tty: cumulate and document tty_struct::flow* members

Group the flow flags under a single struct called flow. The new struct
contains 'stopped' and 'tco_stopped' bools which used to be bits in a
bitfield. The struct also contains the lock protecting them to
potentially share the same cache line.

Note that commit c545b66c6922b (tty: Serialize tcflow() with other tty
flow control changes) added a padding to the original bitfield. It was
for the bitfield to occupy a whole 64b word to avoid interferring stores
on Alpha (cannot we evaporate this arch with weird implications to C
code yet?). But it doesn't work as expected as the padding
(tty_struct::unused) is aligned to a 8B boundary too and occupies some
bytes from the next word.

So make it reliable by:
1) setting __aligned of the struct -- that aligns the start, and
2) making 'unsigned long unused[0]' as the last member of the struct --
   pads the end.

This is also the perfect time to start the documentation of tty_struct
where all this lives. So we start by documenting what these bools
actually serve for. And why we do all the alignment dances. Only the few
up-to-date information from the Theodore's comment made it into this new
Kerneldoc comment.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>
Link: https://lore.kernel.org/r/20210505091928.22010-13-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

13 files changed, 47 insertions, 47 deletions

diff --git a/drivers/tty/amiserial.c b/drivers/tty/amiserial.c
index ca48ce5a0862..a4b8876091d2 100644
--- a/drivers/tty/amiserial.c
+++ b/drivers/tty/amiserial.c
@@ -148,7 +148,7 @@ static __inline__ void rtsdtr_ctrl(int bits)
  * ------------------------------------------------------------
  * rs_stop() and rs_start()
  *
- * This routines are called before setting or resetting tty->stopped.
+ * This routines are called before setting or resetting tty->flow.stopped.
  * They enable or disable transmitter interrupts, as necessary.
  * ------------------------------------------------------------
  */
@@ -309,7 +309,7 @@ static void transmit_chars(struct serial_state *info)
 		return;
 	}
 	if (info->xmit.head == info->xmit.tail
-	    || info->tport.tty->stopped
+	    || info->tport.tty->flow.stopped
 	    || info->tport.tty->hw_stopped) {
 		info->IER &= ~UART_IER_THRI;
 	        custom.intena = IF_TBE;
@@ -768,7 +768,7 @@ static void rs_flush_chars(struct tty_struct *tty)
 	unsigned long flags;
 
 	if (info->xmit.head == info->xmit.tail
-	    || tty->stopped
+	    || tty->flow.stopped
 	    || tty->hw_stopped
 	    || !info->xmit.buf)
 		return;
@@ -812,7 +812,7 @@ static int rs_write(struct tty_struct * tty, const unsigned char *buf, int count
 	local_irq_restore(flags);
 
 	if (info->xmit.head != info->xmit.tail
-	    && !tty->stopped
+	    && !tty->flow.stopped
 	    && !tty->hw_stopped
 	    && !(info->IER & UART_IER_THRI)) {
 		info->IER |= UART_IER_THRI;
diff --git a/drivers/tty/moxa.c b/drivers/tty/moxa.c
index 4d4f15b5cd29..847ad3dac107 100644
--- a/drivers/tty/moxa.c
+++ b/drivers/tty/moxa.c
@@ -1221,7 +1221,7 @@ static int moxa_write_room(struct tty_struct *tty)
 {
 	struct moxa_port *ch;
 
-	if (tty->stopped)
+	if (tty->flow.stopped)
 		return 0;
 	ch = tty->driver_data;
 	if (ch == NULL)
@@ -1374,7 +1374,7 @@ static int moxa_poll_port(struct moxa_port *p, unsigned int handle,
 			clear_bit(EMPTYWAIT, &p->statusflags);
 			tty_wakeup(tty);
 		}
-		if (test_bit(LOWWAIT, &p->statusflags) && !tty->stopped &&
+		if (test_bit(LOWWAIT, &p->statusflags) && !tty->flow.stopped &&
 				MoxaPortTxQueue(p) <= WAKEUP_CHARS) {
 			clear_bit(LOWWAIT, &p->statusflags);
 			tty_wakeup(tty);
diff --git a/drivers/tty/mxser.c b/drivers/tty/mxser.c
index 16a852ecbe8a..85271e109014 100644
--- a/drivers/tty/mxser.c
+++ b/drivers/tty/mxser.c
@@ -1118,7 +1118,7 @@ static int mxser_write(struct tty_struct *tty, const unsigned char *buf, int cou
 		total += c;
 	}
 
