tty: Fix spurious poll() wakeups (57087d51) · Commits · 戴 / test

When the N_TTY line discipline receives data and wakes readers to process the input, polling writers are also mistakenly woken. This is because, although readers and writers are differentiated by different wait queues (tty->read_wait & tty->write_wait), both wait queues are polled together. Thus, reader wakeups without poll flags still cause poll(POLLOUT) to wakeup. For received data, wakeup readers with POLLIN. Preserve the unspecific wakeup in n_tty_packet_mode_flush(), as this action should flag both POLLIN and POLLOUT. Fixes epoll_wait() for edge-triggered EPOLLOUT. Signed-off-by:

Peter Hurley <peter@hurleysoftware.com> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_tty.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -1166,7 +1166,7 @@ static void n_tty_receive_break(struct tty_struct *tty)
		}
		put_tty_queue('\0', ldata);
		if (waitqueue_active(&tty->read_wait))
		wake_up_interruptible(&tty->read_wait);
		wake_up_interruptible_poll(&tty->read_wait, POLLIN);
		}

		/**
		@@ -1226,7 +1226,7 @@ static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c)
		} else
		put_tty_queue(c, ldata);
		if (waitqueue_active(&tty->read_wait))
		wake_up_interruptible(&tty->read_wait);
		wake_up_interruptible_poll(&tty->read_wait, POLLIN);
		}

		static void
		@@ -1378,7 +1378,7 @@ handle_newline:
		ldata->canon_head = ldata->read_head;
		kill_fasync(&tty->fasync, SIGIO, POLL_IN);
		if (waitqueue_active(&tty->read_wait))
		wake_up_interruptible(&tty->read_wait);
		wake_up_interruptible_poll(&tty->read_wait, POLLIN);
		return 0;
		}
		}
		@@ -1679,7 +1679,7 @@ static void __receive_buf(struct tty_struct tty, const unsigned char cp,
		L_EXTPROC(tty)) {
		kill_fasync(&tty->fasync, SIGIO, POLL_IN);
		if (waitqueue_active(&tty->read_wait))
		wake_up_interruptible(&tty->read_wait);
		wake_up_interruptible_poll(&tty->read_wait, POLLIN);
		}
		}

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