[PATCH] new tty buffering locking fix
Change locking in the new tty buffering facility from using tty->read_lock,
which is currently ignored by drivers and thus ineffective. New locking
uses a new tty buffering specific lock enforced centrally in the tty
buffering code.
Two drivers (esp and cyclades) are updated to use the tty buffering
functions instead of accessing tty buffering internals directly. This is
required for the new locking to work.
Minor checks for NULL buffers added to
tty_prepare_flip_string/tty_prepare_flip_string_flags
Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index eb8b5be..076e07c 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -253,6 +253,7 @@
static void tty_buffer_init(struct tty_struct *tty)
{
+ spin_lock_init(&tty->buf.lock);
tty->buf.head = NULL;
tty->buf.tail = NULL;
tty->buf.free = NULL;
@@ -266,6 +267,7 @@
p->used = 0;
p->size = size;
p->next = NULL;
+ p->active = 0;
p->char_buf_ptr = (char *)(p->data);
p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
/* printk("Flip create %p\n", p); */
@@ -312,25 +314,36 @@
int tty_buffer_request_room(struct tty_struct *tty, size_t size)
{
- struct tty_buffer *b = tty->buf.tail, *n;
- int left = 0;
+ struct tty_buffer *b, *n;
+ int left;
+ unsigned long flags;
+
+ spin_lock_irqsave(&tty->buf.lock, flags);
/* OPTIMISATION: We could keep a per tty "zero" sized buffer to
remove this conditional if its worth it. This would be invisible
to the callers */
- if(b != NULL)
+ if ((b = tty->buf.tail) != NULL) {
left = b->size - b->used;
- if(left >= size)
- return size;
- /* This is the slow path - looking for new buffers to use */
- n = tty_buffer_find(tty, size);
- if(n == NULL)
- return left;
- if(b != NULL)
- b->next = n;
- else
- tty->buf.head = n;
- tty->buf.tail = n;
+ b->active = 1;
+ } else
+ left = 0;
+
+ if (left < size) {
+ /* This is the slow path - looking for new buffers to use */
+ if ((n = tty_buffer_find(tty, size)) != NULL) {
+ if (b != NULL) {
+ b->next = n;
+ b->active = 0;
+ } else
+ tty->buf.head = n;
+ tty->buf.tail = n;
+ n->active = 1;
+ } else
+ size = left;
+ }
+
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
return size;
}
@@ -396,10 +409,12 @@
int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars, size_t size)
{
int space = tty_buffer_request_room(tty, size);
- struct tty_buffer *tb = tty->buf.tail;
- *chars = tb->char_buf_ptr + tb->used;
- memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
- tb->used += space;
+ if (likely(space)) {
+ struct tty_buffer *tb = tty->buf.tail;
+ *chars = tb->char_buf_ptr + tb->used;
+ memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
+ tb->used += space;
+ }
return space;
}
@@ -416,10 +431,12 @@
int tty_prepare_flip_string_flags(struct tty_struct *tty, unsigned char **chars, char **flags, size_t size)
{
int space = tty_buffer_request_room(tty, size);
- struct tty_buffer *tb = tty->buf.tail;
- *chars = tb->char_buf_ptr + tb->used;
- *flags = tb->flag_buf_ptr + tb->used;
- tb->used += space;
+ if (likely(space)) {
+ struct tty_buffer *tb = tty->buf.tail;
+ *chars = tb->char_buf_ptr + tb->used;
+ *flags = tb->flag_buf_ptr + tb->used;
+ tb->used += space;
+ }
return space;
}
@@ -2747,20 +2764,20 @@
schedule_delayed_work(&tty->buf.work, 1);
goto out;
}
- spin_lock_irqsave(&tty->read_lock, flags);
- while((tbuf = tty->buf.head) != NULL) {
+ spin_lock_irqsave(&tty->buf.lock, flags);
+ while((tbuf = tty->buf.head) != NULL && !tbuf->active) {
tty->buf.head = tbuf->next;
if (tty->buf.head == NULL)
tty->buf.tail = NULL;
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
/* printk("Process buffer %p for %d\n", tbuf, tbuf->used); */
disc->receive_buf(tty, tbuf->char_buf_ptr,
tbuf->flag_buf_ptr,
tbuf->used);
- spin_lock_irqsave(&tty->read_lock, flags);
+ spin_lock_irqsave(&tty->buf.lock, flags);
tty_buffer_free(tty, tbuf);
}
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
out:
tty_ldisc_deref(disc);
}
@@ -2852,6 +2869,12 @@
void tty_flip_buffer_push(struct tty_struct *tty)
{
+ unsigned long flags;
+ spin_lock_irqsave(&tty->buf.lock, flags);
+ if (tty->buf.tail != NULL)
+ tty->buf.tail->active = 0;
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+
if (tty->low_latency)
flush_to_ldisc((void *) tty);
else