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Commit 8977d929 authored by Paul Fulghum's avatar Paul Fulghum Committed by Linus Torvalds
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[PATCH] tty buffering stall fix 



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: default avatarPaul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent f0188f47

drivers/char/tty_io.c

+22 −8
Original line number Diff line number Diff line
@@ -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)

include/linux/kbd_kern.h

+3 −1
Original line number Diff line number Diff line
@@ -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);

}

include/linux/tty.h

+2 −0
Original line number Diff line number Diff line
@@ -58,6 +58,8 @@ struct tty_buffer { 
	int used;

	int size;

	int active;

	int commit;

	int read;

	/* Data points here */

	unsigned long data[0];

};

include/linux/tty_flip.h

+3 −1
Original line number Diff line number Diff line
@@ -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);

}