From: Hendrik Brueckner <[EMAIL PROTECTED]>
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 <[EMAIL PROTECTED]>
Tested-by: Christian Borntraeger <[EMAIL PROTECTED]> (virtio_console)
Signed-off-by: Hendrik Brueckner <[EMAIL PROTECTED]>
---
drivers/char/hvc_console.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -161,7 +161,7 @@ static void hvc_console_print(struct con
}
} 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
* 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 *
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 *
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)
--
Hendrik Brueckner
D/3303 Linux on System z Development
Tel: +49 7031 16-1073
Fax: +49 7031 16-3456
eMail: [EMAIL PROTECTED]
IBM Deutschland Research & Development GmbH, Schoenaicher Str. 220, 71032
Boeblingen
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter
Geschaeftsfuehrung: Erich Baier
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294
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