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hvc_console: Fix loop if put_char() returns 0

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If put_char() routine of a hvc console backend returns 0, then the
hvc console starts looping in the following scenarios:

1. hvc_console_print()
	If put_char() returns 0 then the while loop may loop forever.
	I have added the missing check for 0 to throw away console messages.

2. khvcd may loop:
	The thread calls hvc_poll() --> hvc_push()... if there are still
	buffered data then the HVC_POLL_WRITE bit is set and causes the
	khvcd thread to loop (if yield() returns immediately).

	However, instead of looping, the khvcd thread could sleep for
	MIN_TIMEOUT (doing the same as for get_chars()).
	The MIN_TIMEOUT is set if hvc_push() was not able to write
	data to the backend. If data has been written, the timeout is
	set to 0 to immediately re-schedule hvc_poll().

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> (virtio_console)
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Hendrik Brueckner 2008-10-13 23:12:50 +00:00 committed by Benjamin Herrenschmidt
parent 56ce9e2b24
commit 3feebbb549
1 changed files with 11 additions and 9 deletions
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20
drivers/char/hvc_console.c
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@ -161,7 +161,7 @@ static void hvc_console_print(struct console *co, const char *b,
}
} else {
r = cons_ops[index]->put_chars(vtermnos[index], c, i);
if (r < 0) {
if (r <= 0) {
/* throw away chars on error */
i = 0;
} else if (r > 0) {
@ -431,7 +431,7 @@ static void hvc_hangup(struct tty_struct *tty)
* Push buffered characters whether they were just recently buffered or waiting
* on a blocked hypervisor. Call this function with hp->lock held.
*/
static void hvc_push(struct hvc_struct *hp)
static int hvc_push(struct hvc_struct *hp)
{
int n;
@ -439,7 +439,7 @@ static void hvc_push(struct hvc_struct *hp)
if (n <= 0) {
if (n == 0) {
hp->do_wakeup = 1;
return;
return 0;
}
/* throw away output on error; this happens when
there is no session connected to the vterm. */
@ -450,6 +450,8 @@ static void hvc_push(struct hvc_struct *hp)
memmove(hp->outbuf, hp->outbuf + n, hp->n_outbuf);
else
hp->do_wakeup = 1;
return n;
}
static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count)
@ -538,16 +540,20 @@ int hvc_poll(struct hvc_struct *hp)
char buf[N_INBUF] __ALIGNED__;
unsigned long flags;
int read_total = 0;
int written_total = 0;
spin_lock_irqsave(&hp->lock, flags);
/* Push pending writes */
if (hp->n_outbuf > 0)
hvc_push(hp);
written_total = hvc_push(hp);
/* Reschedule us if still some write pending */
if (hp->n_outbuf > 0)
if (hp->n_outbuf > 0) {
poll_mask |= HVC_POLL_WRITE;
/* If hvc_push() was not able to write, sleep a few msecs */
timeout = (written_total) ? 0 : MIN_TIMEOUT;
}
/* No tty attached, just skip */
tty = hp->tty;
@ -659,10 +665,6 @@ static int khvcd(void *unused)
poll_mask |= HVC_POLL_READ;
if (hvc_kicked)
continue;
if (poll_mask & HVC_POLL_WRITE) {
yield();
continue;
}
set_current_state(TASK_INTERRUPTIBLE);
if (!hvc_kicked) {
if (poll_mask == 0)