-	if (info->xmit_cnt && !tty->stopped) {
+	if (info->xmit_cnt && !tty->flow.stopped) {
 		if (!tty->hw_stopped ||
 				(info->type == PORT_16550A) ||
 				(info->board->chip_flag)) {
@@ -1149,7 +1149,7 @@ static int mxser_put_char(struct tty_struct *tty, unsigned char ch)
 	info->xmit_head &= SERIAL_XMIT_SIZE - 1;
 	info->xmit_cnt++;
 	spin_unlock_irqrestore(&info->slock, flags);
-	if (!tty->stopped) {
+	if (!tty->flow.stopped) {
 		if (!tty->hw_stopped ||
 				(info->type == PORT_16550A) ||
 				info->board->chip_flag) {
@@ -1169,7 +1169,7 @@ static void mxser_flush_chars(struct tty_struct *tty)
 	struct mxser_port *info = tty->driver_data;
 	unsigned long flags;
 
-	if (info->xmit_cnt <= 0 || tty->stopped || !info->port.xmit_buf ||
+	if (info->xmit_cnt <= 0 || tty->flow.stopped || !info->port.xmit_buf ||
 			(tty->hw_stopped && info->type != PORT_16550A &&
 			 !info->board->chip_flag))
 		return;
@@ -1917,7 +1917,7 @@ static void mxser_unthrottle(struct tty_struct *tty)
 /*
  * mxser_stop() and mxser_start()
  *
- * This routines are called before setting or resetting tty->stopped.
+ * This routines are called before setting or resetting tty->flow.stopped.
  * They enable or disable transmitter interrupts, as necessary.
  */
 static void mxser_stop(struct tty_struct *tty)
@@ -1963,7 +1963,7 @@ static void mxser_set_termios(struct tty_struct *tty, struct ktermios *old_termi
 
 	/* Handle sw stopped */
 	if ((old_termios->c_iflag & IXON) && !I_IXON(tty)) {
-		tty->stopped = 0;
+		tty->flow.stopped = 0;
 
 		if (info->board->chip_flag) {
 			spin_lock_irqsave(&info->slock, flags);
@@ -2175,7 +2175,7 @@ static void mxser_transmit_chars(struct tty_struct *tty, struct mxser_port *port
 	if (port->port.xmit_buf == NULL)
 		return;
 
-	if (port->xmit_cnt <= 0 || tty->stopped ||
+	if (port->xmit_cnt <= 0 || tty->flow.stopped ||
 			(tty->hw_stopped &&
 			(port->type != PORT_16550A) &&
 			(!port->board->chip_flag))) {
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index c32318da5190..3566bb577eb0 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1289,7 +1289,7 @@ static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
 		}
 	}
 
-	if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
+	if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
 		start_tty(tty);
 		process_echoes(tty);
 	}
@@ -1398,7 +1398,7 @@ static void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 
-	if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
+	if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
 		start_tty(tty);
 		process_echoes(tty);
 	}
@@ -1427,7 +1427,7 @@ static void n_tty_receive_char_closing(struct tty_struct *tty, unsigned char c)
 		if (c == STOP_CHAR(tty))
 			stop_tty(tty);
 		else if (c == START_CHAR(tty) ||
-			 (tty->stopped && !tty->flow_stopped && I_IXANY(tty) &&
+			 (tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
 			  c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
 			  c != SUSP_CHAR(tty))) {
 			start_tty(tty);
@@ -1797,7 +1797,7 @@ static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
 	 * Fix tty hang when I_IXON(tty) is cleared, but the tty
 	 * been stopped by STOP_CHAR(tty) before it.
 	 */
-	if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow_stopped) {
+	if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow.tco_stopped) {
 		start_tty(tty);
 		process_echoes(tty);
 	}
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 9b5d4ae5d8f2..017f28150a32 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -113,7 +113,7 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
 	struct tty_struct *to = tty->link;
 	unsigned long flags;
 
