if there is terminal input, whereas POLLIN returns.
The following test program works until kernel-3.17, but the test stops in poll() after commit 57087d515441 ("tty: Fix spurious poll() wakeups").
[Steps to run test program] $ cc -o test-pollrdnorm test-pollrdnorm.c $ ./test-pollrdnorm foo <-- Type in something from the terminal followed by [RET]. The string should be echoed back.
------------------------< test-pollrdnorm.c >------------------------ #include <stdio.h> #include <errno.h> #include <poll.h> #include <unistd.h>
void main(void) { int n; unsigned char buf[8]; struct pollfd fds[1] = {{ 0, POLLRDNORM, 0 }};
n = poll(fds, 1, -1); if (n < 0) perror("poll"); n = read(0, buf, 8); if (n < 0) perror("read"); if (n > 0) write(1, buf, n); } ------------------------------------------------------------------------
The attached patch fixes this problem. Many calls to wake_up_interruptible_poll() in the kernel source code already specify "POLLIN | POLLRDNORM".
Fixes: 57087d515441 ("tty: Fix spurious poll() wakeups") Cc: stable@vger.kernel.org Signed-off-by: Kosuke Tatsukawa tatsu-ab1@nec.com Link: https://lore.kernel.org/r/TYCPR01MB81901C0F932203D30E452B3EA5209@TYCPR01MB81... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Yongqiang Liu liuyongqiang13@huawei.com Signed-off-by: Laibin Qiu qiulaibin@huawei.com --- drivers/tty/n_tty.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 9369f5d2fdf5..a8d7ab7ee057 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -1375,7 +1375,7 @@ n_tty_receive_char_special(struct tty_struct *tty, unsigned char c) put_tty_queue(c, ldata); smp_store_release(&ldata->canon_head, ldata->read_head); kill_fasync(&tty->fasync, SIGIO, POLL_IN); - wake_up_interruptible_poll(&tty->read_wait, EPOLLIN); + wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM); return 0; } } @@ -1656,7 +1656,7 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
if (read_cnt(ldata)) { kill_fasync(&tty->fasync, SIGIO, POLL_IN); - wake_up_interruptible_poll(&tty->read_wait, EPOLLIN); + wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM); } }