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[PATCH] tty buffering stall fix

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Prevent stalled processing of received data when a driver allocates tty
buffer space but does not immediately follow the allocation with more data
and a call to schedule receive tty processing.  (example: hvc_console) This
bug was introduced by the first locking patch for the new tty buffering.

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>
This commit is contained in:
Paul Fulghum 2006-02-10 01:51:14 -08:00 committed by Linus Torvalds
parent f0188f4748
commit 8977d929e4
4 changed files with 30 additions and 10 deletions
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30
drivers/char/tty_io.c
View file

@ -268,6 +268,8 @@ static struct tty_buffer *tty_buffer_alloc(size_t size)
p->size = size;
p->next = NULL;
p->active = 0;
p->commit = 0;
p->read = 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); */
@ -298,6 +300,8 @@ static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
*tbh = t->next;
t->next = NULL;
t->used = 0;
t->commit = 0;
t->read = 0;
/* DEBUG ONLY */
memset(t->data, '*', size);
/* printk("Flip recycle %p\n", t); */
@ -335,6 +339,7 @@ int tty_buffer_request_room(struct tty_struct *tty, size_t size)
if (b != NULL) {
b->next = n;
b->active = 0;
b->commit = b->used;
} else
tty->buf.head = n;
tty->buf.tail = n;
@ -2752,6 +2757,9 @@ static void flush_to_ldisc(void *private_)
unsigned long flags;
struct tty_ldisc *disc;
struct tty_buffer *tbuf;
int count;
char *char_buf;
unsigned char *flag_buf;
disc = tty_ldisc_ref(tty);
if (disc == NULL) /* !TTY_LDISC */
@ -2765,16 +2773,20 @@ static void flush_to_ldisc(void *private_)
goto out;
}
spin_lock_irqsave(&tty->buf.lock, flags);
while((tbuf = tty->buf.head) != NULL && !tbuf->active) {
while((tbuf = tty->buf.head) != NULL) {
while ((count = tbuf->commit - tbuf->read) != 0) {
char_buf = tbuf->char_buf_ptr + tbuf->read;
flag_buf = tbuf->flag_buf_ptr + tbuf->read;
tbuf->read += count;
spin_unlock_irqrestore(&tty->buf.lock, flags);
disc->receive_buf(tty, char_buf, flag_buf, count);
spin_lock_irqsave(&tty->buf.lock, flags);
}
if (tbuf->active)
break;
tty->buf.head = tbuf->next;
if (tty->buf.head == NULL)
tty->buf.tail = NULL;
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->buf.lock, flags);
tty_buffer_free(tty, tbuf);
}
spin_unlock_irqrestore(&tty->buf.lock, flags);
@ -2871,8 +2883,10 @@ void tty_flip_buffer_push(struct tty_struct *tty)
{
unsigned long flags;
spin_lock_irqsave(&tty->buf.lock, flags);
if (tty->buf.tail != NULL)
if (tty->buf.tail != NULL) {
tty->buf.tail->active = 0;
tty->buf.tail->commit = tty->buf.tail->used;
}
spin_unlock_irqrestore(&tty->buf.lock, flags);
if (tty->low_latency)

4
include/linux/kbd_kern.h
View file

@ -153,8 +153,10 @@ static inline void con_schedule_flip(struct tty_struct *t)
{
unsigned long flags;
spin_lock_irqsave(&t->buf.lock, flags);
if (t->buf.tail != NULL)
if (t->buf.tail != NULL) {
t->buf.tail->active = 0;
t->buf.tail->commit = t->buf.tail->used;
}
spin_unlock_irqrestore(&t->buf.lock, flags);
schedule_work(&t->buf.work);
}

2
include/linux/tty.h
View file

@ -58,6 +58,8 @@ struct tty_buffer {
int used;
int size;
int active;
int commit;
int read;
/* Data points here */
unsigned long data[0];
};

4
include/linux/tty_flip.h
View file

@ -29,8 +29,10 @@ _INLINE_ void tty_schedule_flip(struct tty_struct *tty)
{
unsigned long flags;
spin_lock_irqsave(&tty->buf.lock, flags);
if (tty->buf.tail != NULL)
if (tty->buf.tail != NULL) {
tty->buf.tail->active = 0;
tty->buf.tail->commit = tty->buf.tail->used;
}
spin_unlock_irqrestore(&tty->buf.lock, flags);
schedule_delayed_work(&tty->buf.work, 1);
}