-	if (tty->stopped)
+	if (tty->flow.stopped)
 		return 0;
 
 	if (c > 0) {
@@ -138,7 +138,7 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
 
 static int pty_write_room(struct tty_struct *tty)
 {
-	if (tty->stopped)
+	if (tty->flow.stopped)
 		return 0;
 	return tty_buffer_space_avail(tty->link->port);
 }
diff --git a/drivers/tty/serial/arc_uart.c b/drivers/tty/serial/arc_uart.c
index 1a9444b6b57e..596217d10d5c 100644
--- a/drivers/tty/serial/arc_uart.c
+++ b/drivers/tty/serial/arc_uart.c
@@ -149,7 +149,7 @@ static unsigned int arc_serial_tx_empty(struct uart_port *port)
 /*
  * Driver internal routine, used by both tty(serial core) as well as tx-isr
  *  -Called under spinlock in either cases
- *  -also tty->stopped has already been checked
+ *  -also tty->flow.stopped has already been checked
  *     = by uart_start( ) before calling us
  *     = tx_ist checks that too before calling
  */
diff --git a/drivers/tty/serial/dz.c b/drivers/tty/serial/dz.c
index 4552742c3859..6d91e9b6284d 100644
--- a/drivers/tty/serial/dz.c
+++ b/drivers/tty/serial/dz.c
@@ -115,7 +115,7 @@ static void dz_out(struct dz_port *dport, unsigned offset, u16 value)
  * rs_stop () and rs_start ()
  *
  * These routines are called before setting or resetting
- * tty->stopped. They enable or disable transmitter interrupts,
+ * tty->flow.stopped. They enable or disable transmitter interrupts,
  * as necessary.
  * ------------------------------------------------------------
  */
diff --git a/drivers/tty/synclink_gt.c b/drivers/tty/synclink_gt.c
index 5523cf7bd1c2..1555dccc28af 100644
--- a/drivers/tty/synclink_gt.c
+++ b/drivers/tty/synclink_gt.c
@@ -768,7 +768,7 @@ static int write(struct tty_struct *tty,
 	if (!info->tx_buf || (count > info->max_frame_size))
 		return -EIO;
 
-	if (!count || tty->stopped || tty->hw_stopped)
+	if (!count || tty->flow.stopped || tty->hw_stopped)
 		return 0;
 
 	spin_lock_irqsave(&info->lock, flags);
@@ -889,7 +889,7 @@ static void flush_chars(struct tty_struct *tty)
 		return;
 	DBGINFO(("%s flush_chars entry tx_count=%d\n", info->device_name, info->tx_count));
 
-	if (info->tx_count <= 0 || tty->stopped ||
+	if (info->tx_count <= 0 || tty->flow.stopped ||
 	    tty->hw_stopped || !info->tx_buf)
 		return;
 
@@ -2241,7 +2241,7 @@ static void isr_txeom(struct slgt_info *info, unsigned short status)
 		else
 #endif
 		{
-			if (info->port.tty && (info->port.tty->stopped || info->port.tty->hw_stopped)) {
+			if (info->port.tty && (info->port.tty->flow.stopped || info->port.tty->hw_stopped)) {
 				tx_stop(info);
 				return;
 			}
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 5b5e99604989..9734be2eb00e 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -778,14 +778,14 @@ EXPORT_SYMBOL(tty_hung_up_p);
  *	but not always.
  *
  *	Locking:
- *		flow_lock
+ *		flow.lock
  */
 
 void __stop_tty(struct tty_struct *tty)
 {
-	if (tty->stopped)
+	if (tty->flow.stopped)
 		return;
-	tty->stopped = 1;
+	tty->flow.stopped = true;
 	if (tty->ops->stop)
 		tty->ops->stop(tty);
 }
@@ -794,9 +794,9 @@ void stop_tty(struct tty_struct *tty)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&tty->flow_lock, flags);
+	spin_lock_irqsave(&tty->flow.lock, flags);
 	__stop_tty(tty);
-	spin_unlock_irqrestore(&tty->flow_lock, flags);
+	spin_unlock_irqrestore(&tty->flow.lock, flags);
 }
 EXPORT_SYMBOL(stop_tty);
 
