On 10/24/2014 10:13 AM, Heinz Graalfs wrote:
> On s390 one can observe system hang situations wrt console input when
> using 'dataplane=on'.
>
> dataplane processing causes an inactive main thread and an active
> dataplane thread.
>
> When a character backend descriptor disappears from the main thread's
> poll() descriptor array (when can_read() returns 0) it happens that it
> will never reappear in the poll() array due to missing poll() interrupts.
>
> The following patches fix observed hangs on s390 and provide a means
> to avoid potential hangs in other backends/frontends.
I think all you need is a simple
qemu_notify_event();
call when can_read can go from 0 to 1, for example just before
get_console_data returns (for hw/char/sclpconsole-lm.c).
By the way, for hw/char/sclpconsole-lm.c I'm not sure what happens if
scon->length == SIZE_CONSOLE_BUFFER. You cannot read, so you cannot
generate an event, and you cannot reset scon->length because you cannot
generate an event. I think something like this is needed:
diff --git a/hw/char/sclpconsole-lm.c b/hw/char/sclpconsole-lm.c
index 80dd0a9..c61b77b 100644
--- a/hw/char/sclpconsole-lm.c
+++ b/hw/char/sclpconsole-lm.c
@@ -61,10 +61,9 @@ static int chr_can_read(void *opaque)
if (scon->event.event_pending) {
return 0;
- } else if (SIZE_CONSOLE_BUFFER - scon->length) {
+ } else {
return 1;
}
- return 0;
}
static void chr_read(void *opaque, const uint8_t *buf, int size)
@@ -78,6 +77,10 @@ static void chr_read(void *opaque, const uint8_t
*buf, int size)
sclp_service_interrupt(0);
return;
}
+ if (scon->length == SIZE_CONSOLE_BUFFER) {
+ /* Eat the character, but still process CR and LF. */
+ return;
+ }
scon->buf[scon->length] = *buf;
scon->length += 1;
if (scon->echo) {
Paolo
