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Commit e8437d7e authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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tty: Make driver-side flip buffers lockless 



Driver-side flip buffer input is already single-threaded; 'publish'
the .next link as the last operation on the tail buffer so the
'consumer' sees the already-completed flip buffer.

The commit buffer index is already 'published' by driver-side functions.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 7bfe0b71

drivers/tty/tty_buffer.c

+4 −27
Original line number Original line Diff line number Diff line
@@ -62,8 +62,6 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size) 
 *

 *

 *	Remove all the buffers pending on a tty whether queued with data

 *	Remove all the buffers pending on a tty whether queued with data

 *	or in the free ring. Must be called when the tty is no longer in use

 *	or in the free ring. Must be called when the tty is no longer in use

 *

 *	Locking: none

 */

 */





void tty_buffer_free_all(struct tty_port *port)

void tty_buffer_free_all(struct tty_port *port)
@@ -216,29 +214,26 @@ void tty_buffer_flush(struct tty_struct *tty) 
 *

 *

 *	Make at least size bytes of linear space available for the tty

 *	Make at least size bytes of linear space available for the tty

 *	buffer. If we fail return the size we managed to find.

 *	buffer. If we fail return the size we managed to find.

 *

 *	Locking: Takes port->buf.lock

 */

 */

int tty_buffer_request_room(struct tty_port *port, size_t size)

int tty_buffer_request_room(struct tty_port *port, size_t size)

{

{

	struct tty_bufhead *buf = &port->buf;

	struct tty_bufhead *buf = &port->buf;

	struct tty_buffer *b, *n;

	struct tty_buffer *b, *n;

	int left;

	int left;

	unsigned long flags;



	spin_lock_irqsave(&buf->lock, flags);

	b = buf->tail;

	b = buf->tail;

	left = b->size - b->used;

	left = b->size - b->used;





	if (left < size) {

	if (left < size) {

		/* This is the slow path - looking for new buffers to use */

		/* This is the slow path - looking for new buffers to use */

		if ((n = tty_buffer_alloc(port, size)) != NULL) {

		if ((n = tty_buffer_alloc(port, size)) != NULL) {

			b->next = n;

			b->commit = b->used;

			buf->tail = n;

			buf->tail = n;

			b->commit = b->used;

			smp_mb();

			b->next = n;

		} else

		} else

			size = left;

			size = left;

	}

	}

	spin_unlock_irqrestore(&buf->lock, flags);

	return size;

	return size;

}

}

EXPORT_SYMBOL_GPL(tty_buffer_request_room);

EXPORT_SYMBOL_GPL(tty_buffer_request_room);
@@ -252,8 +247,6 @@ EXPORT_SYMBOL_GPL(tty_buffer_request_room); 
 *

 *

 *	Queue a series of bytes to the tty buffering. All the characters

 *	Queue a series of bytes to the tty buffering. All the characters

 *	passed are marked with the supplied flag. Returns the number added.

 *	passed are marked with the supplied flag. Returns the number added.

 *

 *	Locking: Called functions may take port->buf.lock

 */

 */





int tty_insert_flip_string_fixed_flag(struct tty_port *port,

int tty_insert_flip_string_fixed_flag(struct tty_port *port,
@@ -288,8 +281,6 @@ EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag); 
 *	Queue a series of bytes to the tty buffering. For each character

 *	Queue a series of bytes to the tty buffering. For each character

 *	the flags array indicates the status of the character. Returns the

 *	the flags array indicates the status of the character. Returns the

 *	number added.

 *	number added.

 *

 *	Locking: Called functions may take port->buf.lock

 */

 */





int tty_insert_flip_string_flags(struct tty_port *port,

int tty_insert_flip_string_flags(struct tty_port *port,
@@ -324,19 +315,14 @@ EXPORT_SYMBOL(tty_insert_flip_string_flags); 
 *	processing by the line discipline.

 *	processing by the line discipline.

 *	Note that this function can only be used when the low_latency flag

 *	Note that this function can only be used when the low_latency flag

 *	is unset. Otherwise the workqueue won't be flushed.

 *	is unset. Otherwise the workqueue won't be flushed.

 *

 *	Locking: Takes port->buf.lock

 */

 */





void tty_schedule_flip(struct tty_port *port)

void tty_schedule_flip(struct tty_port *port)

{

{

	struct tty_bufhead *buf = &port->buf;

	struct tty_bufhead *buf = &port->buf;

	unsigned long flags;

	WARN_ON(port->low_latency);

	WARN_ON(port->low_latency);





	spin_lock_irqsave(&buf->lock, flags);

	buf->tail->commit = buf->tail->used;

	buf->tail->commit = buf->tail->used;

	spin_unlock_irqrestore(&buf->lock, flags);

	schedule_work(&buf->work);

	schedule_work(&buf->work);

}

}

EXPORT_SYMBOL(tty_schedule_flip);

EXPORT_SYMBOL(tty_schedule_flip);
@@ -352,8 +338,6 @@ EXPORT_SYMBOL(tty_schedule_flip); 
 *	accounted for as ready for normal characters. This is used for drivers

 *	accounted for as ready for normal characters. This is used for drivers

 *	that need their own block copy routines into the buffer. There is no

 *	that need their own block copy routines into the buffer. There is no

 *	guarantee the buffer is a DMA target!

 *	guarantee the buffer is a DMA target!

 *

 *	Locking: May call functions taking port->buf.lock

 */

 */





int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,

int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
@@ -382,8 +366,6 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string); 
 *	accounted for as ready for characters. This is used for drivers

 *	accounted for as ready for characters. This is used for drivers

 *	that need their own block copy routines into the buffer. There is no

 *	that need their own block copy routines into the buffer. There is no

 *	guarantee the buffer is a DMA target!

 *	guarantee the buffer is a DMA target!

 *

 *	Locking: May call functions taking port->buf.lock

 */

 */





int tty_prepare_flip_string_flags(struct tty_port *port,

int tty_prepare_flip_string_flags(struct tty_port *port,
@@ -511,18 +493,13 @@ void tty_flush_to_ldisc(struct tty_struct *tty) 
 *

 *

 *	In the event of the queue being busy for flipping the work will be

 *	In the event of the queue being busy for flipping the work will be

 *	held off and retried later.

 *	held off and retried later.

 *

 *	Locking: tty buffer lock. Driver locks in low latency mode.

 */

 */





void tty_flip_buffer_push(struct tty_port *port)

void tty_flip_buffer_push(struct tty_port *port)

{

{

	struct tty_bufhead *buf = &port->buf;

	struct tty_bufhead *buf = &port->buf;

	unsigned long flags;





	spin_lock_irqsave(&buf->lock, flags);

	buf->tail->commit = buf->tail->used;

	buf->tail->commit = buf->tail->used;

	spin_unlock_irqrestore(&buf->lock, flags);





	if (port->low_latency)

	if (port->low_latency)

		flush_to_ldisc(&buf->work);

		flush_to_ldisc(&buf->work);