@@ -809,14 +809,14 @@ EXPORT_SYMBOL(stop_tty);
  *	start method is invoked and the line discipline woken.
  *
  *	Locking:
- *		flow_lock
+ *		flow.lock
  */
 
 void __start_tty(struct tty_struct *tty)
 {
-	if (!tty->stopped || tty->flow_stopped)
+	if (!tty->flow.stopped || tty->flow.tco_stopped)
 		return;
-	tty->stopped = 0;
+	tty->flow.stopped = false;
 	if (tty->ops->start)
 		tty->ops->start(tty);
 	tty_wakeup(tty);
@@ -826,9 +826,9 @@ void start_tty(struct tty_struct *tty)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&tty->flow_lock, flags);
+	spin_lock_irqsave(&tty->flow.lock, flags);
 	__start_tty(tty);
-	spin_unlock_irqrestore(&tty->flow_lock, flags);
+	spin_unlock_irqrestore(&tty->flow.lock, flags);
 }
 EXPORT_SYMBOL(start_tty);
 
@@ -1172,7 +1172,7 @@ ssize_t redirected_tty_write(struct kiocb *iocb, struct iov_iter *iter)
 
 int tty_send_xchar(struct tty_struct *tty, char ch)
 {
-	int	was_stopped = tty->stopped;
+	bool was_stopped = tty->flow.stopped;
 
 	if (tty->ops->send_xchar) {
 		down_read(&tty->termios_rwsem);
@@ -3141,7 +3141,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
 	INIT_WORK(&tty->hangup_work, do_tty_hangup);
 	mutex_init(&tty->atomic_write_lock);
 	spin_lock_init(&tty->ctrl_lock);
-	spin_lock_init(&tty->flow_lock);
+	spin_lock_init(&tty->flow.lock);
 	spin_lock_init(&tty->files_lock);
 	INIT_LIST_HEAD(&tty->tty_files);
 	INIT_WORK(&tty->SAK_work, do_SAK_work);
diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index 41f7449d0464..07c88ccfb17a 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -846,20 +846,20 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
 			return retval;
 		switch (arg) {
 		case TCOOFF:
-			spin_lock_irq(&tty->flow_lock);
-			if (!tty->flow_stopped) {
-				tty->flow_stopped = 1;
+			spin_lock_irq(&tty->flow.lock);
+			if (!tty->flow.tco_stopped) {
+				tty->flow.tco_stopped = true;
 				__stop_tty(tty);
 			}
-			spin_unlock_irq(&tty->flow_lock);
+			spin_unlock_irq(&tty->flow.lock);
 			break;
 		case TCOON:
-			spin_lock_irq(&tty->flow_lock);
-			if (tty->flow_stopped) {
-				tty->flow_stopped = 0;
+			spin_lock_irq(&tty->flow.lock);
+			if (tty->flow.tco_stopped) {
+				tty->flow.tco_stopped = false;
 				__start_tty(tty);
 			}
-			spin_unlock_irq(&tty->flow_lock);
+			spin_unlock_irq(&tty->flow.lock);
 			break;
 		case TCIOFF:
 			if (STOP_CHAR(tty) != __DISABLED_CHAR)
diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 303c198fbf5c..0eb523207828 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -587,7 +587,7 @@ int tty_port_close_start(struct tty_port *port,
 
 	if (tty_port_initialized(port)) {
 		/* Don't block on a stalled port, just pull the chain */
-		if (tty->flow_stopped)
+		if (tty->flow.tco_stopped)
 			tty_driver_flush_buffer(tty);
 		if (port->closing_wait != ASYNC_CLOSING_WAIT_NONE)
 			tty_wait_until_sent(tty, port->closing_wait);
diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 5d2309742718..4b0d69042ceb 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -515,7 +515,7 @@ static void fn_hold(struct vc_data *vc)
 	 * these routines are also activated by ^S/^Q.
 	 * (And SCROLLOCK can also be set by the ioctl KDSKBLED.)
 	 */
-	if (tty->stopped)
+	if (tty->flow.stopped)
 		start_tty(tty);
 	else
 		stop_tty(tty);
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index e5040bdadcd6..38c677fb6505 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2888,7 +2888,7 @@ static int do_con_write(struct tty_struct *tty, const unsigned char *buf, int co
 
 	param.vc = vc;
 
-	while (!tty->stopped && count) {
+	while (!tty->flow.stopped && count) {
 		int orig = *buf;
 		buf++;
 		n++;
@@ -3265,7 +3265,7 @@ static int con_put_char(struct tty_struct *tty, unsigned char ch)
 
 static int con_write_room(struct tty_struct *tty)
 {
-	if (tty->stopped)
+	if (tty->flow.stopped)
 		return 0;
 	return 32768;		/* No limit, really; we're not buffering */
 }