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tty: hvc: hvc_poll() break hv read loop

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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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20
drivers/tty/hvc/hvc_console.c
View file

@ -592,7 +592,7 @@ static u32 timeout = MIN_TIMEOUT;
int hvc_poll(struct hvc_struct *hp) int hvc_poll(struct hvc_struct *hp)
{ {
struct tty_struct *tty; struct tty_struct *tty;
int i, n, poll_mask = 0; int i, n, count, poll_mask = 0;
char buf[N_INBUF] __ALIGNED__; char buf[N_INBUF] __ALIGNED__;
unsigned long flags; unsigned long flags;
int read_total = 0; 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 ?) */ /* Now check if we can get data (are we throttled ?) */
if (tty_throttled(tty)) if (tty_throttled(tty))
goto throttled; goto out;
/* If we aren't notifier driven and aren't throttled, we always /* If we aren't notifier driven and aren't throttled, we always
* request a reschedule * request a reschedule
@ -627,13 +627,13 @@ int hvc_poll(struct hvc_struct *hp)
poll_mask |= HVC_POLL_READ; poll_mask |= HVC_POLL_READ;
/* Read data if any */ /* 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 flip is full, just reschedule a later read */
if (count == 0) { if (count == 0) {
poll_mask |= HVC_POLL_READ; poll_mask |= HVC_POLL_READ;
break; goto out;
} }
n = hp->ops->get_chars(hp->vtermno, buf, count); 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; poll_mask |= HVC_POLL_READ;
} }
break; goto out;
} }
for (i = 0; i < n; ++i) { for (i = 0; i < n; ++i) {
#ifdef CONFIG_MAGIC_SYSRQ #ifdef CONFIG_MAGIC_SYSRQ
if (hp->index == hvc_console.index) { if (hp->index == hvc_console.index) {
@ -673,10 +674,11 @@ int hvc_poll(struct hvc_struct *hp)
#endif /* CONFIG_MAGIC_SYSRQ */ #endif /* CONFIG_MAGIC_SYSRQ */
tty_insert_flip_char(&hp->port, buf[i], 0); tty_insert_flip_char(&hp->port, buf[i], 0);
} }
if (n == count)
poll_mask |= HVC_POLL_READ;
read_total = n;
read_total += n; out:
}
throttled:
/* Wakeup write queue if necessary */ /* Wakeup write queue if necessary */
if (hp->do_wakeup) { if (hp->do_wakeup) {
hp->do_wakeup = 0; hp->do_wakeup = 0;