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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: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2018-05-01 00:55:54 +10:00 committed by Michael Ellerman
parent a9bf5c8a27
commit ec97eaad13
1 changed files with 51 additions and 49 deletions
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100
drivers/tty/hvc/hvc_console.c
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@ -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
@ -627,56 +627,58 @@ 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);
/* If flip is full, just reschedule a later read */
if (count == 0) {
poll_mask |= HVC_POLL_READ;
break;
}
count = tty_buffer_request_room(&hp->port, N_INBUF);
n = hp->ops->get_chars(hp->vtermno, buf, count);
if (n <= 0) {
/* Hangup the tty when disconnected from host */
if (n == -EPIPE) {
spin_unlock_irqrestore(&hp->lock, flags);
tty_hangup(tty);
spin_lock_irqsave(&hp->lock, flags);
} else if ( n == -EAGAIN ) {
/*
* Some back-ends can only ensure a certain min
* num of bytes read, which may be > 'count'.
* Let the tty clear the flip buff to make room.
*/
poll_mask |= HVC_POLL_READ;
}
break;
}
for (i = 0; i < n; ++i) {
#ifdef CONFIG_MAGIC_SYSRQ
if (hp->index == hvc_console.index) {
/* Handle the SysRq Hack */
/* XXX should support a sequence */
if (buf[i] == '\x0f') { /* ^O */
/* if ^O is pressed again, reset
* sysrq_pressed and flip ^O char */
sysrq_pressed = !sysrq_pressed;
if (sysrq_pressed)
continue;
} else if (sysrq_pressed) {
handle_sysrq(buf[i]);
sysrq_pressed = 0;
continue;
}
}
#endif /* CONFIG_MAGIC_SYSRQ */
tty_insert_flip_char(&hp->port, buf[i], 0);
}
read_total += n;
/* If flip is full, just reschedule a later read */
if (count == 0) {
poll_mask |= HVC_POLL_READ;
goto out;
}
throttled:
n = hp->ops->get_chars(hp->vtermno, buf, count);
if (n <= 0) {
/* Hangup the tty when disconnected from host */
if (n == -EPIPE) {
spin_unlock_irqrestore(&hp->lock, flags);
tty_hangup(tty);
spin_lock_irqsave(&hp->lock, flags);
} else if ( n == -EAGAIN ) {
/*
* Some back-ends can only ensure a certain min
* num of bytes read, which may be > 'count'.
* Let the tty clear the flip buff to make room.
*/
poll_mask |= HVC_POLL_READ;
}
goto out;
}
for (i = 0; i < n; ++i) {
#ifdef CONFIG_MAGIC_SYSRQ
if (hp->index == hvc_console.index) {
/* Handle the SysRq Hack */
/* XXX should support a sequence */
if (buf[i] == '\x0f') { /* ^O */
/* if ^O is pressed again, reset
* sysrq_pressed and flip ^O char */
sysrq_pressed = !sysrq_pressed;
if (sysrq_pressed)
continue;
} else if (sysrq_pressed) {
handle_sysrq(buf[i]);
sysrq_pressed = 0;
continue;
}
}
#endif /* CONFIG_MAGIC_SYSRQ */
tty_insert_flip_char(&hp->port, buf[i], 0);
}
if (n == count)
poll_mask |= HVC_POLL_READ;
read_total = n;
out:
/* Wakeup write queue if necessary */
if (hp->do_wakeup) {
hp->do_wakeup = 0;