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authorHendrik Brueckner <brueckner@linux.vnet.ibm.com>2008-10-13 23:12:50 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2008-10-22 10:59:55 +1100
commit3feebbb5492e9e463467cefb633e23a3dfcec132 (patch)
treeaab5c73bbcd799781b8b27f7173c3e726ea403be
parent56ce9e2b2463b3b257098aa966586701d9967f1e (diff)
hvc_console: Fix loop if put_char() returns 0
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>
-rw-r--r--drivers/char/hvc_console.c20
1 files changed, 11 insertions, 9 deletions
diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index c9d16665c96..3650c904401 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -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)