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tty: Make driver-side flip buffers lockless

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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: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2013-06-15 09:36:09 -04:00 committed by Greg Kroah-Hartman
parent 7bfe0b7116
commit e8437d7ecb
1 changed files with 4 additions and 27 deletions
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31
drivers/tty/tty_buffer.c
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@ -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
* 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)
@ -216,29 +214,26 @@ void tty_buffer_flush(struct tty_struct *tty)
*
* Make at least size bytes of linear space available for the tty
* 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)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *b, *n;
int left;
unsigned long flags;
spin_lock_irqsave(&buf->lock, flags);
b = buf->tail;
left = b->size - b->used;
if (left < size) {
/* This is the slow path - looking for new buffers to use */
if ((n = tty_buffer_alloc(port, size)) != NULL) {
b->next = n;
b->commit = b->used;
buf->tail = n;
b->commit = b->used;
smp_mb();
b->next = n;
} else
size = left;
}
spin_unlock_irqrestore(&buf->lock, flags);
return size;
}
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
* 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,
@ -288,8 +281,6 @@ EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
* Queue a series of bytes to the tty buffering. For each character
* the flags array indicates the status of the character. Returns the
* number added.
*
* Locking: Called functions may take port->buf.lock
*/
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.
* Note that this function can only be used when the low_latency flag
* is unset. Otherwise the workqueue won't be flushed.
*
* Locking: Takes port->buf.lock
*/
void tty_schedule_flip(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
unsigned long flags;
WARN_ON(port->low_latency);
spin_lock_irqsave(&buf->lock, flags);
buf->tail->commit = buf->tail->used;
spin_unlock_irqrestore(&buf->lock, flags);
schedule_work(&buf->work);
}
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
* that need their own block copy routines into the buffer. There is no
* 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,
@ -382,8 +366,6 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
* accounted for as ready for characters. This is used for drivers
* that need their own block copy routines into the buffer. There is no
* 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,
@ -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
* held off and retried later.
*
* Locking: tty buffer lock. Driver locks in low latency mode.
*/
void tty_flip_buffer_push(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
unsigned long flags;
spin_lock_irqsave(&buf->lock, flags);
buf->tail->commit = buf->tail->used;
spin_unlock_irqrestore(&buf->lock, flags);
if (port->low_latency)
flush_to_ldisc(&buf->work);