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Commit ec97eaad authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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tty: hvc: hvc_poll() break hv read loop 



Avoid looping with the spinlock held while there is read data
being returned from the hv driver. Instead note if the entire
size returned by tty_buffer_request_room was read, and request
another read poll.

This limits the critical section lengths, and provides more
even service to other consoles in case there is a pathological
condition.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent a9bf5c8a

drivers/tty/hvc/hvc_console.c

+45 −43
Original line number Diff line number Diff line
@@ -592,7 +592,7 @@ static u32 timeout = MIN_TIMEOUT; 
int hvc_poll(struct hvc_struct *hp)

{

	struct tty_struct *tty;

	int i, n, poll_mask = 0;

	int i, n, count, poll_mask = 0;

	char buf[N_INBUF] __ALIGNED__;

	unsigned long flags;

	int read_total = 0;
@@ -618,7 +618,7 @@ int hvc_poll(struct hvc_struct *hp) 


	/* Now check if we can get data (are we throttled ?) */

	if (tty_throttled(tty))

		goto throttled;

		goto out;



	/* If we aren't notifier driven and aren't throttled, we always

	 * request a reschedule
@@ -627,13 +627,13 @@ int hvc_poll(struct hvc_struct *hp) 
		poll_mask |= HVC_POLL_READ;



	/* Read data if any */

	for (;;) {

		int count = tty_buffer_request_room(&hp->port, N_INBUF);



	count = tty_buffer_request_room(&hp->port, N_INBUF);



	/* If flip is full, just reschedule a later read */

	if (count == 0) {

		poll_mask |= HVC_POLL_READ;

			break;

		goto out;

	}



	n = hp->ops->get_chars(hp->vtermno, buf, count);
@@ -651,8 +651,9 @@ int hvc_poll(struct hvc_struct *hp) 
			 */

			poll_mask |= HVC_POLL_READ;

		}

			break;

		goto out;

	}



	for (i = 0; i < n; ++i) {

#ifdef CONFIG_MAGIC_SYSRQ

		if (hp->index == hvc_console.index) {
@@ -673,10 +674,11 @@ int hvc_poll(struct hvc_struct *hp) 
#endif /* CONFIG_MAGIC_SYSRQ */

		tty_insert_flip_char(&hp->port, buf[i], 0);

	}

	if (n == count)

		poll_mask |= HVC_POLL_READ;

	read_total = n;



		read_total += n;

	}

 throttled:

 out:

	/* Wakeup write queue if necessary */

	if (hp->do_wakeup) {

		hp->do_wakeup = 0;