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tty: Ensure single-threaded flip buffer consumer with mutex

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The buffer work may race with parallel tty_buffer_flush. Use a
mutex to guarantee exclusive modify access to the head flip
buffer.

Remove the unneeded spin lock.

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 09:36:10 -04:00 committed by Greg Kroah-Hartman
parent e8437d7ecb
commit e9975fdec0
3 changed files with 22 additions and 22 deletions
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2
drivers/staging/dgrp/dgrp_tty.c
View File

@ -1120,7 +1120,9 @@ static void dgrp_tty_close(struct tty_struct *tty, struct file *file)
if (!sent_printer_offstr)
dgrp_tty_flush_buffer(tty);
spin_unlock_irqrestore(&nd->nd_lock, lock_flags);
tty_ldisc_flush(tty);
spin_lock_irqsave(&nd->nd_lock, lock_flags);
break;
}

40
drivers/tty/tty_buffer.c
View File

@ -157,8 +157,6 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
* flush all the buffers containing receive data. Caller must
* hold the buffer lock and must have ensured no parallel flush to
* ldisc is running.
*
* Locking: Caller must hold tty->buf.lock
*/
static void __tty_buffer_flush(struct tty_port *port)
@ -182,29 +180,29 @@ static void __tty_buffer_flush(struct tty_port *port)
* being processed by flush_to_ldisc then we defer the processing
* to that function
*
* Locking: none
* Locking: takes flush_mutex to ensure single-threaded flip buffer
* 'consumer'
*/
void tty_buffer_flush(struct tty_struct *tty)
{
struct tty_port *port = tty->port;
struct tty_bufhead *buf = &port->buf;
unsigned long flags;
spin_lock_irqsave(&buf->lock, flags);
mutex_lock(&buf->flush_mutex);
/* If the data is being pushed to the tty layer then we can't
process it here. Instead set a flag and the flush_to_ldisc
path will process the flush request before it exits */
if (test_bit(TTYP_FLUSHING, &port->iflags)) {
set_bit(TTYP_FLUSHPENDING, &port->iflags);
spin_unlock_irqrestore(&buf->lock, flags);
mutex_unlock(&buf->flush_mutex);
wait_event(tty->read_wait,
test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
return;
} else
__tty_buffer_flush(port);
spin_unlock_irqrestore(&buf->lock, flags);
}
__tty_buffer_flush(port);
mutex_unlock(&buf->flush_mutex);
}
/**
@ -408,9 +406,10 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
* This routine is called out of the software interrupt to flush data
* from the buffer chain to the line discipline.
*
* Locking: holds tty->buf.lock to guard buffer list. Drops the lock
* while invoking the line discipline receive_buf method. The
* receive_buf method is single threaded for each tty instance.
* The receive_buf method is single threaded for each tty instance.
*
* Locking: takes flush_mutex to ensure single-threaded flip buffer
* 'consumer'
*/
static void flush_to_ldisc(struct work_struct *work)
@ -418,7 +417,6 @@ static void flush_to_ldisc(struct work_struct *work)
struct tty_port *port = container_of(work, struct tty_port, buf.work);
struct tty_bufhead *buf = &port->buf;
struct tty_struct *tty;
unsigned long flags;
struct tty_ldisc *disc;
tty = port->itty;
@ -429,7 +427,7 @@ static void flush_to_ldisc(struct work_struct *work)
if (disc == NULL)
return;
spin_lock_irqsave(&buf->lock, flags);
mutex_lock(&buf->flush_mutex);
if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
while (1) {
@ -444,11 +442,13 @@ static void flush_to_ldisc(struct work_struct *work)
tty_buffer_free(port, head);
continue;
}
spin_unlock_irqrestore(&buf->lock, flags);
mutex_unlock(&buf->flush_mutex);
count = receive_buf(tty, head, count);
spin_lock_irqsave(&buf->lock, flags);
mutex_lock(&buf->flush_mutex);
/* Ldisc or user is trying to flush the buffers.
We may have a deferred request to flush the
input buffer, if so pull the chain under the lock
@ -464,7 +464,7 @@ static void flush_to_ldisc(struct work_struct *work)
clear_bit(TTYP_FLUSHING, &port->iflags);
}
spin_unlock_irqrestore(&buf->lock, flags);
mutex_unlock(&buf->flush_mutex);
tty_ldisc_deref(disc);
}
@ -514,15 +514,13 @@ EXPORT_SYMBOL(tty_flip_buffer_push);
*
* Set up the initial state of the buffer management for a tty device.
* Must be called before the other tty buffer functions are used.
*
* Locking: none
*/
void tty_buffer_init(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
spin_lock_init(&buf->lock);
mutex_init(&buf->flush_mutex);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;

2
include/linux/tty.h
View File

@ -66,7 +66,7 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs)
struct tty_bufhead {
struct work_struct work;
spinlock_t lock;
struct mutex flush_mutex;
struct tty_buffer sentinel;
struct tty_buffer *head; /* Queue head */
struct tty_buffer *tail; /* Active buffer */